Note Investment Securities Available for Sale (Investment securities available- for-sale - Additional Information) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017		Mar. 31, 2016	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Unrealized Losses	$ 112,586			$ 112,936
Proceeds from sale of investment securities available for sale	381		$ 0
Net (loss) gain and valuation adjustments on investment securities	162		$ 0
Available For Sale Securities	9,197,527	[1]		8,209,806	[2]
COFINA
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Unrealized Losses	8,000			6,000
Available For Sale Securities	$ 15,000			$ 17,000

[1] Includes $4.9 billion pledged to secure public and trust deposits, assets sold under agreements to repurchase, credit facilities and loan servicing agreements that the secured parties are not permitted to sell or repledge the collateral, of which $4.2 billion serve as collateral for public funds.

[2] Includes $4.1 billion pledged to secure public and trust deposits, assets sold under agreements to repurchase, credit facilities and loan servicing agreements that the secured parties are not permitted to sell or repledge the collateral, of which $3.4 billion serve as collateral for public funds.