Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings per share — Basic:
Earnings from continuing operations	$ 75,935	$ 90,811	$ 85,917	$ 53,326	$ 11,483	$ 83,895	$ 75,721	$ 49,126	$ 305,989	$ 220,225	$ 243,275
Less: Distributed and undistributed earnings allocated to nonvested stock									(877)	(858)	(2,173)
Earnings from continuing operations available to common shareholders — Basic									$ 305,112	$ 219,367	$ 241,102
Weighted average common shares outstanding— Basic									52,814	52,536	51,617
Earnings from continuing operations per common share — Basic (in dollars per share)	$ 1.43	$ 1.71	$ 1.62	$ 1.01	$ 0.22	$ 1.60	$ 1.43	$ 0.93	$ 5.78	$ 4.18	$ 4.67
Earnings per share — Diluted:
Earnings from continuing operations	$ 75,935	$ 90,811	$ 85,917	$ 53,326	$ 11,483	$ 83,895	$ 75,721	$ 49,126	$ 305,989	$ 220,225	$ 243,275
Less: Distributed and undistributed earnings allocated to unvested stock									(872)	(853)	(2,159)
Earnings from continuing operations available to common shareholders — Diluted									$ 305,117	$ 219,372	$ 241,116
Weighted average common shares outstanding— Basic									52,814	52,536	51,617
Effect of dilutive equity awards									446	500	454
Weighted average common shares outstanding— Diluted									53,260	53,036	52,071
Earnings from continuing operations per common share — Diluted (in dollars per share)	$ 1.42	$ 1.70	$ 1.61	$ 1.00	$ 0.22	$ 1.58	$ 1.42	$ 0.92	$ 5.73	$ 4.14	$ 4.63
Anti-dilutive equity awards and market-based restrictive stock rights not included above									392	161	785