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, 2017	$ 475,475	$ 5	$ (113)	$ 1,066,059	$ (29)	$ (590,447)
Balances, Shares at Dec. 31, 2017		42,002,934	960
Issuance of common stock from exercise of stock options, Amount	27,014			27,014
Issuance of common stock from exercise of stock options, Shares		824,188
Issuance of common stock under the employee stock purchase plan	2,705			2,705
Issuance of common stock under the employee stock purchase plan, Shares		19,687
Purchase of treasury stock, Amount	(98)		$ (98)
Purchase of treasury stock, Shares			2,073
Stock-based compensation expense	100,993			100,993
Public offering of common stock, net of offering costs, Amount	631,154			631,154
Public offering of common stock, net of offering costs, Shares		4,032,012
Unrealized gain (loss) on available-for-sale securities	(486)				(486)
Vesting of restricted stock units, net of employee tax obligations	(904)			(904)
Vesting of restricted stock units, net of employee tax obligations, Shares		9,442
Net income (loss)	(372,882)					(372,882)
Balances at Dec. 31, 2018	862,971	$ 5	$ (211)	1,827,021	(515)	(963,329)
Balances, Shares at Dec. 31, 2018		46,888,263	3,033
Issuance of common stock from exercise of stock options, Amount	44,276			44,276
Issuance of common stock from exercise of stock options, Shares		1,031,989
Issuance of common stock under the employee stock purchase plan	5,744			5,744
Issuance of common stock under the employee stock purchase plan, Shares		55,404
Purchase of treasury stock, Amount	(189)		$ (189)
Stock-based compensation expense	151,508			151,508
Public offering of common stock, net of offering costs, Amount	560,948			560,948
Public offering of common stock, net of offering costs, Shares		3,833,334
Unrealized gain (loss) on available-for-sale securities	1,810				1,810
Vesting of restricted stock units, net of employee tax obligations	(2,175)			(2,175)
Vesting of restricted stock units, net of employee tax obligations, Shares		68,204
Net income (loss)	(680,238)					(680,238)
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 exercise of stock options, Amount	5,082			5,082
Issuance of common stock from exercise of stock options, Shares		117,025
Issuance of common stock under the employee stock purchase plan	4,936			4,936
Issuance of common stock under the employee stock purchase plan, Shares		72,719
Issuance of common stock under the Stock Purchase Agreement	$ 417,500	$ 1		417,499
Issuance of common stock under the Stock Purchase Agreement, Shares		6,241,473
Purchase of treasury stock, Shares	(3,033)
Stock-based compensation expense	$ 94,968			94,968
Unrealized gain (loss) on available-for-sale securities	(880)				(880)
Net income (loss)	606,073					606,073
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