Loans Receivable and Allowance for Loan Losses - Analysis of Loans Modified in Troubled Debt Restructuring by Type of Concession (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) Loan	Jun. 30, 2017 USD ($) Loan	Jun. 30, 2018 USD ($) Loan	Jun. 30, 2017 USD ($) Loan
Financing Receivable, Modifications [Line Items]
Number of Loans | Loan	16	11	25	32
Recorded Investment | $	$ 663	$ 6,175	$ 985	$ 7,378
Extensions of maturity
Financing Receivable, Modifications [Line Items]
Number of Loans | Loan	1	2	1	3
Recorded Investment | $	$ 56	$ 5,855	$ 56	$ 6,203
Interest-rate reductions
Financing Receivable, Modifications [Line Items]
Number of Loans | Loan	15	9	24	29
Recorded Investment | $	$ 607	$ 320	$ 929	$ 1,175