Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Basic earnings per common share computation:
Net income per consolidated statements of income	$ 8,813	$ 9,473
Net earnings allocated to participating securities	(30)	(39)
Net earnings allocated to common stock	$ 8,783	$ 9,434
Weighted average common shares outstanding, including shares considered participating securities (in shares)	15,333,000	15,229,000
Less: Average participating securities (in shares)	(52,000)	(62,000)
Weighted average shares (in shares)	15,281,000	15,167,000
Basic earnings per common share (in dollar per share)	$ 0.57	$ 0.62
Diluted earnings per common share computation:
Net earnings allocated to common stock	$ 8,783	$ 9,434
Weighted average common shares outstanding for basic earnings per common share (in shares)	15,281,000	15,167,000
Add: Dilutive effects of assumed exercises of stock options (in shares)	0	0
Weighted average shares and dilutive potential common shares (in shares)	15,281,000	15,167,000
Diluted earnings per common share (in dollar per share)	$ 0.57	$ 0.62
Distributed earnings allocated to common stock
Basic earnings per common share computation:
Net earnings allocated to common stock	$ 2,608	$ 2,579
Undistributed earnings allocated to common stock
Basic earnings per common share computation:
Net earnings allocated to common stock	$ 6,175	$ 6,855