Allowance for Loan Losses, Excluding 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
Provision for (recovery of) loan losses charged to operations	276	1,279	1,376	3,072
Loans charged off	(673)	(1,785)	(2,251)	(4,001)
Recoveries credited to allowance	403	757	860	1,104
Net (charge-offs) recoveries	(270)	(1,028)	(1,391)	(2,897)
Ending balance	20,258	23,911	20,258	23,911
Allowance Excluding Purchased Credit Impaired
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	20,138	23,305	20,169	23,322
Provision for (recovery of) loan losses charged to operations	276	1,216	1,366	3,068
Loans charged off	(673)	(1,785)	(2,251)	(4,001)
Recoveries credited to allowance	403	757	860	1,104
Net (charge-offs) recoveries	(270)	(1,028)	(1,391)	(2,897)
Ending balance	20,144	23,493	20,144	23,493
Commercial Loans | Allowance Excluding Purchased Credit Impaired
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	13,054	16,339	13,010	16,090
Provision for (recovery of) loan losses charged to operations	98	1,436	748	2,653
Loans charged off	(280)	(1,231)	(961)	(2,281)
Recoveries credited to allowance	123	203	198	285
Net (charge-offs) recoveries	(157)	(1,028)	(763)	(1,996)
Ending balance	12,995	16,747	12,995	16,747
Consumer Real Estate | Allowance Excluding Purchased Credit Impaired
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	6,446	6,393	6,489	6,597
Provision for (recovery of) loan losses charged to operations	(99)	(454)	116	31
Loans charged off	(90)	(255)	(492)	(965)
Recoveries credited to allowance	211	439	355	460
Net (charge-offs) recoveries	121	184	(137)	(505)
Ending balance	6,468	6,123	6,468	6,123
Consumer and Other | Allowance Excluding Purchased Credit Impaired
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	638	573	670	635
Provision for (recovery of) loan losses charged to operations	277	234	502	384
Loans charged off	(303)	(299)	(798)	(755)
Recoveries credited to allowance	69	115	307	359
Net (charge-offs) recoveries	(234)	(184)	(491)	(396)
Ending balance	$ 681	$ 623	$ 681	$ 623