Note Borrowings (Federal funds purchased and repurchase Agreements) (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	$ 434,714	$ 479,425
Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	434,714	479,425
US Treasury Securities | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	223,107	52,519
US Treasury Securities | Within 30 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	103,338	32,700
US Treasury Securities | After 30 to 90 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	12,415	0
US Treasury Securities | After 90 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	107,354	19,819
Obligations of U.S. Government sponsored entities | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	123,960	263,399
Obligations of U.S. Government sponsored entities | Within 30 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	15,963	95,720
Obligations of U.S. Government sponsored entities | After 30 to 90 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	75,368	142,299
Obligations of U.S. Government sponsored entities | After 90 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	32,629	25,380
Mortgage Backed Securities | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	80,551	152,220
Mortgage Backed Securities | Within 30 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	55,817	39,108
Mortgage Backed Securities | After 30 to 90 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	24,734	58,552
Mortgage Backed Securities | After 90 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	0	54,560
Collateralized Mortgage Obligations | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	7,096	11,287
Collateralized Mortgage Obligations | Within 30 days | Secured Debt
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase liability	$ 7,096	$ 11,287