Note Borrowings (Federal funds purchased and repurchase Agreements) (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	$ 710,154	$ 712,145
Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	710,154	712,145
Obligations of U.S. Government sponsored entities | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	334,408	267,074
Obligations of U.S. Government sponsored entities | Within 30 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	87,809	243,708
Obligations of U.S. Government sponsored entities | After 30 to 90 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	54,361	0
Obligations of U.S. Government sponsored entities | After 90 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	192,238	23,366
Mortgage Backed Securities | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	349,885	421,901
Mortgage Backed Securities | Within 30 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	28,340	124,878
Mortgage Backed Securities | After 30 to 90 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	57,224	154,582
Mortgage Backed Securities | After 90 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	264,321	142,441
Collateralized Mortgage Obligations | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	25,861	23,170
Collateralized Mortgage Obligations | Within 30 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	10,458	10,298
Collateralized Mortgage Obligations | After 30 to 90 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	0	12,872
Collateralized Mortgage Obligations | After 90 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	$ 15,403	$ 0