Earnings Per Share - Calculation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income	$ 101,510	$ 97,446	$ 173,979	$ 176,611
Income attributable to unvested participating securities, basic EPS	(437)	(428)	(747)	(835)
Net income used in calculating basic EPS	$ 101,073	$ 97,018	$ 173,232	$ 175,776
Weighted-average vested shares	40,132	42,483	40,632	42,653
Basic EPS	$ 2.52	$ 2.28	$ 4.26	$ 4.12
Income attributable to unvested participating securities, diluted EPS	$ (436)	$ (427)	$ (746)	$ (833)
Net income used in calculating diluted EPS	$ 101,074	$ 97,019	$ 173,233	$ 175,778
Dilutive effect of incremental shares to be issued for contingently-issuable shares	114	136	111	127
Weighted-average shares used in calculating diluted EPS	40,246	42,619	40,743	42,780
Diluted EPS	$ 2.51	$ 2.28	$ 4.25	$ 4.11