Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings per share — Basic:
Earnings from continuing operations	$ 108,645	$ 89,511	$ 43,519	$ 33,932	$ 643,318	$ 59,040	$ 51,395	$ 38,536	$ 275,607	$ 792,289	$ 265,232
Less: Distributed and undistributed earnings allocated to unvested stock									(998)	(2,853)	(842)
Earnings from continuing operations available to common shareholders — Basic									$ 274,609	$ 789,436	$ 264,390
Weighted average common shares outstanding— Basic (in shares)									52,390	52,613	53,015
Earnings from continuing operations per common share — Basic (in dollars per share)	$ 2.07	$ 1.70	$ 0.83	$ 0.65	$ 12.22	$ 1.12	$ 0.97	$ 0.73	$ 5.24	$ 15.00	$ 4.99
Earnings per share — Diluted:
Earnings from continuing operations	$ 108,645	$ 89,511	$ 43,519	$ 33,932	$ 643,318	$ 59,040	$ 51,395	$ 38,536	$ 275,607	$ 792,289	$ 265,232
Less: Distributed and undistributed earnings allocated to unvested stock									(995)	(2,835)	(838)
Earnings from continuing operations available to common shareholders — Diluted									$ 274,612	$ 789,454	$ 264,394
Weighted average common shares outstanding— Basic (in shares)									52,390	52,613	53,015
Effect of dilutive equity awards (in shares)									306	375	346
Weighted average common shares outstanding— Diluted (in shares)									52,696	52,988	53,361
Earnings from continuing operations per common share — Diluted (in dollars per share)	$ 2.06	$ 1.69	$ 0.82	$ 0.64	$ 12.12	$ 1.12	$ 0.97	$ 0.72	$ 5.21	$ 14.90	$ 4.95
Anti-dilutive equity awards and market-based restrictive stock rights not included above (in shares)									1,330	881	716