Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Balances at Dec. 31, 2019	$ 944,655	$ 5	$ (400)	$ 2,587,322	$ 1,295	$ (1,643,567)
Balances, Shares at Dec. 31, 2019		51,877,194	3,033
Issuance of common stock from exercises of stock options, Amount	367			367
Issuance of common stock from exercises of stock options, Shares		7,196
Issuance of common stock under the employee stock purchase plan	2,793			2,793
Issuance of common stock under the employee stock purchase plan, Shares		33,429
Stock-based compensation expense	30,218			30,218
Unrealized gain (loss) on available-for-sale securities	(2,087)				(2,087)
Net loss	(126,740)					(126,740)
Balances at Mar. 31, 2020	849,206	$ 5	$ (400)	2,620,700	(792)	(1,770,307)
Balance, Shares at Mar. 31, 2020		51,917,819	3,033
Balances at Dec. 31, 2020	2,072,334	$ 6	$ (400)	3,109,807	415	(1,037,494)
Balances, Shares at Dec. 31, 2020		58,308,411	3,033
Issuance of common stock from exercises of stock options, Amount	4,687			4,687
Issuance of common stock from exercises of stock options, Shares		80,338
Issuance of common stock under the employee stock purchase plan	936			936
Issuance of common stock under the employee stock purchase plan, Shares		18,072
Stock-based compensation expense	21,734			21,734
Unrealized gain (loss) on available-for-sale securities	(651)				(651)
Net loss	(95,764)					(95,764)
Balances at Mar. 31, 2021	$ 2,003,276	$ 6	$ (400)	$ 3,137,164	$ (236)	$ (1,133,258)
Balance, Shares at Mar. 31, 2021		58,406,821	3,033