Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings per share — Basic:
Earnings from continuing operations	$ 49,275	$ 85,138	$ 74,042	$ 56,185	$ 75,935	$ 90,811	$ 85,917	$ 53,326	$ 264,640	$ 305,989	$ 220,225
Less: Distributed and undistributed earnings allocated to unvested stock									(840)	(877)	(858)
Earnings from continuing operations available to common shareholders — Basic									$ 263,800	$ 305,112	$ 219,367
Weighted average common shares outstanding— Basic (in shares)									53,015	52,814	52,536
Earnings from continuing operations per common share — Basic (in dollars per share)	$ 0.93	$ 1.60	$ 1.39	$ 1.06	$ 1.43	$ 1.71	$ 1.62	$ 1.01	$ 4.98	$ 5.78	$ 4.18
Earnings per share — Diluted:
Earnings from continuing operations	$ 49,275	$ 85,138	$ 74,042	$ 56,185	$ 75,935	$ 90,811	$ 85,917	$ 53,326	$ 264,640	$ 305,989	$ 220,225
Less: Distributed and undistributed earnings allocated to unvested stock									(836)	(872)	(853)
Earnings from continuing operations available to common shareholders — Diluted									$ 263,804	$ 305,117	$ 219,372
Weighted average common shares outstanding— Basic (in shares)									53,015	52,814	52,536
Effect of dilutive equity awards (in shares)									346	446	500
Weighted average common shares outstanding— Diluted (in shares)									53,361	53,260	53,036
Earnings from continuing operations per common share — Diluted (in dollars per share)	$ 0.92	$ 1.59	$ 1.38	$ 1.05	$ 1.42	$ 1.70	$ 1.61	$ 1.00	$ 4.94	$ 5.73	$ 4.14
Anti-dilutive equity awards and market-based restrictive stock rights not included above (in shares)									716	392	161