Description of Business and Accounting Policies - Reconciliation of Number of Shares Used in Calculation of Basic and Diluted Per Share Amounts (Detail) - shares shares in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Weighted average common shares outstanding, basic	12,640	12,607	12,577	12,550	12,473	12,310	12,152	12,102	12,594	12,260
Weighted average common shares outstanding, diluted	12,640	12,607	12,577	12,848	12,473	12,310	12,152	12,531	12,594	12,260