Condensed Consolidated Statements of Changes in Shareholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Redeemable Preferred Stock [Member]	Common Stock [Member] USD ($)	Additional Paid In Capital [Member] USD ($)	Retained Earnings [Member] USD ($)	Accumulated Other Comprehensive Income [Member] USD ($)	Total USD ($)
Balance at Dec. 31, 2012		$ 769	$ 1,451,965	$ 795,173	$ 3,022	$ 2,250,929
Balance (in shares) at Dec. 31, 2012	12,275	77,446,601
Increase (Decrease) in Shareholders' Equity
Repurchase of preferred stock			(22,275)			(22,275)
Repurchase of preferred stock (in shares)	(225)
Stock option activity, including tax benefit of $4,920 and $ 8,914 for the six months ended June 30, 2014 and 2013, respectively		11	48,563			48,574
Stock option activity, (in shares)		1,159,426
Restricted stock activity, including tax benefit of $840 and $677 for the six months ended June 30, 2014 and 2013, respectively			1,692			1,692
Restricted stock activity, (in shares)		248,763
Change in fair value of corporate debt securities					(1,394)	(1,394)
Foreign currency translation adjustment					(999)	(999)
Net income				53,091		53,091
Balance at Jun. 30, 2013		780	1,479,945	848,264	629	2,329,618
Balance (in shares) at Jun. 30, 2013	12,050	78,854,790
Balance at Dec. 31, 2013		775	887,556	(130,314)	383	758,400
Balance (in shares) at Dec. 31, 2013	8,624	77,788,393
Increase (Decrease) in Shareholders' Equity
Stock option activity, including tax benefit of $4,920 and $ 8,914 for the six months ended June 30, 2014 and 2013, respectively		9	19,886			19,895
Stock option activity, (in shares)		909,958
Restricted stock activity, including tax benefit of $840 and $677 for the six months ended June 30, 2014 and 2013, respectively		(3)	829			826
Restricted stock activity, (in shares)		(70,868)
Foreign currency translation adjustment					(81)	(81)
Net income				8,713		8,713
Balance at Jun. 30, 2014		$ 781	$ 908,271	$ (121,601)	$ 302	$ 787,753
Balance (in shares) at Jun. 30, 2014	8,624	78,627,483