Federal Home Loan Bank Advances - Additional Information (Detail)	Sep. 30, 2017	Dec. 31, 2016
Federal Home Loan Bank, Advances [Line Items]
Weighted-average rates of FHLB advances	1.40%	0.94%
Federal Home Loan Bank Advances [Member]
Federal Home Loan Bank, Advances [Line Items]
Percentage of borrowings collateralized by investment securities and residential real estate loans	143.00%

The calculated weighted average interest rate for Federal Home Loan Bank advances outstanding as of the Balance Sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13(3)(a))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant