CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Total
Increase (Decrease) in Stockholders' Equity
Adoption of ASU | ASU 2016-01			$ (2,753)	$ 2,753
Balances at Dec. 31, 2017	$ 211	$ 3,627,433	(7,010)	(1,990,005)	$ 1,630,629
Increase (Decrease) in Stockholders' Equity
Issuance of shares of Common Stock upon exercise of stock options and settlement of employee restricted stock units	1	2,575			2,576
Issuance of shares of Common Stock for services rendered		87			87
Issuance of shares of Common Stock upon conversion of Convertible Senior Notes		27			27
Stock compensation		36,224			36,224
Other comprehensive income (loss)			(359)		(359)
Net income				(41,140)	(41,140)
Balances at Mar. 31, 2018	212	3,666,346	(10,122)	(2,028,392)	1,628,044
Balances at Dec. 31, 2017	211	3,627,433	(7,010)	(1,990,005)	1,630,629
Increase (Decrease) in Stockholders' Equity
Other comprehensive income (loss)					(46)
Net income					11,254
Balances at Jun. 30, 2018	212	3,718,518	(9,809)	(1,975,998)	1,732,923
Balances at Mar. 31, 2018	212	3,666,346	(10,122)	(2,028,392)	1,628,044
Increase (Decrease) in Stockholders' Equity
Issuance of shares of Common Stock upon exercise of stock options and settlement of employee restricted stock units		15,480			15,480
Issuance of shares of Common Stock for services rendered		85			85
Issuance of shares of Common Stock upon conversion of Convertible Senior Notes		2			2
Stock compensation		36,605			36,605
Other comprehensive income (loss)			313		313
Net income				52,394	52,394
Balances at Jun. 30, 2018	212	3,718,518	(9,809)	(1,975,998)	1,732,923
Increase (Decrease) in Stockholders' Equity
Adoption of ASU | ASU No. 2016-02				95	95
Balances at Dec. 31, 2018	213	3,813,678	(10,165)	(1,877,759)	1,925,967
Increase (Decrease) in Stockholders' Equity
Issuance of shares of Common Stock upon exercise of stock options and settlement of employee restricted stock units	1	15,480			15,481
Issuance of shares of Common Stock for services rendered		104			104
Stock compensation		40,690			40,690
Other comprehensive income (loss)			918		918
Net income				102,312	102,312
Balances at Mar. 31, 2019	214	3,869,952	(9,247)	(1,775,352)	2,085,567
Balances at Dec. 31, 2018	213	3,813,678	(10,165)	(1,877,759)	1,925,967
Increase (Decrease) in Stockholders' Equity
Other comprehensive income (loss)					1,200
Net income					207,630
Balances at Jun. 30, 2019	215	3,925,975	(8,965)	(1,670,034)	2,247,191
Balances at Mar. 31, 2019	214	3,869,952	(9,247)	(1,775,352)	2,085,567
Increase (Decrease) in Stockholders' Equity
Issuance of shares of Common Stock upon exercise of stock options and settlement of employee restricted stock units	1	15,190			15,191
Issuance of shares of Common Stock for services rendered		123			123
Stock compensation		40,710			40,710
Other comprehensive income (loss)			282		282
Net income				105,318	105,318
Balances at Jun. 30, 2019	$ 215	$ 3,925,975	$ (8,965)	$ (1,670,034)	$ 2,247,191