Federal Home Loan Bank Advances - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2014	Dec. 31, 2016	Nov. 18, 2014
Federal Home Loan Bank Advances [Line Items]
Remaining credit available for collateral with FHLB	$ 256,800		$ 172,100
Minimum ratio required of collateral to advances for one-to-four-family loans	120.00%
Modified fixed rate term advances				$ 50,000
Weighted average maturity period, fixed		2 years
Weighted average maturity period, floating		5 years
Amortized modified borrowing	5 years
Amount of prepayment penalty	$ 307		$ 786	$ 3,900
Effective rate on modified borrowings	3.26%		2.73%
Fixed Rate [Member]
Federal Home Loan Bank Advances [Line Items]
Interest rate		4.20%
Floating Rate [Member]
Federal Home Loan Bank Advances [Line Items]
Interest rate	1.70%		1.16%