Earnings Per Common Share (Computation of Basic and Diluted Earnings per Common Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Numerator:
Net income	$ 64,207	$ 87,850	$ 65,764	$ 67,150	$ 125,255	$ 86,941	$ 103,974	$ 98,814	$ 284,971	$ 414,984	$ 197,853
Distributed and undistributed earnings allocated to participating securities									(5,075)	(5,991)	(8,882)
Income allocated to common stockholders for basic earnings per common share									$ 279,896	$ 408,993	$ 188,971
Denominator:
Weighted average common shares outstanding									80,032,356	91,612,243	92,869,736
Less average unvested stock awards									(1,224,568)	(1,212,055)	(1,163,480)
Weighted Average Number of Shares Outstanding, Basic, Total									78,807,788	90,400,188	91,706,256
Basic earnings per common share	$ 0.83	$ 1.13	$ 0.82	$ 0.79	$ 1.42	$ 0.94	$ 1.12	$ 1.06	$ 3.55	$ 4.52	$ 2.06
Numerator:
Income allocated to common stockholders for basic earnings per common share									$ 279,896	$ 408,993	$ 188,971
Adjustment for earnings reallocated from participating securities									(626)	(585)	(123)
Income used in calculating diluted earnings per common share									$ 279,270	$ 408,408	$ 188,848
Denominator:
Weighted Average Number of Shares Outstanding, Basic, Total									78,807,788	90,400,188	91,706,256
Dilutive effect of certain share-based awards									94	134	24,608
Weighted average shares for diluted earnings per common share									78,807,882	90,400,322	91,730,864
Diluted earnings per common share	$ 0.82	$ 1.12	$ 0.82	$ 0.79	$ 1.41	$ 0.94	$ 1.11	$ 1.06	$ 3.54	$ 4.52	$ 2.06