Earnings Per Common Share (Computation of Earnings Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Earnings Per Share [Abstract]
Net income to common shareholders	$ 117,794	$ 121,435	$ 244,261	$ 244,913
Net income allocated to participating securities - basic and diluted	1,224	1,844	2,582	3,762
Net income allocated to common shareholders - basic and diluted	$ 116,570	$ 119,591	$ 241,679	$ 241,151
Weighted-average common shares - basic	86,096	86,067	86,057	86,362
Dilutive potential common shares	274	287	293	292
Weighted-average common shares - diluted	86,370	86,354	86,350	86,654
Earnings per common share: Basic	$ 1.35	$ 1.39	$ 2.81	$ 2.79
Earnings per common share: Diluted	$ 1.35	$ 1.38	$ 2.80	$ 2.78