Note Borrowings (Federal funds purchased and repurchase Agreements) (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	$ 821,604	$ 712,145
Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	821,604	712,145
US Treasury Securities | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	82,003	0
US Treasury Securities | After 90 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	82,003	0
Obligations of U.S. Government sponsored entities | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	364,092	267,074
Obligations of U.S. Government sponsored entities | Within 30 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	109,248	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	84,993	0
Obligations of U.S. Government sponsored entities | After 90 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	169,851	23,366
Mortgage Backed Securities | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	350,697	421,901
Mortgage Backed Securities | Within 30 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	31,117	124,878
Mortgage Backed Securities | After 30 to 90 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	81,489	154,582
Mortgage Backed Securities | After 90 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	238,091	142,441
Collateralized Mortgage Obligations | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	24,812	23,170
Collateralized Mortgage Obligations | Within 30 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	9,991	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	$ 14,821	$ 0