Consolidated Statements of Shareholders' Equity (unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Stock Options and ESPP Shares	Common Stock	Common Stock Stock Options and ESPP Shares	Additional Paid-in Capital	Additional Paid-in Capital Stock Options and ESPP Shares	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balance (in shares) at Dec. 31, 2019			89,682
Balance at Dec. 31, 2019	$ 261,674		$ 897		$ 1,797,286		$ (1,536,499)	$ (10)
Comprehensive loss:
Net loss	(66,364)						(66,364)
Other comprehensive loss	(37)							(37)
Exercise of stock options and ESPP shares (in shares)				151
Exercise of stock options and ESPP shares issuance		$ 2,426		$ 2		$ 2,424
Issuance of common stock for vesting of RSUs (in shares)			27
Issuance of common stock for vesting of RSUs	0		$ 0
Stock compensation expense	9,002				9,002
Balance (in shares) at Mar. 31, 2020			89,860
Balance at Mar. 31, 2020	206,701		$ 899		1,808,712		(1,602,863)	(47)
Balance (in shares) at Dec. 31, 2020			102,763
Balance at Dec. 31, 2020	275,884		$ 1,028		2,105,252		(1,830,589)	193
Comprehensive loss:
Net loss	(91,641)						(91,641)
Other comprehensive loss	(103)							(103)
Exercise of stock options and ESPP shares (in shares)				416
Exercise of stock options and ESPP shares issuance		$ 6,960		$ 4		$ 6,956
Issuance of common stock for vesting of RSUs (in shares)			100
Issuance of common stock for vesting of RSUs	1		$ 1
Stock compensation expense	10,535				10,535
Balance (in shares) at Mar. 31, 2021			103,279
Balance at Mar. 31, 2021	$ 201,636		$ 1,033		$ 2,122,743		$ (1,922,230)	$ 90