CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock Convertible Senior Notes 1.25 Percent Due 2020	Common Stock Convertible Senior Notes 0.375 Percent Due 2018	Common Stock	Additional Paid-in Capital Convertible Senior Notes 1.25 Percent Due 2020	Additional Paid-in Capital Convertible Senior Notes 0.375 Percent Due 2018	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Convertible Senior Notes 1.25 Percent Due 2020	Convertible Senior Notes 0.375 Percent Due 2018	Total
Balances at Dec. 31, 2015			$ 187			$ 1,950,764	$ (809)	$ (1,778,987)			$ 171,155
Increase (Decrease) in Stockholders' Equity
Issuance of shares of Common Stock upon exercise of stock options and settlement of employee restricted stock units and shares of Common Stock under the ESPP			2			49,661					49,663
Issuance of shares of Common Stock upon conversion of Convertible Senior Notes				$ 4	$ 5				$ 4	$ 5
Issuance of shares of Common Stock for services rendered						294					294
Stock compensation						96,201					96,201
Other comprehensive loss							(2,077)				(2,077)
Net income (loss)								104,222			104,222
Balances at Dec. 31, 2016			189			2,096,929	(2,886)	(1,674,765)			419,467
Increase (Decrease) in Stockholders' Equity
Issuance of shares of Common Stock upon exercise of stock options and settlement of employee restricted stock units and shares of Common Stock under the ESPP			3			66,732					66,735
Issuance of shares of Common Stock upon conversion of Convertible Senior Notes	$ 7	$ 7		$ 330,004	351,037				$ 330,011	351,044
Issuance of shares of Common Stock for services rendered						294					294
Issuance of shares of Common Stock			5			649,382					649,387
Stock compensation						133,055					133,055
Other comprehensive loss							(4,124)				(4,124)
Adoption of ASU No. 2016-01 (Note 1)								(2,098)			(2,098)
Net income (loss)								(313,142)			(313,142)
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 and shares of Common Stock under the ESPP			2			29,940					29,942
Issuance of shares of Common Stock upon conversion of Convertible Senior Notes					$ 7,695					$ 7,695
Issuance of shares of Common Stock for services rendered						344					344
Stock compensation						148,266					148,266
Other comprehensive loss							(402)				(402)
Adoption of ASU No. 2016-01 (Note 1)							(2,753)	2,753
Net income (loss)								109,493			109,493
Balances at Dec. 31, 2018			$ 213			$ 3,813,678	$ (10,165)	$ (1,877,759)			$ 1,925,967