Borrowings by contractual maturities (Detail) $ in Thousands	Jun. 30, 2015 USD ($)
Debt Disclosure [Line Items]
Debt Maturities Repayments Of Principal Within Remainder Of Year	$ 1,212,222
Debt Maturities Repayments Of Principal In Year Two	582,274
Debt Maturities Repayments Of Principal In Year Three	85,645
Debt Maturities Repayments Of Principal In Year Four	109,494
Debt Maturities Repayments Of Principal In Year Five	465,813
Later years	571,024
Borrowed Funds	3,026,472
Short-term Debt [Member]
Debt Disclosure [Line Items]
Debt Maturities Repayments Of Principal Within Remainder Of Year	101,200
Debt Maturities Repayments Of Principal In Year Two	0
Debt Maturities Repayments Of Principal In Year Three	0
Debt Maturities Repayments Of Principal In Year Four	0
Debt Maturities Repayments Of Principal In Year Five	0
Later years	0
Borrowed Funds	101,200
Long-term Debt [Member]
Debt Disclosure [Line Items]
Debt Maturities Repayments Of Principal Within Remainder Of Year	318,516
Debt Maturities Repayments Of Principal In Year Two	253,536
Debt Maturities Repayments Of Principal In Year Three	85,645
Debt Maturities Repayments Of Principal In Year Four	109,494
Debt Maturities Repayments Of Principal In Year Five	465,813
Later years	571,024
Borrowed Funds	1,804,028
Federal Funds Purchased And Securities Sold Under Agreements To Repurchase [Member]
Debt Disclosure [Line Items]
Debt Maturities Repayments Of Principal Within Remainder Of Year	792,506
Debt Maturities Repayments Of Principal In Year Two	328,738
Debt Maturities Repayments Of Principal In Year Three	0
Debt Maturities Repayments Of Principal In Year Four	0
Debt Maturities Repayments Of Principal In Year Five	0
Later years	0
Borrowed Funds	$ 1,121,244