Indemnification Asset - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	May 09, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fdic Agreements And Fdic Indemnification Asset [Line Items]
FDIC indemnification agreement expiry month and year		2020-05
Term of FDIC indemnification agreement		10 years
True up amount payable to FDIC, description		In addition, the agreement specified that at the end of the agreement in May 2020, to the extent that total claimed losses plus servicing expenses, net of recoveries, claimed under the agreement over the entire ten year period of the agreement did not meet a certain threshold, the Company would have been required to pay to the FDIC a “true up” amount equal to fifty percent of the difference of the threshold and actual claimed losses plus servicing expenses, net of recoveries. The Company continually estimated, updated and recorded this “true up” amount, at its estimated present value, since the inception of the agreement in May 2010.
Percentage of true up amount payable to FDIC		50.00%
Payment made to FDIC	$ 184	$ (256)	$ (273)	$ 12
Gain on termination of loss share agreement	$ 712	$ (712)
Residential Real Estate Loans [Member]
Fdic Agreements And Fdic Indemnification Asset [Line Items]
FDIC indemnification agreement expiry month and year		2018-05
Nonresidential Real Estate Loans [Member]
Fdic Agreements And Fdic Indemnification Asset [Line Items]
FDIC indemnification agreement expiry month and year		2010-05