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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income	$ 12,989	$ 20,667	$ 28,517	$ 35,920
Average Common Shares:
Basic (weighted-average outstanding shares) (in shares)	11,778	11,726	11,769	11,712
Dilutive potential common shares from stock options (in shares)	64	72	66	75
Diluted (weighted-average outstanding shares) (in shares)	11,842	11,798	11,835	11,787
Basic earnings per share (in dollars per share)	$ 1.10	$ 1.76	$ 2.42	$ 3.07
Diluted earnings per share (in dollars per share)	$ 1.10	$ 1.75	$ 2.41	$ 3.05