Stock Repurchase Program - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2008	Dec. 31, 2007
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program			$ 23,100,000	$ 5,000,000
Stock repurchase program expiration date	Sep. 22, 2017
Repurchase of common stock	151,000	0
Aggregate purchase price common stock	$ 948,000
Remaining authorized repurchase amount	$ 6,500,000
Prior Stock Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program expiration date	Sep. 21, 2018