Allowance for Loan and Lease Losses - Summary of Allowance for Loan and Lease Losses and Recorded Investment in Loans by Class of Loans and by Impairment Evaluation (Detail) - USD ($) $ in Thousands	Mar. 31, 2016		Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans collectively evaluated for impairment, unamortized purchase discounts (Premium)	$ 7,500		$ 8,100
Acquired Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans, Collectively Evaluated for Impairment	269,400		284,800
Non-PCI Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	93		75
Allowance for Loan Losses, Collectively Evaluated for Impairment	20,691		20,471
Loans, Individually Evaluated for Impairment	13,938		10,692
Loans, Collectively Evaluated for Impairment	4,604,532	[1]	4,544,147	[2]
Non-PCI Loans | Total commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	21		0
Allowance for Loan Losses, Collectively Evaluated for Impairment	3,692		3,829
Loans, Individually Evaluated for Impairment	875		463
Loans, Collectively Evaluated for Impairment	835,869	[1]	821,498	[2]
Non-PCI Loans | Total commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0
Allowance for Loan Losses, Collectively Evaluated for Impairment	9,396		8,995
Loans, Individually Evaluated for Impairment	10,393		6,765
Loans, Collectively Evaluated for Impairment	2,179,336	[1]	2,118,061	[2]
Non-PCI Loans | Total consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	72		75
Allowance for Loan Losses, Collectively Evaluated for Impairment	7,363		7,414
Loans, Individually Evaluated for Impairment	2,670		3,464
Loans, Collectively Evaluated for Impairment	1,462,487	[1]	1,487,324	[2]
Non-PCI Loans | Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0
Allowance for Loan Losses, Collectively Evaluated for Impairment	240		233
Loans, Individually Evaluated for Impairment	0		0
Loans, Collectively Evaluated for Impairment	126,840	[1]	117,264	[2]
Non-PCI Loans | Non-owner occupied commercial real estate | Total commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0
Allowance for Loan Losses, Collectively Evaluated for Impairment	1,238		1,282
Loans, Individually Evaluated for Impairment	775		463
Loans, Collectively Evaluated for Impairment	569,650	[1]	563,177	[2]
Non-PCI Loans | Other commercial construction and land | Total commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	21		0
Allowance for Loan Losses, Collectively Evaluated for Impairment	1,613		1,735
Loans, Individually Evaluated for Impairment	100		0
Loans, Collectively Evaluated for Impairment	118,369	[1]	110,918	[2]
Non-PCI Loans | Multifamily commercial real estate | Total commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0
Allowance for Loan Losses, Collectively Evaluated for Impairment	46		59
Loans, Individually Evaluated for Impairment	0		0
Loans, Collectively Evaluated for Impairment	53,989	[1]	57,099	[2]
Non-PCI Loans | 1-4 family residential construction and land | Total commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0
Allowance for Loan Losses, Collectively Evaluated for Impairment	795		753
Loans, Individually Evaluated for Impairment	0		0
Loans, Collectively Evaluated for Impairment	93,861	[1]	90,304	[2]
Non-PCI Loans | Owner occupied commercial real estate | Total commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0
Allowance for Loan Losses, Collectively Evaluated for Impairment	1,396		1,338
Loans, Individually Evaluated for Impairment	4,358		3,858
Loans, Collectively Evaluated for Impairment	887,647	[1]	891,137	[2]
Non-PCI Loans | Commercial and industrial loans | Total commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0
Allowance for Loan Losses, Collectively Evaluated for Impairment	8,000		7,657
Loans, Individually Evaluated for Impairment	6,035		2,907
Loans, Collectively Evaluated for Impairment	1,290,601	[1]	1,225,668	[2]
Non-PCI Loans | Lease financing | Total commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0		0
Allowance for Loan Losses, Collectively Evaluated for Impairment	0		0
Loans, Individually Evaluated for Impairment	0		0
Loans, Collectively Evaluated for Impairment	1,088	[1]	1,256	[2]
Non-PCI Loans | 1-4 family residential | Total consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	45		46
Allowance for Loan Losses, Collectively Evaluated for Impairment	2,131		2,225
Loans, Individually Evaluated for Impairment	1,459		1,468
Loans, Collectively Evaluated for Impairment	768,934	[1]	755,771	[2]
Non-PCI Loans | Home equity loans | Total consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	13		12
Allowance for Loan Losses, Collectively Evaluated for Impairment	537		581
Loans, Individually Evaluated for Impairment	810		1,573
Loans, Collectively Evaluated for Impairment	294,739	[1]	298,719	[2]
Non-PCI Loans | Other consumer loans | Total consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	14		17
Allowance for Loan Losses, Collectively Evaluated for Impairment	4,695		4,608
Loans, Individually Evaluated for Impairment	401		423
Loans, Collectively Evaluated for Impairment	398,814	[1]	432,834	[2]
Purchased Credit- Impaired | Non-PCI Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Purchased Credit-Impaired	24,479		24,488
Loans, Purchase Credit-Impaired	1,008,417		1,067,308
Purchased Credit- Impaired | Non-PCI Loans | Total commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Purchased Credit-Impaired	12,621		12,149
Loans, Purchase Credit-Impaired	381,433		415,176
Purchased Credit- Impaired | Non-PCI Loans | Total commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Purchased Credit-Impaired	2,420		2,137
Loans, Purchase Credit-Impaired	282,052		291,106
Purchased Credit- Impaired | Non-PCI Loans | Total consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Purchased Credit-Impaired	9,376		10,172
Loans, Purchase Credit-Impaired	312,325		328,188
Purchased Credit- Impaired | Non-PCI Loans | Other
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Purchased Credit-Impaired	62		30
Loans, Purchase Credit-Impaired	32,607		32,838
Purchased Credit- Impaired | Non-PCI Loans | Non-owner occupied commercial real estate | Total commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Purchased Credit-Impaired	433		316
Loans, Purchase Credit-Impaired	280,341		302,752
Purchased Credit- Impaired | Non-PCI Loans | Other commercial construction and land | Total commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Purchased Credit-Impaired	11,562		11,184
Loans, Purchase Credit-Impaired	76,502		85,877
Purchased Credit- Impaired | Non-PCI Loans | Multifamily commercial real estate | Total commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Purchased Credit-Impaired	136		127
Loans, Purchase Credit-Impaired	21,748		23,609
Purchased Credit- Impaired | Non-PCI Loans | 1-4 family residential construction and land | Total commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Purchased Credit-Impaired	490		522
Loans, Purchase Credit-Impaired	2,842		2,938
Purchased Credit- Impaired | Non-PCI Loans | Owner occupied commercial real estate | Total commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Purchased Credit-Impaired	291		167
Loans, Purchase Credit-Impaired	203,455		209,977
Purchased Credit- Impaired | Non-PCI Loans | Commercial and industrial loans | Total commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Purchased Credit-Impaired	2,129		1,970
Loans, Purchase Credit-Impaired	78,597		81,129
Purchased Credit- Impaired | Non-PCI Loans | Lease financing | Total commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Purchased Credit-Impaired	0		0
Loans, Purchase Credit-Impaired	0		0
Purchased Credit- Impaired | Non-PCI Loans | 1-4 family residential | Total consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Purchased Credit-Impaired	8,198		8,786
Loans, Purchase Credit-Impaired	236,608		249,983
Purchased Credit- Impaired | Non-PCI Loans | Home equity loans | Total consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Purchased Credit-Impaired	1,045		1,260
Loans, Purchase Credit-Impaired	72,961		74,984
Purchased Credit- Impaired | Non-PCI Loans | Other consumer loans | Total consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses, Purchased Credit-Impaired	133		126
Loans, Purchase Credit-Impaired	$ 2,756		$ 3,221

[1] Loans collectively evaluated for impairment include $269.4 million of acquired loans which are presented net of unamortized purchase discounts of $7.5 million.

[2] Loans collectively evaluated for impairment include $284.8 million of acquired loans which are presented net of unamortized purchase discounts of $8.1 million.