Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net income attributable to common shareholders	$ 276,072	$ 263,027	$ 466,827	$ 388,788
Weighted average common shares outstanding - basic (in shares)	111,835	111,416	111,787	111,363
Net effect of dilutive securities:
Contingently issuable performance shares and restricted stock units (in shares)	566	684	527	624
Weighted average common shares outstanding — diluted (in shares)	112,401	112,100	112,314	111,987
Earnings per weighted-average common share outstanding
Net income attributable to common shareholders - basic (in dollars per share)	$ 2.47	$ 2.36	$ 4.18	$ 3.49
Net income attributable to common shareholders - diluted (in dollars per share)	$ 2.46	$ 2.35	$ 4.16	$ 3.47