Earnings Per Common Share - Computation of basic and diluted earnings per common share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021
Basic Earnings Per Share:
Net income available to common shareholders	$ 22,360	$ 26,357	$ 31,385	$ 40,996	$ 48,717	$ 72,381
Less: income allocated to participating securities	17		39		54	104
Net income allocated to common shareholders	$ 22,343		$ 31,346		$ 48,663	$ 72,277
Weighted average common shares outstanding including participating securities	35,608		37,322		35,816	37,327
Less: Participating securities	27		46		40	53
Average common shares	35,581		37,276		35,776	37,274
Basic earnings per common share	$ 0.63		$ 0.84		$ 1.36	$ 1.94
Diluted Earnings Per Share:
Net income allocated to common shareholders	$ 22,343		$ 31,346		$ 48,663	$ 72,277
Weighted average common shares outstanding for basic earnings per common share	35,581		37,276		35,776	37,274
Add: Dilutive effects of stock options and restricted stock units	101		82		104	77
Average shares and dilutive potential common shares	35,682		37,358		35,880	37,351
Diluted earnings per common share	$ 0.63		$ 0.84		$ 1.36	$ 1.94