Consolidated Statements of Stockholders' (Deficit) Equity - USD ($) shares in Thousands, $ in Thousands |
Preferred Stock |
Common Stock
Registered Direct Offering [Member]
|
Common Stock
Public Warrant Tender Offering [Member]
|
Common Stock
Private Warrant Exchange [Member]
|
Common Stock
Private Equity Offering
|
Common Stock |
Treasury Stock
Public Warrant Tender Offering [Member]
|
Treasury Stock |
Additional Paid-in Capital
Registered Direct Offering [Member]
|
Additional Paid-in Capital
Public Warrant Tender Offering [Member]
|
Additional Paid-in Capital
Private Warrant Exchange [Member]
|
Additional Paid-in Capital
Private Equity Offering
|
Additional Paid-in Capital |
Accumulated Deficit |
Registered Direct Offering [Member] |
Public Warrant Tender Offering [Member] |
Private Warrant Exchange [Member] |
Private Equity Offering |
Total |
Beginning balance at May. 31, 2019 |
|
|
|
|
|
$ 330
|
|
|
|
|
|
|
$ 225,177
|
$ (234,420)
|
|
|
|
|
$ (8,913)
|
Beginning balance, shares at May. 31, 2019 |
95
|
|
|
|
|
329,555
|
|
159
|
|
|
|
|
|
|
|
|
|
|
|
Issuance of stock for convertible note repayment, value |
|
|
|
|
|
$ 23
|
|
|
|
|
|
|
10,799
|
|
|
|
|
|
10,822
|
Issuance of stock for convertible note repayment, shares |
|
|
|
|
|
22,967
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Note conversion and extension fees, value |
|
|
|
|
|
$ 8
|
|
|
|
|
|
|
3,891
|
|
|
|
|
|
3,899
|
Note conversion and extension fees, shares |
|
|
|
|
|
8,232
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Stock issued via offering, tender or placement, value |
|
$ 39
|
$ 45
|
$ 20
|
|
|
|
|
$ 12,627
|
$ 11,855
|
$ 6,001
|
|
13,409
|
|
$ 12,666
|
$ 11,900
|
$ 6,021
|
|
13,409
|
Stock issued via offering, tender or placement, shares |
14
|
38,856
|
45,376
|
20,529
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Warrant exercises, value |
|
|
|
|
|
$ 42
|
|
|
|
|
|
|
20,458
|
|
|
|
|
|
20,500
|
Warrant exercises, shares |
|
|
|
|
|
42,024
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Relative fair market value associated with warrants exercised |
|
|
|
|
|
|
|
|
|
|
|
|
11,949
|
|
|
|
|
|
11,949
|
Inducement interest expense |
|
|
|
|
|
|
|
|
|
2,713
|
|
|
|
|
|
2,713
|
|
|
|
Inducement interest expense related to private warrant exchange, value |
|
|
|
|
|
|
|
|
|
|
|
|
20,724
|
|
|
|
|
|
20,724
|
Dividends accrued and paid on preferred stock, value |
|
|
|
|
|
|
|
|
|
|
|
|
|
(945)
|
|
|
|
|
(945)
|
Legal fees in connection with equity offerings |
|
|
|
|
|
|
|
|
|
|
|
|
(16)
|
|
|
|
|
|
(16)
|
Stock issued for services, value |
|
|
|
|
|
$ 3
|
|
|
|
|
|
|
(3)
|
|
|
|
|
|
|
Stock issued for services, shares |
|
|
|
|
|
2,620
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Stock issued for bonuses and tendered for income tax, value |
|
|
|
|
|
|
|
|
|
|
|
|
154
|
|
|
|
|
|
154
|
Stock issued for bonuses and tendered for income tax, shares |
|
|
|
|
|
380
|
|
127
|
|
|
|
|
|
|
|
|
|
|
|
Stock option exercises, value |
|
|
|
|
|
$ 9
|
|
|
|
|
|
|
5,594
|
|
|
|
|
|
5,603
|
Stock option exercises, shares |
|
|
|
|
|
8,723
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Stock-based compensation |
|
|
|
|
|
|
|
|
|
|
|
|
6,548
|
|
|
|
|
|
6,548
|
Issuance of legal settlement, warrants, value |
|
|
|
|
|
|
|
|
|
|
|
|
22,500
|
|
|
|
|
|
22,500
|
Offering costs, stock and warrants |
|
|
|
|
|
|
|
|
$ (378)
|
(1,059)
|
(197)
|
|
(437)
|
|
$ (378)
|
(1,059)
|
$ (197)
|
|
(437)
|
Exercise of option to repurchase common stock, value |
|
|
|
|
|
|
|
|
|
|
|
|
(8)
|
|
|
|
|
|
(8)
|
Net loss |
|
|
|
|
|
|
|
|
|
|
|
|
|
(139,936)
|
|
|
|
|
(139,936)
|
Ending balance at May. 31, 2020 |
|
|
|
|
|
$ 519
|
|
|
|
|
|
|
372,301
|
(375,301)
|
|
|
|
|
(2,481)
|
Ending balance, shares at May. 31, 2020 |
109
|
|
|
|
|
519,262
|
|
286
|
|
|
|
|
|
|
|
|
|
|
|
Issuance of stock for convertible note repayment, value |
|
|
|
|
|
$ 24
|
|
|
|
|
|
|
96,914
|
|
|
|
|
|
96,938
|
Issuance of stock for convertible note repayment, shares |
|
|
|
|
|
24,154
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Stock issued via offering, tender or placement, value |
|
|
|
|
$ 1
|
|
|
|
|
$ 828
|
|
$ 999
|
|
|
|
$ 828
|
|
$ 1,000
|
|
Stock issued via offering, tender or placement, shares |
|
|
323
|
|
667
|
|
157
|
|
|
|
|
|
|
|
|
|
35,800
|
8,900
|
|
Warrant exercises, value |
|
|
|
$ 37
|
|
$ 38
|
|
|
|
|
17,519
|
|
18,611
|
|
|
|
$ 17,556
|
|
$ 18,649
|
Warrant exercises, shares |
|
|
|
37,054
|
|
37,941
|
|
|
|
|
|
|
|
|
|
|
|
|
26,700
|
Inducement interest expense related to private warrant exchange, value |
|
|
|
|
|
|
|
|
|
|
|
|
13,922
|
|
|
|
|
|
$ 13,922
|
Dividends accrued and paid on preferred stock, value |
|
|
|
|
|
|
|
|
|
|
|
|
|
(1,909)
|
|
|
|
|
(1,909)
|
Stock option exercises, value |
|
|
|
|
|
$ 3
|
|
|
|
|
|
|
1,835
|
|
|
|
|
|
1,838
|
Stock option exercises, shares |
|
|
|
|
|
2,591
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Stock-based compensation |
|
|
|
|
|
|
|
|
|
|
|
|
9,601
|
|
|
|
|
|
$ 9,601
|
Issuance of legal settlement, warrants, value |
|
|
|
|
|
$ 4
|
|
|
|
|
|
|
(4)
|
|
|
|
|
|
|
Issuance of legal settlement, warrants, shares |
|
|
|
|
|
4,000
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Conversion of preferred stock to common stock, shares |
(13)
|
|
|
|
|
131
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Offering costs, stock and warrants |
|
|
|
|
|
|
|
|
|
|
(495)
|
|
|
|
|
|
(495)
|
|
|
Issuance of common stock upon vesting of stock based compensation awards, shares |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
200
|
Net loss |
|
|
|
|
|
|
|
|
|
|
|
|
|
(176,465)
|
|
|
|
|
$ (176,465)
|
Ending balance at May. 31, 2021 |
|
|
|
|
|
$ 626
|
|
|
|
|
|
|
532,031
|
(553,675)
|
|
|
|
|
(21,018)
|
Ending balance, shares at May. 31, 2021 |
96
|
|
|
|
|
626,123
|
|
443
|
|
|
|
|
|
|
|
|
|
|
|
Issuance of stock for convertible note repayment, value |
|
|
|
|
|
$ 37
|
|
|
|
|
|
|
68,344
|
|
|
|
|
|
$ 68,381
|
Issuance of stock for convertible note repayment, shares |
|
|
|
|
|
37,110
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Stock issued via offering, tender or placement, value |
|
|
|
|
$ 38
|
|
|
|
|
|
|
$ 46,473
|
|
|
|
|
|
$ 46,511
|
|
Stock issued via offering, tender or placement, shares |
|
|
|
|
38,035
|
|
|
|
|
|
|
|
|
|
|
|
|
|
7,900
|
Warrant exercises, value |
|
|
|
$ 8
|
|
$ 2
|
|
|
|
|
$ 5,382
|
|
1,034
|
|
|
|
$ 5,390
|
|
$ 1,036
|
Warrant exercises, shares |
|
|
|
7,920
|
|
1,642
|
|
|
|
|
|
|
|
|
|
|
|
|
1,400
|
Inducement interest expense related to private warrant exchange, value |
|
|
|
|
|
$ 2
|
|
|
|
|
|
|
6,689
|
|
|
|
|
|
$ 6,691
|
Inducement interest expense related to private warrant exchange, shares |
|
|
|
|
|
2,293
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Dividends accrued and paid on preferred stock, value |
|
|
|
|
|
$ 1
|
|
|
|
|
|
|
305
|
(1,636)
|
|
|
|
|
(1,330)
|
Dividends accrued and paid on preferred stock, shares |
|
|
|
|
|
613
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Stock issued for bonuses and tendered for income tax, value |
|
|
|
|
|
$ 2
|
|
|
|
|
|
|
666
|
|
|
|
|
|
668
|
Stock issued for bonuses and tendered for income tax, shares |
|
|
|
|
|
2,582
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Stock option exercises, value |
|
|
|
|
|
$ 1
|
|
|
|
|
|
|
389
|
|
|
|
|
|
$ 390
|
Stock option exercises, shares |
|
|
|
|
|
510
|
|
|
|
|
|
|
|
|
|
|
|
|
500
|
Stock-based compensation |
|
|
|
|
|
|
|
|
|
|
|
|
5,571
|
|
|
|
|
|
$ 5,571
|
Issuance of legal settlement, warrants, value |
|
|
|
|
|
|
|
|
|
|
|
|
2,863
|
|
|
|
|
|
2,863
|
Conversion of preferred stock to common stock |
|
|
|
|
|
$ 3
|
|
|
|
|
|
|
(3)
|
|
|
|
|
|
|
Conversion of preferred stock to common stock, shares |
(61)
|
|
|
|
|
3,200
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Finance charges related to warrant issuance for surety bond backstop agreement |
|
|
|
|
|
|
|
|
|
|
|
|
6,585
|
|
|
|
|
|
6,585
|
Offering costs, stock and warrants |
|
|
|
|
|
|
|
|
|
|
|
|
(5,316)
|
|
|
|
|
|
(5,316)
|
Net loss |
|
|
|
|
|
|
|
|
|
|
|
|
|
(210,820)
|
|
|
|
|
(210,820)
|
Ending balance at May. 31, 2022 |
|
|
|
|
|
$ 720
|
|
|
|
|
|
|
$ 671,013
|
$ (766,131)
|
|
|
|
|
$ (94,398)
|
Ending balance, shares at May. 31, 2022 |
35
|
|
|
|
|
720,028
|
|
443
|
|
|
|
|
|
|
|
|
|
|
|