Borrowings by contractual maturities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014
Debt Disclosure [Line Items]
Debt Maturities Repayments Of Principal Within Remainder Of Year	$ 1,103,708
Debt Maturities Repayments Of Principal In Year Two	789,938
Debt Maturities Repayments Of Principal In Year Three	351,112
Debt Maturities Repayments Of Principal In Year Four	79,033
Debt Maturities Repayments Of Principal In Year Five	107,203
Later years	944,491
Debt With No Stated Maturity	0
Borrowed Funds	3,375,485
Short-term Debt [Member]
Debt Disclosure [Line Items]
Debt Maturities Repayments Of Principal Within Remainder Of Year	1,200
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
Debt With No Stated Maturity	0
Borrowed Funds	1,200
Long-term Debt [Member]
Debt Disclosure [Line Items]
Debt Maturities Repayments Of Principal Within Remainder Of Year	16,701
Debt Maturities Repayments Of Principal In Year Two	329,040
Debt Maturities Repayments Of Principal In Year Three	247,105
Debt Maturities Repayments Of Principal In Year Four	79,033
Debt Maturities Repayments Of Principal In Year Five	107,203
Later years	944,491
Debt With No Stated Maturity	0
Borrowed Funds	1,723,573
Federal Funds Purchased And Securities Sold Under Agreements To Repurchase [Member]
Debt Disclosure [Line Items]
Debt Maturities Repayments Of Principal Within Remainder Of Year	1,085,807
Debt Maturities Repayments Of Principal In Year Two	460,898
Debt Maturities Repayments Of Principal In Year Three	104,007
Debt Maturities Repayments Of Principal In Year Four	0
Debt Maturities Repayments Of Principal In Year Five	0
Later years	0
Debt With No Stated Maturity	0
Borrowed Funds	$ 1,650,712