Consolidated Statements of Changes in Common Stockholders' Equity - USD ($) $ in Thousands	Total	Parent [Member]	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings/(Deficit)	Accumulated Other Comprehensive Income (Loss) [Member]
Balance, at Dec. 31, 2012		$ 736,325	$ 151	$ (892,094)	$ 1,967,414	$ (355,241)	$ 16,095
Net income (loss)	$ (196,985)	(196,985)				(196,985)	0
Net foreign currency translation adjustment, net of tax	0
Net unrealized gain on investments, net of tax	18,493	21,090					21,090
Repurchases of common stock under incentive plans		(713)		(713)	0
Issuance of common stock - stock offering		299,410	39		299,371
Issuance of common stock under incentive plans		63	1		62
Issuance of common stock under benefit plans		672	0		672
Stock-based compensation expense, net		4,191			4,191
Issuance of convertible debt (See Note 11)		77,026			77,026
Net actuarial gain (loss)		198					198
Dividends declared		(1,632)			(1,632)
Dividends, Common Stock						0
Balance, at Dec. 31, 2013		939,645	191	(892,807)	2,347,104	(552,226)	37,383
Net income (loss)	959,517	959,517				959,517
Net foreign currency translation adjustment, net of tax	(226)	(226)					(226)
Net unrealized gain on investments, net of tax	14,689	14,387					14,387
Repurchases of common stock under incentive plans		(154)		(154)	0
Issuance of common stock - stock offering		247,188	18		247,170
Issuance of common stock under incentive plans		182	0		182
Issuance of common stock under benefit plans	0	959	0		959
Stock-based compensation expense, net		12,176			12,176
Net actuarial gain (loss)		(59)					(59)
Adjustments to Additional Paid in Capital, Convertible Debt with Conversion Feature		(74,690)			(74,690)
Dividends declared		(1,865)			(1,388)
Dividends, Common Stock, Cash						477
Balance, at Dec. 31, 2014	2,097,060	2,097,060	209	(892,961)	2,531,513	406,814	51,485
Net income (loss)	286,924	286,924				286,924
Net foreign currency translation adjustment, net of tax	(217)	(217)					(217)
Net unrealized gain on investments, net of tax	(66,756)	(70,010)					(70,010)
Repurchases of common stock under incentive plans		(215)		(215)	0
Issuance of common stock under incentive plans		1,285	1		1,284
Issuance of common stock under benefit plans		1,138	0		1,138
Stock-based compensation expense, net		15,513			15,513
Stock Issued During Period, Value, Conversion of Convertible Securities			28
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments		336,386			336,358
Net actuarial gain (loss)		265	0	0	0	0	265
Stock Repurchased During Period, Value		(202,000)	(11)	0	(201,989)	0	0
Equity Impact of Termination of Capped Call Transaction		13,150	(3)	0	13,153	0	0
Change in equity component of currently redeemable convertible senior notes		19,648			19,648
Dividends declared		(1,996)			0
Dividends, Common Stock, Cash						1,996
Balance, at Dec. 31, 2015	$ 2,496,931	$ 2,496,931	$ 224	$ (893,176)	$ 2,716,618	$ 691,742	$ (18,477)