Computation of Earnings Per Share - Calculation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator
Net income	$ 9,054	$ 6,278	$ 21,318	$ 11,952
Determination of shares
Weighted-average common shares outstanding	5,025	5,104	5,038	5,113
Dilutive effect - share-based awards	113	16	50	16
Diluted weighted-average common shares outstanding	5,138	5,120	5,088	5,129
Earnings per common share
Basic	$ 1.80	$ 1.23	$ 4.23	$ 2.34
Diluted	$ 1.76	$ 1.23	$ 4.19	$ 2.33