Loans - Major Categories of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	$ 5,634,957	$ 5,559,214
Covered loans		73,502
Total commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,218,177	1,237,014
Covered loans		123
Total commercial real estate | Non-owner occupied commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	850,766	866,392
Covered loans		0
Total commercial real estate | Other commercial construction and land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	194,971	196,672
Covered loans		123
Total commercial real estate | Multifamily commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	75,737	80,708
Covered loans		0
Total commercial real estate | 1-4 family residential construction and land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	96,703	93,242
Covered loans		0
Total commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	2,471,781	2,415,865
Covered loans		67
Total commercial | Owner occupied commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,095,460	1,104,905
Covered loans		67
Total commercial | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,375,233	1,309,704
Covered loans		0
Total commercial | Lease financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,088	1,256
Covered loans		0
Total consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,785,552	1,756,233
Covered loans		73,312
Total consumer | 1-4 family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,015,071	976,904
Covered loans		40,887
Total consumer | Home equity loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	368,510	342,851
Covered loans		32,425
Total consumer | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	401,971	436,478
Covered loans		0
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	159,447	150,102
Covered loans		0
Non-PCI Loans, New
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	4,354,791	4,278,181
Covered loans		0
Non-PCI Loans, New | Total commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	789,241	769,992
Covered loans		0
Non-PCI Loans, New | Total commercial real estate | Non-owner occupied commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	528,675	517,559
Covered loans		0
Non-PCI Loans, New | Total commercial real estate | Other commercial construction and land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	118,279	110,716
Covered loans		0
Non-PCI Loans, New | Total commercial real estate | Multifamily commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	48,426	51,413
Covered loans		0
Non-PCI Loans, New | Total commercial real estate | 1-4 family residential construction and land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	93,861	90,304
Covered loans		0
Non-PCI Loans, New | Total commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	2,148,324	2,081,644
Covered loans		0
Non-PCI Loans, New | Total commercial | Owner occupied commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	856,384	858,068
Covered loans		0
Non-PCI Loans, New | Total commercial | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,290,852	1,222,320
Covered loans		0
Non-PCI Loans, New | Total commercial | Lease financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,088	1,256
Covered loans		0
Non-PCI Loans, New | Total consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,292,472	1,311,550
Covered loans		0
Non-PCI Loans, New | Total consumer | 1-4 family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	745,534	733,349
Covered loans		0
Non-PCI Loans, New | Total consumer | Home equity loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	151,483	148,855
Covered loans		0
Non-PCI Loans, New | Total consumer | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	395,455	429,346
Covered loans		0
Non-PCI Loans, New | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	124,754	114,995
Covered loans		0
Non-PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	271,749	260,072
Covered loans		27,155
Non-PCI Loans | Total commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	47,503	51,969
Covered loans		0
Non-PCI Loans | Total commercial real estate | Non-owner occupied commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	41,750	46,081
Covered loans		0
Non-PCI Loans | Total commercial real estate | Other commercial construction and land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	190	202
Covered loans		0
Non-PCI Loans | Total commercial real estate | Multifamily commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	5,563	5,686
Covered loans		0
Non-PCI Loans | Total commercial real estate | 1-4 family residential construction and land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	0	0
Covered loans		0
Non-PCI Loans | Total commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	41,405	43,182
Covered loans		0
Non-PCI Loans | Total commercial | Owner occupied commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	35,621	36,927
Covered loans		0
Non-PCI Loans | Total commercial | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	5,784	6,255
Covered loans		0
Non-PCI Loans | Total commercial | Lease financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	0	0
Covered loans		0
Non-PCI Loans | Total consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	180,755	162,652
Covered loans		27,155
Non-PCI Loans | Total consumer | 1-4 family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	32,929	32,194
Covered loans		2,265
Non-PCI Loans | Total consumer | Home equity loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	144,066	126,547
Covered loans		24,890
Non-PCI Loans | Total consumer | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	3,760	3,911
Covered loans		0
Non-PCI Loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	2,086	2,269
Covered loans		0
Purchased Credit- Impaired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,008,417	1,020,961
Covered loans		46,347
Purchased Credit- Impaired | Total commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	381,433	415,053
Covered loans		123
Purchased Credit- Impaired | Total commercial real estate | Non-owner occupied commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	280,341	302,752
Covered loans		0
Purchased Credit- Impaired | Total commercial real estate | Other commercial construction and land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	76,502	85,754
Covered loans		123
Purchased Credit- Impaired | Total commercial real estate | Multifamily commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	21,748	23,609
Covered loans		0
Purchased Credit- Impaired | Total commercial real estate | 1-4 family residential construction and land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	2,842	2,938
Covered loans		0
Purchased Credit- Impaired | Total commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	282,052	291,039
Covered loans		67
Purchased Credit- Impaired | Total commercial | Owner occupied commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	203,455	209,910
Covered loans		67
Purchased Credit- Impaired | Total commercial | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	78,597	81,129
Covered loans		0
Purchased Credit- Impaired | Total commercial | Lease financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	0	0
Covered loans		0
Purchased Credit- Impaired | Total consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	312,325	282,031
Covered loans		46,157
Purchased Credit- Impaired | Total consumer | 1-4 family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	236,608	211,361
Covered loans		38,622
Purchased Credit- Impaired | Total consumer | Home equity loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	72,961	67,449
Covered loans		7,535
Purchased Credit- Impaired | Total consumer | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	2,756	3,221
Covered loans		0
Purchased Credit- Impaired | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	$ 32,607	32,838
Covered loans		$ 0