Summary of Significant Accounting Policies - Weighted-Average Common Stock Used to Calculate Basic and Diluted Earnings Per Share (Detail) - shares shares in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Weighted-average common stock for calculating basic earnings per share	24,119	24,097	24,121	24,292	24,290	24,268	24,246	24,195	24,157	24,250	24,141
Effect of potentially dilutive securities from equity-based compensation									374	373	399
Weighted-average common stock for calculating diluted earnings per share	24,453	24,443	24,471	24,738	24,697	24,632	24,579	24,540	24,531	24,623	24,540