Earnings Per Share - Calculation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share [Abstract]
Net income	$ 26,037	$ 12,989	$ 43,499	$ 28,517
Average Common Shares:
Basic (weighted-average outstanding shares) (in shares)	11,842	11,778	11,831	11,769
Dilutive potential common shares from stock options (in shares)	60	64	61	66
Diluted (weighted-average outstanding shares) (in shares)	11,902	11,842	11,892	11,835
Basic earnings per share (in dollars per share)	$ 2.20	$ 1.10	$ 3.68	$ 2.42
Diluted earnings per share (in dollars per share)	$ 2.19	$ 1.10	$ 3.66	$ 2.41