Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive 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, 2019	944,655	$ 5	$ (400)	2,587,322	1,295	(1,643,567)
Balances, Shares at Dec. 31, 2019		51,877,194	3,033
Net loss	(263,087)
Balances at Jun. 30, 2020	739,915	$ 5	$ (400)	2,645,255	1,709	(1,906,654)
Balance, Shares at Jun. 30, 2020		51,934,979	3,033
Balances at Mar. 31, 2020	849,206	$ 5	$ (400)	2,620,700	(792)	(1,770,307)
Balances, Shares at Mar. 31, 2020		51,917,819	3,033
Issuance of common stock from exercises of stock options, Amount	387			387
Issuance of common stock from exercises of stock options, Shares		17,160
Stock-based compensation expense	24,168			24,168
Unrealized gain (loss) on available-for-sale securities	2,501				2,501
Net loss	(136,347)					(136,347)
Balances at Jun. 30, 2020	739,915	$ 5	$ (400)	2,645,255	1,709	(1,906,654)
Balance, Shares at Jun. 30, 2020		51,934,979	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
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
Net loss	(203,009)
Balances at Jun. 30, 2021	1,929,512	$ 6	$ (400)	3,170,694	(285)	(1,240,503)
Balance, Shares at Jun. 30, 2021		58,770,364	3,033
Balances at Mar. 31, 2021	2,003,276	$ 6	$ (400)	3,137,164	(236)	(1,133,258)
Balances, Shares at Mar. 31, 2021		58,406,821	3,033
Issuance of common stock from exercises of stock options, Amount	6,861			6,861
Issuance of common stock from exercises of stock options, Shares		159,070
Stock-based compensation expense	27,465			27,465
Unrealized gain (loss) on available-for-sale securities	(49)				(49)
Vesting of restricted stock units, net of employee tax obligations	(796)			(796)
Vesting of restricted stock units, net of employee tax obligations, Shares		204,473
Net loss	(107,245)					(107,245)
Balances at Jun. 30, 2021	$ 1,929,512	$ 6	$ (400)	$ 3,170,694	$ (285)	$ (1,240,503)
Balance, Shares at Jun. 30, 2021		58,770,364	3,033