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, 2009		$ 678,899	$ 379	[1]	$ 551,606	$ (9,221)	$ 136,358	$ (223)
Stock issued for benefit plans		1,513			242	1,271
Stock options exercised		2,087	1	[1]	2,086
Public stock offering		140,139	40	[1]	140,099
Purchase of treasury shares		(1,828)				(1,828)
Tax benefits from share based-compensation		28			28
Employee stock purchase plan		951	1	[1]	950
Issuance of restricted stock			3	[1]	(3)
Amortization of share-based compensation		11,849			11,849
Net income		46,294					46,294
Other comprehensive income		85						85
Total comprehensive income		46,379
Ending Balance at Dec. 31, 2010		880,017	424	[1]	706,857	(9,778)	182,652	(138)
Stock issued for benefit plans	[2]	1,612			791	821
Stock options exercised	[2]	990	1	[1]	989
Purchase of treasury shares	[2]	(3,289)				(3,289)
Tax benefits from share based-compensation	[2]	329			329
Employee stock purchase plan	[2]	1,000	1	[1]	999
Issuance of restricted stock	[2]		3	[1]	(3)
Amortization of share-based compensation	[2]	7,983			7,983
Net income	[2]	61,209					61,209
Other comprehensive income	[2]	348						348
Total comprehensive income	[2]	61,557
Ending Balance at Jun. 30, 2011	[2]	$ 950,199	$ 429	[1]	$ 717,945	$ (12,246)	$ 243,861	$ 210

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

[2] [2] Unaudited