Earnings Per Share - Calculation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Net income	$ 17,462	$ 15,528
Average Common Shares:
Basic (weighted-average outstanding shares) (in shares)	11,820	11,761
Dilutive potential common shares from stock options (in shares)	62	66
Diluted (weighted-average outstanding shares) (in shares)	11,882	11,827
Basic earnings per share (in dollars per share)	$ 1.48	$ 1.32
Diluted earnings per share (in dollars per share)	$ 1.47	$ 1.31