Long-Term Borrowings - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Maximum drawing capacity	$ 517,500,000
FHLB stock holdings	551,900
Advances outstanding	0
Residential Mortgage [Member]
Debt Instrument [Line Items]
Line of credit assets pledged as collateral	674,500,000
Revolving Line of Credit Member]
Debt Instrument [Line Items]
Maximum drawing capacity	10,000,000
Advances outstanding	$ 0
Description of variable interest rate	prime rate minus 25 basis points
Line of credit maturity year	2020