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, 2014			$ 209	$ (892,961)	$ 2,531,513	$ 406,814	$ 51,485
Impact of extinguishment of Convertible Senior Notes due 2017 and 2019 (Note 12)			28
Issuance of common stock under incentive and benefit plans			1		2,422
Stock-based compensation					15,513
Termination of capped calls (Note 12)			(3)		13,153
Impact of extinguishment of Convertible Senior Notes due 2017 and 2019 (Note 12)					336,358
Shares repurchased under share repurchase program (Note 14)			(11)		(201,989)
Repurchases of common stock under incentive plans				(215)
Change in equity component of currently redeemable convertible senior notes					19,648
Net income	$ 286,924					286,924
Dividends declared						(1,996)
Net foreign currency translation adjustment, net of tax	(217)						(217)
Net unrealized gains (losses) on investments, net of tax							(66,756)
Activity related to investments recorded as assets held for sale							(3,254)
Net actuarial gains	265						265
Balance, at Dec. 31, 2015		$ 2,496,931	224	(893,176)	2,716,618	691,742	(18,477)
Impact of extinguishment of Convertible Senior Notes due 2017 and 2019 (Note 12)			17
Issuance of common stock under incentive and benefit plans			0		2,117
Stock-based compensation					18,257
Termination of capped calls (Note 12)			0		0
Impact of extinguishment of Convertible Senior Notes due 2017 and 2019 (Note 12)					143,078
Shares repurchased under share repurchase program (Note 14)			(9)		(100,179)
Repurchases of common stock under incentive plans				(156)
Change in equity component of currently redeemable convertible senior notes					0
Net income	308,253					308,253
Dividends declared						(2,105)
Net foreign currency translation adjustment, net of tax	(474)						(474)
Net unrealized gains (losses) on investments, net of tax							6,531
Activity related to investments recorded as assets held for sale							0
Net actuarial gains	25						25
Balance, at Dec. 31, 2016	2,872,286	2,872,286	232	(893,332)	2,779,891	997,890	(12,395)
Impact of extinguishment of Convertible Senior Notes due 2017 and 2019 (Note 12)			0
Issuance of common stock under incentive and benefit plans			1		8,635
Stock-based compensation					13,491
Termination of capped calls (Note 12)			0		4,208
Impact of extinguishment of Convertible Senior Notes due 2017 and 2019 (Note 12)					(52,700)
Shares repurchased under share repurchase program (Note 14)			0		(6)
Repurchases of common stock under incentive plans				(556)
Change in equity component of currently redeemable convertible senior notes					0
Net income	121,088					121,088
Dividends declared						(2,154)
Net foreign currency translation adjustment, net of tax	871						871
Net unrealized gains (losses) on investments, net of tax							34,545
Activity related to investments recorded as assets held for sale							0
Net actuarial gains	64						64
Balance, at Dec. 31, 2017	$ 3,000,038	$ 3,000,038	$ 233	$ (893,888)	2,754,275	1,116,333	$ 23,085
Cumulative effect of adoption of the accounting standard update for share-based payment transactions					$ 756	$ (491)