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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net income	$ 17,519	$ 20,033	$ 61,018	$ 48,550
Average Common Shares:
Basic (weighted-average outstanding shares) (in shares)	11,842	11,788	11,835	11,776
Dilutive potential common shares from stock options (in shares)	58	63	60	64
Diluted (weighted-average outstanding shares) (in shares)	11,900	11,851	11,895	11,840
Basic earnings per share (in dollars per share)	$ 1.48	$ 1.70	$ 5.16	$ 4.12
Diluted earnings per share (in dollars per share)	$ 1.47	$ 1.69	$ 5.13	$ 4.10