Condensed Consolidated Statements of Changes in Common Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Parent	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings (Deficit)	Accumulated Other Comprehensive Income
Beginning Balance, at Dec. 31, 2013		$ 939,645	$ 191	$ (892,807)	$ 2,347,104	$ (552,226)	$ 37,383
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 377,592	377,592	0	0	0	377,592	0
Net foreign currency translation adjustment, net of tax	0
Net unrealized loss on investments, net of tax		13,634	0	0	0	0	13,634
Repurchases of common stock under incentive plans		(154)	0	(154)	0	0	0
Stock Issued During Period, Value, New Issues		247,388	18		247,370
Issuance of common stock under benefit plans		487	0	0	487	0	0
Issuance of common stock under incentive plans		175	0	0	175	0	0
Stock-based compensation expense, net		6,390	0	0	6,390	0	0
Dividends declared		(910)	0	0	(910)	0	0
Ending Balance, at Jun. 30, 2014		1,584,247	209	(892,961)	2,600,616	(174,634)	51,017
Beginning Balance, at Dec. 31, 2014	2,097,060	2,097,060	209	(892,961)	2,531,513	406,814	51,485
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	142,305	142,305	0	0	0	142,305	0
Net foreign currency translation adjustment, net of tax	32	32	0	0	0	0	32
Net unrealized loss on investments, net of tax		(63,051)	0	0	0	0	(63,051)
Repurchases of common stock under incentive plans		(215)	0	(215)	0	0	0
Issuance of common stock under benefit plans		482	0	0	482	0	0
Issuance of common stock under incentive plans		1,113	1	0	1,112	0	0
Stock-based compensation expense, net		6,494	0	0	6,494	0	0
Stock Issued During Period, Value, Conversion of Convertible Securities		349,061	28	0	349,033	0	0
Stock Repurchased During Period, Value		(202,000)	(9)	0	(201,991)	0	0
Impact of Termination of Capped Call Transaction		11,973	(3)	0	11,976	0	0
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments		11,102	0	0	11,102	0	0
Dividends, Common Stock, Cash		(958)	0	0	0	(958)	0
Ending Balance, at Jun. 30, 2015	$ 2,353,398	$ 2,353,398	$ 226	$ (893,176)	$ 2,709,721	$ 548,161	$ (11,534)