Earnings Per Share - Calculation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net income	$ 93,557	$ 96,223	$ 97,446	$ 79,165	$ 86,541	$ 85,139	$ 86,700	$ 65,715	$ 366,391	$ 324,094	$ 350,255
Income attributable to unvested participating securities, basic EPS									(1,654)	(1,893)	(2,526)
Net income used in calculating basic EPS									$ 364,737	$ 322,201	$ 347,729
Weighted-average vested shares									42,181	43,854	45,598
Basic EPS	$ 2.25	$ 2.28	$ 2.28	$ 1.84	$ 1.99	$ 1.95	$ 1.96	$ 1.46	$ 8.65	$ 7.35	$ 7.63
Income attributable to unvested participating securities, diluted EPS									$ (1,650)	$ (1,888)	$ (2,521)
Net income used in calculating diluted EPS									$ 364,741	$ 322,206	$ 347,734
Dilutive effect of incremental shares to be issued for contingently-issuable shares									133	131	91
Weighted-average shares used in calculating diluted EPS									42,314	43,985	45,689
Diluted EPS	$ 2.24	$ 2.28	$ 2.28	$ 1.83	$ 1.99	$ 1.94	$ 1.95	$ 1.46	$ 8.62	$ 7.33	$ 7.61