CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Common Stock [Member] 4.75% Convertible Senior Notes Due 2015	Common Stock [Member] Convertible Senior Notes 1.25 Percent Due 2020	Common Stock [Member] Convertible Senior Notes 0.375 Percent Due 2018	Common Stock [Member]	Additional Paid-in Capital [Member] 4.75% Convertible Senior Notes Due 2015	Additional Paid-in Capital [Member] Convertible Senior Notes 1.25 Percent Due 2020	Additional Paid-in Capital [Member] Convertible Senior Notes 0.375 Percent Due 2018	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	4.75% Convertible Senior Notes Due 2015	Convertible Senior Notes 1.25 Percent Due 2020	Convertible Senior Notes 0.375 Percent Due 2018	Total
Balances at Dec. 31, 2014				$ 171				$ 1,701,904	$ 1,815	$ (1,785,518)				$ (81,628)
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				5				86,755						86,760
Issuance of shares of Common Stock upon conversion of Convertible Senior Notes	$ 11				$ 88,963	$ 180					$ 88,974	$ 180
Issuance of shares of Common Stock for services rendered								218						218
Excess tax provision from stock based compensation								2,872						2,872
Stock compensation expense								69,872						69,872
Other comprehensive loss									(2,624)					(2,624)
Net income (loss)										6,531				6,531
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 expense								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 expense								133,055						133,055
Other comprehensive loss									(4,124)					(4,124)
Adoption of accounting standard (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