Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net income attributable to common shareholders	$ 167,443	$ 121,308	$ 190,755	$ 125,761
Weighted average common shares outstanding - basic (in shares)	111,797	111,368	111,763	111,336
Net effect of dilutive securities:
Contingently issuable performance shares and restricted stock units (in shares)	548	636	507	594
Weighted average common shares outstanding — diluted (in shares)	112,345	112,004	112,270	111,930
Earnings per weighted-average common share outstanding
Net income attributable to common shareholders - basic (in dollars per share)	$ 1.50	$ 1.09	$ 1.71	$ 1.13
Net income attributable to common shareholders - diluted (in dollars per share)	$ 1.49	$ 1.08	$ 1.70	$ 1.12