Stockholders' Equity - Treasury Stock (Detail) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2018	Aug. 31, 2018	Feb. 28, 2018
Equity, Class of Treasury Stock [Line Items]
Shares purchased during period (shares)	36,542	501,782	127,792
Total number of shares purchased (shares)	666,116			666,116
Average price paid per share (usd per share)	$ 15.25	$ 14.99	$ 15.04
Average price paid per share (usd per share)	$ 15.01			$ 15.01
Treasury stock acquired during period				$ 10,026,000
Commissions paid to acquire shares				$ 26,645
Stock repurchase authority					$ 10,000,000.0	$ 10,000,000.0
Common Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Shares purchased during period (shares)	36,542	501,782	127,792
Total number of shares purchased (shares)	666,116			666,116
Treasury stock acquired during period	$ 10,000,000	$ 558,000	$ 8,077,000