Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Earnings per share - Basic:
Earnings from continuing operations	$ 62,575	$ 46,767	$ 103,377	$ 81,643
Less: Distributed and undistributed earnings allocated to nonvested stock	(556)	(590)	(978)	(1,062)
Earnings from continuing operations available to common shareholders - Basic	62,019	46,177	102,399	80,581
Weighted average common shares outstanding - Basic	51,445	50,433	51,201	50,459
Earnings from continuing operations per common share - Basic	$ 1.21	$ 0.92	$ 2.00	$ 1.60
Earnings per share - Diluted:
Earnings from continuing operations	62,575	46,767	103,377	81,643
Less: Distributed and undistributed earnings allocated to nonvested stock	(552)	(587)	(972)	(1,057)
Earnings from continuing operations available to common shareholders - Diluted	$ 62,023	$ 46,180	$ 102,405	$ 80,586
Weighted average common shares outstanding - Basic	51,445	50,433	51,201	50,459
Effect of dilutive equity awards	478	264	457	351
Weighted average common shares outstanding - Diluted	51,923	50,697	51,658	50,810
Earnings from continuing operations per common share - Diluted	$ 1.19	$ 0.91	$ 1.98	$ 1.59
Anti-dilutive equity awards and market-based restricted stock rights not included above	593	2,414	1,003	2,044