Earnings Per Share - Calculation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net income	$ 112,101	$ 96,223	$ 286,080	$ 272,834
Income attributable to unvested participating securities, basic EPS	(493)	(415)	(1,239)	(1,251)
Net income used in calculating basic EPS	$ 111,608	$ 95,808	$ 284,841	$ 271,583
Weighted-average vested shares	39,588	41,964	40,281	42,420
Basic EPS	$ 2.82	$ 2.28	$ 7.07	$ 6.40
Income attributable to unvested participating securities, diluted EPS	$ (492)	$ (413)	$ (1,236)	$ (1,248)
Net income used in calculating diluted EPS	$ 111,609	$ 95,810	$ 284,844	$ 271,586
Dilutive effect of incremental shares to be issued for contingently-issuable shares	122	136	115	130
Weighted-average shares used in calculating diluted EPS	39,710	42,100	40,396	42,550
Diluted EPS	$ 2.81	$ 2.28	$ 7.05	$ 6.38