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, 2019		106,679
Balance, value at Dec. 31, 2019	$ 117,101	$ 106	$ 1,462,172	$ (1,341,444)	$ 84	$ (3,817)
Stock-based compensation	4,432	0	4,432	0	0	0
Repurchase of common stock	(923)	0	0	0	0	(923)
Net loss	(66,611)	0	0	(66,611)	0	0
Unrealized gain on investments	776	$ 0	0	0	776	0
Balance, shares at Mar. 31, 2020		107,711
Balance, value at Mar. 31, 2020	54,777	$ 108	1,466,604	(1,408,055)	860	(4,740)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures		1,032
Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture	$ 2	$ 2	0	0	0	0
Balance, shares at Dec. 31, 2020	142,289	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
Issuance of common stock under Equity Incentive Plans, shares		2,000
Issuance of common stock under Equity Incentive Plans, value	16,399	$ 2	16,397	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	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