Note FDIC loss share asset (Activity in the FDIC loss share indemnification asset) (Detail) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
		Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2017		Sep. 30, 2016		Dec. 31, 2016
Disclosure Activity In The F D I C Loss Share Indemnification Asset [Abstract]
Beginning Balance		$ 53,070		$ 218,122		$ 69,334		$ 310,221
Accretion of loss share indemnification asset, net		567		(1,259)		(62)		(9,337)
Credit impairment losses (reversal) to be covered under loss sharing agreements	[1]	(329)		659		1,945		(959)
Reimbursable expenses		588		853		2,232		7,038
Net payment from FDIC under loss-sharing agreements		(4,502)		(10,897)		(18,505)		(99,485)
Arbitration decision charge		0		(54,924)		0		(54,924)
Other adjustments attributable to FDIC loss sharing agreements		0		(87)		(5,550)		(87)
Ending Balance		49,394		152,467		49,394		152,467
Balance due to the FDIC for recoveries on covered assets		(924)	[2]	(7,080)	[2]	(924)	[2]	(7,080)	[2]	$ (27,600)
FDIC loss-share asset net		$ 48,470		$ 145,387		$ 48,470		$ 145,387

[1] Reductions in expected cash flows for ASC 310-30 loans, which may impact the provision for loan losses, may consider reductions in both principal and interest cash flow expectations. The amount covered under the FDIC loss-sharing agreements for interest not collected from borrowers is limited under the agreements (approximately 90 days); accordingly, these amounts are not subject fully to the 80% mirror accounting.

[2] Balance due to the FDIC for recoveries on covered assets for the quarter and nine months ended September 30, 2016 amounting to $ 7.1 million was included in other liabilities in the accompanying Consolidated Statement of Condition (December 31, 2016 - $27.6 million).