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, 2018		106,162
Balance, value at Dec. 31, 2018	$ (26,405)	$ 106	$ 1,447,954	$ (1,471,577)	$ (12)	$ (2,876)
Stock-based compensation	3,411	$ 0	3,411	0	0	0
Issuance of common stock under Equity Incentive Plans, shares		517
Issuance of common stock under Equity Incentive Plans, value	0	$ 0	0	0	0	0
Repurchase of common stock	(941)	0	0	0	0	(941)
Net loss	(21,797)	0	0	(21,797)	0	0
Unrealized gain on investments	$ 45	$ 0	0	0	45	0
Balance, shares at Mar. 31, 2019	106,679	106,679
Balance, value at Mar. 31, 2019	$ (45,687)	$ 106	1,451,365	(1,493,374)	33	(3,817)
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
Issuance of common stock under Equity Incentive Plans, shares		1,032
Issuance of common stock under Equity Incentive Plans, value	2	$ 2	0	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	107,711
Balance, value at Mar. 31, 2020	$ 54,777	$ 108	$ 1,466,604	$ (1,408,055)	$ 860	$ (4,740)