Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net income	$ 87,651	$ 80,459	$ 48,283
Denominator:
Weighted-average shares outstanding - basic (in shares)	18,374,000	18,154,000	17,991,000
Effect of dilutive shares (in shares)	285,000	393,000	232,000
Weighted-average shares outstanding - diluted (in shares)	18,659,000	18,547,000	18,223,000
Basic earnings per share (in dollars per share)	$ 4.77	$ 4.43	$ 2.68
Diluted earnings per share (in dollars per share)	$ 4.70	$ 4.34	$ 2.65
Antidilutive securities excluded from computation of earnings per share (shares)	36,642	0	0