Securities Held-to-Maturity - Schedule of Securities Held-to-Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Federal agency debt instruments (amortized cost)	$ 20,199	$ 21,299
Federal Agency [Member]
Schedule of Held-to-maturity Securities [Line Items]
Federal agency debt instruments (amortized cost)	$ 20,199	$ 21,299

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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