Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Dilutive shares (in shares)			0	0
Basic earnings per common share computation:
Net income per consolidated statements of income	$ 9,236	$ 7,246	$ 24,774	$ 20,409
Net earnings allocated to participating securities	(40)	(40)	(113)	(120)
Net earnings allocated to common stock	$ 9,196	$ 7,206	$ 24,661	$ 20,289
Weighted average common shares outstanding, including shares considered participating securities (in shares)	15,285,000	15,285,000	15,281,000	15,188,000
Less: Average participating securities (in shares)	(60,000)	(78,000)	(67,000)	(84,000)
Weighted average shares (in shares)	15,225,000	15,207,000	15,214,000	15,104,000
Basic earnings per common share (in dollars per share)	$ 0.60	$ 0.47	$ 1.62	$ 1.34
Diluted earnings per common share computation:
Net earnings allocated to common stock	$ 9,196	$ 7,206	$ 24,661	$ 20,289
Weighted average common shares outstanding for basic earnings per common share (in shares)	15,225,000	15,207,000	15,214,000	15,104,000
Diluted earnings per common share (in dollars per share)	$ 0.60	$ 0.47	$ 1.62	$ 1.34
Distributed earnings allocated to common stock
Basic earnings per common share computation:
Net earnings allocated to common stock	$ 2,586	$ 2,506	$ 7,607	$ 7,521
Undistributed earnings allocated to common stock
Basic earnings per common share computation:
Net earnings allocated to common stock	$ 6,610	$ 4,700	$ 17,054	$ 12,768