Borrowings - Additional Information (Detail) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 1,700,000,000
Outstanding short term letters of credit	408,300,000	$ 347,500,000
Amount of maintained federal fund lines of credit with correspondent banks	504,000,000.0
Investment securities collateral for Federal Reserve Bank Discount Window Lending program	104,600,000	69,500,000
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	10,000,000.0
Outstanding amount of line of credit with correspondent bank - parent company	0	$ 0
Securities Sold under Agreements to Repurchase [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Long-term debt with variable interest rate	$ 20,200,000