Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings per share — Basic:
Earnings from continuing operations	$ 642,480	$ 58,913	$ 51,343	$ 38,279	$ 49,275	$ 85,138	$ 74,042	$ 56,185	$ 791,015	$ 264,640	$ 305,989
Less: Distributed and undistributed earnings allocated to unvested stock									(2,848)	(840)	(877)
Earnings from continuing operations available to common shareholders — Basic									$ 788,167	$ 263,800	$ 305,112
Weighted average common shares outstanding— Basic (in shares)									52,613	53,015	52,814
Earnings from continuing operations per common share — Basic (in dollars per share)	$ 12.21	$ 1.12	$ 0.97	$ 0.72	$ 0.93	$ 1.60	$ 1.39	$ 1.06	$ 14.98	$ 4.98	$ 5.78
Earnings per share — Diluted:
Earnings from continuing operations	$ 642,480	$ 58,913	$ 51,343	$ 38,279	$ 49,275	$ 85,138	$ 74,042	$ 56,185	$ 791,015	$ 264,640	$ 305,989
Less: Distributed and undistributed earnings allocated to unvested stock									(2,830)	(836)	(872)
Earnings from continuing operations available to common shareholders — Diluted									$ 788,185	$ 263,804	$ 305,117
Weighted average common shares outstanding— Basic (in shares)									52,613	53,015	52,814
Effect of dilutive equity awards (in shares)									375	346	446
Weighted average common shares outstanding— Diluted (in shares)									52,988	53,361	53,260
Earnings from continuing operations per common share — Diluted (in dollars per share)	$ 12.10	$ 1.11	$ 0.97	$ 0.71	$ 0.92	$ 1.59	$ 1.38	$ 1.05	$ 14.87	$ 4.94	$ 5.73
Anti-dilutive equity awards and market-based restrictive stock rights not included above (in shares)									881	716	392