Earnings Per Common Share (Computation of Earnings Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Earnings Per Share [Abstract]
Net income to common shareholders	$ 123,478	$ 107,172
Net income allocated to participating securities - basic and diluted	1,918	2,337
Net income allocated to common shareholders - basic and diluted	$ 121,560	$ 104,835
Weighted-average common shares - basic	86,660	86,752
Dilutive potential common shares	276	53
Weighted-average common shares - diluted	86,936	86,805
Earnings per common share: Basic	$ 1.40	$ 1.21
Earnings per common share: Diluted	$ 1.40	$ 1.21