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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Weighted average common shares outstanding, basic	12,755	12,721	12,697	12,673	12,640	12,607	12,577	12,550	12,712	12,594
Weighted average common shares outstanding, diluted	12,755	12,721	12,697	12,673	12,640	12,607	12,577	12,848	12,712	12,594