Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings per share - Basic:
Earnings from continuing operations	$ 64,311	$ 56,933	$ 145,954	$ 123,704
Less: Distributed and undistributed earnings allocated to nonvested stock	(814)	(933)	(1,891)	(1,981)
Earnings from continuing operations available to common shareholders - Basic	63,497	56,000	144,063	121,723
Weighted average common shares outstanding - Basic	50,381	50,426	50,433	50,533
Earnings from continuing operations per common share - Basic	$ 1.26	$ 1.11	$ 2.86	$ 2.41
Earnings per share - Diluted:
Earnings from continuing operations	64,311	56,933	145,954	123,704
Less: Distributed and undistributed earnings allocated to nonvested stock	(812)	(928)	(1,883)	(1,972)
Earnings from continuing operations available to common shareholders - Diluted	$ 63,499	$ 56,005	$ 144,071	$ 121,732
Weighted average common shares outstanding - Basic	50,381	50,426	50,433	50,533
Effect of dilutive equity awards	172	327	292	389
Weighted average common shares outstanding - Diluted	50,553	50,753	50,725	50,922
Earnings from continuing operations per common share - Diluted	$ 1.26	$ 1.10	$ 2.84	$ 2.39
Anti-dilutive equity awards and market-based restricted stock rights not included above	2,613	1,718	2,234	1,462