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	$ 531,182	531,182	0	0	0	531,182	0
Net foreign currency translation adjustment, net of tax	(186)	(186)	0	0	0	0	(186)
Net unrealized loss on investments, net of tax		11,817	0	0	0	0	11,817
Repurchases of common stock under incentive plans		(154)	0	(154)	0	0	0
Stock Issued During Period, Value, New Issues		247,188	18	0	247,170	0	0
Stock Issued During Period, Value, Employee Benefit Plan		922	0	0	922	0	0
Issuance of common stock under incentive plans		175	0	0	175	0	0
Stock-based compensation expense, net		5,200	0	0	5,200	0	0
Dividends declared		(1,388)	0	0	(1,388)	0	0
Ending Balance, at Sep. 30, 2014		1,734,401	209	(892,961)	2,599,183	(21,044)	49,014
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	212,396	212,396	0	0	0	212,396	0
Net foreign currency translation adjustment, net of tax	(88)	(88)	0	0	0	0	(88)
Net unrealized loss on investments, net of tax		(58,816)	0	0	0	0	(58,816)
Repurchases of common stock under incentive plans		(215)	0	(215)	0	0	0
Stock Issued During Period, Value, Employee Benefit Plan		1,110	0	0	1,110	0	0
Issuance of common stock under incentive plans		1,285	1	0	1,284	0	0
Stock-based compensation expense, net		13,214	0	0	13,214	0	0
Stock Issued During Period, Value, Conversion of Convertible Securities		349,219	28	0	349,191	0	0
Stock Repurchased During Period, Value		(202,000)	(11)	0	(201,989)	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		11,911	0	0	11,911	0	0
Dividends, Common Stock, Cash		(1,479)	0	0	0	(1,479)	0
Ending Balance, at Sep. 30, 2015	$ 2,435,570	$ 2,435,570	$ 224	$ (893,176)	$ 2,718,210	$ 617,731	$ (7,419)