Allowance For Loan Losses for PCI Loans, by Loan Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 20,252	$ 23,798	$ 20,227	$ 24,077
Benefit (provision) attributable to FDIC indemnification asset		138	(46)	341
Provision for (recovery of) loan losses charged to operations	276	1,279	1,376	3,072
Ending balance	20,258	23,911	20,258	23,911
Purchased Credit Impaired
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	114	493	58	755
Provision for (recovery of) PCI loan losses		(75)	56	(337)
Benefit (provision) attributable to FDIC indemnification asset		138	(46)	341
Provision for (recovery of) loan losses charged to operations		63	10	4
(Recovery of) provision for loan losses recorded through the FDIC indemnification asset		(138)	46	(341)
Ending balance	114	418	114	418
Commercial Loans | Purchased Credit Impaired
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance		8	37	77
Provision for (recovery of) PCI loan losses		8	(37)	(61)
Benefit (provision) attributable to FDIC indemnification asset			29	55
Provision for (recovery of) loan losses charged to operations		8	(8)	(6)
(Recovery of) provision for loan losses recorded through the FDIC indemnification asset			(29)	(55)
Ending balance		16		16
Consumer Real Estate | Purchased Credit Impaired
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	114	485	21	678
Provision for (recovery of) PCI loan losses		(83)	93	(276)
Benefit (provision) attributable to FDIC indemnification asset		138	(75)	286
Provision for (recovery of) loan losses charged to operations		55	18	10
(Recovery of) provision for loan losses recorded through the FDIC indemnification asset		(138)	75	(286)
Ending balance	$ 114	$ 402	$ 114	$ 402