Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator [Abstract]
Net income	$ 59,504	$ 64,540	$ 59,228
Basic earnings per share [Abstract]
Weighted average shares (in shares)	17,748,000	17,724,000	17,687,000
Diluted earnings per share [Abstract]
Dilutive effect of equity grants (in shares)	8,000	16,000	16,000
Adjusted weighted average shares (in shares)	17,756,000	17,740,000	17,703,000
Earnings per share [Abstract]
Basic earnings per share (in dollars per share)	$ 3.35	$ 3.64	$ 3.35
Diluted earnings per share (in dollars per share)	$ 3.35	$ 3.64	$ 3.35
Options [Member]
Earnings Per Share [Abstract]
Options excluded from diluted calculations (in shares)	0	0	0