Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net income attributable to common shareholders	$ 63,981	$ 312,276	$ 144,145	$ 17,918	$ 26,076	$ 315,012	$ 166,738	$ 3,221	$ 538,320	$ 511,047	$ 488,456
Weighted Average common shares outstanding — basic (in shares)									112,443	112,129	111,839
Net effect of dilutive securities:
Contingently issuable performance shares and restricted stock units (in shares)									315	421	528
Weighted average common shares outstanding — diluted (in shares)									112,758	112,550	112,367
Earnings per weighted-average common share outstanding
Net income attributable to common shareholders - basic (in dollars per share)	$ 0.57	$ 2.78	$ 1.28	$ 0.16	$ 0.23	$ 2.81	$ 1.49	$ 0.03	$ 4.79	$ 4.56	$ 4.37
Net Income attributable to common shareholders - diluted (in dollars per share)	$ 0.57	$ 2.77	$ 1.28	$ 0.16	$ 0.23	$ 2.80	$ 1.48	$ 0.03	$ 4.77	$ 4.54	$ 4.35