Borrowings - Additional Information (Detail) - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 1,300,000,000
Outstanding short term letters of credit	104,900,000	$ 148,500,000
Amount of maintained federal fund lines of credit with correspondent banks	367,000,000	302,000,000
Investment securities collateral for Federal Reserve Bank line of credit	55,500,000	55,700,000
Outstanding amount of federal fund line of credit with Federal Reserve Bank of Philadelphia	0	$ 0
Amount of maintained line of credit with correspondent bank - parent company	10,000,000
Outstanding amount of line of credit with correspondent bank - parent company	0
Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Long-term debt with call option	50,500,000
Securities Sold under Agreements to Repurchase [Member]
Debt Instrument [Line Items]
Long-term debt with fixed interest rate	5,200,000
Securities Sold under Agreements to Repurchase [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Long-term debt with variable interest rate	$ 25,800,000