Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator [Abstract]
Net income	$ 59,228	$ 51,493	$ 47,346
Basic earnings per share [Abstract]
Weighted average shares (in shares)	17,687,000	17,631,000	17,548,000
Diluted earnings per share [Abstract]
Dilutive effect of equity grants (in shares)	16,000	22,000	18,000
Adjusted weighted average shares (in shares)	17,703,000	17,653,000	17,566,000
Earnings per share [Abstract]
Basic earnings per share (in dollars per share)	$ 3.35	$ 2.92	$ 2.70
Diluted earnings per share (in dollars per share)	$ 3.35	$ 2.92	$ 2.70
Options [Member]
Earnings Per Share [Abstract]
Options excluded from diluted calculations (in shares)	0	0	0