Condensed Consolidated Statements of Changes in Common Stockholders' Equity (Unaudited) (USD $) In Thousands, unless otherwise specified	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	202,759	202,759	0	0	0	202,759	0
Net foreign currency translation adjustment, net of tax	0
Net unrealized gain on investments, net of tax		3,961	0	0	0	0	3,961
Repurchases of common stock under incentive plans		(130)	0	(130)	0	0	0
Issuance of common stock under benefit plans		458	0	0	458	0	0
Issuance of common stock under incentive plans		13	0	0	13	0	0
Stock-based compensation expense, net		310	0	0	310	0	0
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments		(91,016)	0	0	(91,016)	0	0
Dividends declared		(433)	0	0	(433)	0	0
Ending Balance, at Mar. 31, 2014		1,055,567	191	(892,937)	2,256,436	(349,467)	41,344
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	92,257	92,257	0	0	0	92,257	0
Net foreign currency translation adjustment, net of tax	(126)	(126)	0	0	0	0	(126)
Net unrealized gain on investments, net of tax		8,315	0	0	0	0	8,315
Repurchases of common stock under incentive plans		(188)	0	(188)	0	0	0
Issuance of common stock under benefit plans		452	0	0	452	0	0
Issuance of common stock under incentive plans		789	0	0	789	0	0
Stock-based compensation expense, net		3,123	0	0	3,123	0	0
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments		5,708	0	0	5,708	0	0
Dividends declared			0	0	0
Dividends, Common Stock, Cash		(478)				(478)	0
Ending Balance, at Mar. 31, 2015	$ 2,206,912	$ 2,206,912	$ 209	$ (893,149)	$ 2,541,585	$ 498,593	$ 59,674