Note FDIC loss share asset (Activity in the FDIC loss share indemnification asset) (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Disclosure Activity In The F D I C Loss Share Indemnification Asset [Abstract]
Beginning Balance		$ 46,316	$ 69,334
Accretion of loss share indemnification asset, net		(934)	(776)
Credit impairment losses (reversal) to be covered under loss sharing agreements	[1]	104	148
Reimbursable expenses		537	921
Net payment from FDIC under loss-sharing agreements		(364)	0
Other adjustments attributable to FDIC loss sharing agreements		0	(5,550)
Ending Balance		45,659	64,077
Balance due to the FDIC for recoveries on covered assets		(1,190)	(5,284)
FDIC loss-share asset net		$ 44,469	$ 58,793

[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.