Earnings Per Common Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Basic earnings per common share computation:
Net earnings allocated to common stock	$ 13,106	$ 8,813
Net earnings allocated to participating securities	(45)	(30)
Net earnings allocated to common stock	$ 13,061	$ 8,783
Weighted average common shares outstanding, including shares considered participating securities (in shares)	16,855,000	15,333,000
Less: Average participating securities (in shares)	(56,000)	(52,000)
Weighted average shares (in shares)	16,799,000	15,281,000
Basic earnings per common share (in dollar per share)	$ 0.78	$ 0.57
Diluted earnings per common share computation:
Net earnings allocated to common stock	$ 13,061	$ 8,783
Weighted average common shares outstanding for basic earnings per common share (in shares)	16,799,000	15,281,000
Add: Dilutive effects of performance based-shares (in shares)	0	0
Weighted average shares and dilutive potential common shares (in shares)	16,799,000	15,281,000
Diluted earnings per common share (in dollar per share)	$ 0.78	$ 0.57
Distributed earnings allocated to common stock
Basic earnings per common share computation:
Net earnings allocated to common stock	$ 2,859	$ 2,608
Undistributed earnings allocated to common stock
Basic earnings per common share computation:
Net earnings allocated to common stock	$ 10,202	$ 6,175