Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator [Abstract]
Net income	$ 47,346	$ 46,432	$ 43,251
Basic earnings per share [Abstract]
Weighted average shares (in shares)	17,548,000	17,431,000	17,326,000
Diluted earnings per share [Abstract]
Dilutive effect of equity grants (in shares)	18,000	52,000	71,000
Adjusted weighted average shares (in shares)	17,566,000	17,483,000	17,397,000
Earnings per share [Abstract]
Basic earnings per share (in dollars per share)	$ 2.70	$ 2.66	$ 2.50
Diluted earnings per share (in dollars per share)	$ 2.70	$ 2.66	$ 2.49
Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Options excluded from diluted calculations (in shares)	0	58,063	0