Allowance For Loan Losses for PCI Loans, by Loan Segment (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 24,077	$ 25,770	$ 26,205
Purchased impaired provision	(277)	8,659
Benefit attributable to FDIC indemnification asset	422	(451)
(Recovery of) provision for loan losses charged to operations	145	8,208	5,678
Provision for loan losses recorded through the FDIC indemnification asset	145	8,208	5,678
Ending balance	20,227	24,077	25,770
Purchased Credit Impaired
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	755	8	201
Purchased impaired provision	(697)	747
Benefit attributable to FDIC indemnification asset	422	(451)
(Recovery of) provision for loan losses charged to operations	(275)	296	(193)
Provision for loan losses recorded through the FDIC indemnification asset	422	451
Ending balance	58	755	8
Commercial Loans | Purchased Credit Impaired
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	77	8	201
Purchased impaired provision	(40)	69
Benefit attributable to FDIC indemnification asset	26	(55)
(Recovery of) provision for loan losses charged to operations	(14)	14	(193)
Provision for loan losses recorded through the FDIC indemnification asset	26	55
Ending balance	37	77	8
Consumer Real Estate | Purchased Credit Impaired
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	678
Purchased impaired provision	(657)	678
Benefit attributable to FDIC indemnification asset	396	(396)
(Recovery of) provision for loan losses charged to operations	(261)	282
Provision for loan losses recorded through the FDIC indemnification asset	396	396
Ending balance	$ 21	$ 678