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	[1]	$ 706,857	$ (9,778)	$ 182,652	$ (138)
Stock issued for benefit plans		1,612			791	821
Stock options exercised		1,151	1	[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	[1]	999
Issuance of restricted stock			4	[1]	(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	[1]	726,956	(12,350)	281,473
Stock issued for benefit plans	[2]	1,654			354	1,300
Stock options exercised	[2]	253			253
Purchase of treasury shares	[2]	(2,636)				(2,636)
Employee stock purchase plan	[2]	1,076			1,706
Issuance of restricted stock	[2]		3	[1]	(3)
Amortization of share-based compensation	[2]	4,956			4,956
Net Income	[2]	3,570					3,570
Other comprehensive income	[2]	261						261
Ending Balance at Mar. 31, 2012	[2]	$ 1,005,643	$ 433	[1]	$ 733,592	$ (13,686)	$ 285,043	$ 261

[1] (1) $.01 par value.

[2] (2) Unaudited