Earnings Per Share - Calculation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net income	$ 20,033	$ 17,418	$ 48,550	$ 53,338
Average Common Shares:
Basic (weighted-average outstanding shares) (in shares)	11,788	11,748	11,776	11,724
Dilutive potential common shares from stock options (in shares)	63	65	64	72
Diluted (weighted-average outstanding shares) (in shares)	11,851	11,813	11,840	11,796
Basic earnings per share (in dollars per share)	$ 1.70	$ 1.48	$ 4.12	$ 4.55
Diluted earnings per share (in dollars per share)	$ 1.69	$ 1.47	$ 4.10	$ 4.52