Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income attributable to common shareholders	$ 144,145	$ 166,738	$ 162,063	$ 169,959
Weighted average common shares outstanding - basic (in shares)	112,337	112,115	112,381	112,067
Net effect of dilutive securities:
Contingently issuable performance shares and restricted stock units (in shares)	314	356	353	415
Weighted average common shares outstanding — diluted (in shares)	112,651	112,471	112,734	112,482
Earnings per weighted-average common share outstanding
Net income attributable to common shareholders - basic (in dollars per share)	$ 1.28	$ 1.49	$ 1.44	$ 1.52
Net income attributable to common shareholders - diluted (in dollars per share)	$ 1.28	$ 1.48	$ 1.44	$ 1.51