Earnings Per Common Share (Computation of Earnings Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Earnings Per Share [Abstract]
Net income to common shareholders	$ 97,738	$ 135,389	$ 341,999	$ 380,302
Net income allocated to participating securities - basic and diluted	992	2,014	3,574	5,776
Net income allocated to common shareholders - basic	96,746	133,375	338,425	374,526
Net income allocated to common shareholders - diluted	$ 96,746	$ 133,375	$ 338,425	$ 374,526
Weighted-average common shares - basic	86,131	85,706	86,082	86,141
Dilutive potential common shares	306	314	286	298
Weighted-average common shares - diluted	86,437	86,020	86,368	86,439
Earnings per common share: Basic	$ 1.12	$ 1.56	$ 3.93	$ 4.35
Earnings per common share: Diluted	$ 1.12	$ 1.55	$ 3.92	$ 4.33