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		1,654	[2]			354	[2]	1,300	[2]
Stock options exercised		375	[2]			375	[2]
Purchase of treasury shares		(2,686)	[2]					(2,686)	[2]
Tax benefits from stock compensation		126	[2]			126	[2]
Employee stock purchase plan		1,076	[2]			1,076	[2]
Issuance of restricted stock			[2]	4	[1],[2]	(4)	[2]
Amortization of share-based compensation		10,035	[2]			10,035	[2]
Net Income		6,598	[2]							6,598	[2]
Other comprehensive income		0	[2]
Ending Balance at Jun. 30, 2012	[2]	$ 1,013,687		$ 434	[1]	$ 738,918		$ (13,736)		$ 288,071

[1] $0.01 par value.

[2] Unaudited