Condensed Consolidated Statements of Stockholders' Equity (USD $) In Thousands	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2010	$ 880,017	$ 424	$ 706,857	$ (9,778)	$ 182,652	$ (138)
Stock issued for benefit plans	1,612		791	821
Stock options exercised	1,151	1	1,150
Purchase of treasury shares	(3,393)			(3,393)
Tax benefits from stock compensation	333		333
Employee stock purchase plan	1,000	1	999
Issuance of restricted stock		4	(4)
Amortization of share-based compensation	16,830		16,830
Net Income	98,821				98,821
Other comprehensive income	138					138
Ending Balance at Dec. 31, 2011	996,509	430	726,956	(12,350)	281,473
Stock issued for benefit plans	1,654		354	1,300
Stock options exercised	523		523
Purchase of treasury shares	(2,781)			(2,781)
Tax benefits from stock compensation	126		126
Employee stock purchase plan	1,076		1,076
Issuance of restricted stock		4	(4)
Amortization of share-based compensation	14,646		14,646
Net Income	9,720				9,720
Other comprehensive income	(113)					(113)
Ending Balance at Sep. 30, 2012	$ 1,021,360	$ 434	$ 743,677	$ (13,831)	$ 291,193	$ (113)