Consolidated Statements of Stockholders' Equity/Deficit-Unaudited - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Gain (Loss)	Treasury Stock
Balance, shares at Dec. 31, 2020		142,289
Balance, value at Dec. 31, 2020	$ 156,371	$ 142	$ 1,561,096	$ (1,400,018)	$ (6)	$ (4,843)
Stock-based compensation	2,851	0	2,851	0	0	0
Repurchase of common stock	(2,675)	0	0	0	0	(2,675)
Net loss	(20,958)	0	0	(20,958)	0	0
Unrealized gain on investments	11	$ 0	0	0	11	0
Balance, shares at Mar. 31, 2021		145,552
Balance, value at Mar. 31, 2021	152,547	$ 145	1,580,891	(1,420,976)	5	(7,518)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures		1,263
Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture	$ 548	$ 1	547	0	0	0
Balance, shares at Dec. 31, 2021	150,082	150,082
Balance, value at Dec. 31, 2021	$ 113,595	$ 150	1,608,749	(1,487,776)	(10)	(7,518)
Stock-based compensation	2,772	$ 0	2,772	0	0	0
Issuance of common stock under Equity Incentive Plans, shares		0
Issuance of common stock under Equity Incentive Plans, value	(864)	$ 0	0	0	0	(864)
Net loss	(23,476)	0	0	(23,476)	0	0
Unrealized gain on investments	$ (27)	$ 0	0	0	(27)	0
Balance, shares at Mar. 31, 2022	150,082	150,082
Balance, value at Mar. 31, 2022	$ 92,698	$ 150	1,605,898	(1,511,252)	(37)	(2,061)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures		0
Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture	$ 698	$ 0	$ 698	$ 0	$ 0	$ 0