Loans - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Loans [Line Items]
Reverse mortgage, fair value	$ 19,800	$ 22,600
Nonaccruing loans	36,400	22,900
Potential increase in net interest income	1,800	1,200
Accrued interest receivable	19,405	17,027
Loans Receivable
Loans [Line Items]
Accrued interest receivable	15,400	13,000
First Mortgage
Loans [Line Items]
Amounts of loans serviced	102,500	124,700
Fees from servicing of loans	400	300
Value of servicing rights	400	500
First Mortgage | Maximum | Servicing Rights
Loans [Line Items]
Net losses	100
SBA Loans
Loans [Line Items]
Value of servicing rights	$ 500	$ 200