Loans and Allowance for Credit Losses - Schedule of Recorded Investment in Financing Receivables (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Ending balance: individually evaluated for impairment	$ 6,531	$ 7,492
Allowance for loan losses, Ending balance: collectively evaluated for impairment	32,640	37,280
Allowance for loan losses, Ending balance: noncovered loans acquired with deteriorated credit quality	3,135	4,275
Allowance for loan losses, Ending balance: covered loans acquired with deteriorated credit quality	5,012	5,716
Total allowance for credit losses	47,318	54,763
Loans and leases outstanding, Ending balance: individually evaluated for impairment	66,513	77,237
Loans and leases outstanding, Ending balance: collectively evaluated for impairment	4,807,523	4,788,210
Loans and leases outstanding, Ending balance: loans acquired with deteriorated credit quality	45,610	83,395
Loans and leases outstanding, Ending balance: covered loans acquired with deteriorated credit quality	152,830	247,752
Total loans	5,072,476	5,196,594	5,243,166
Commercial Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Ending balance: individually evaluated for impairment	3,959	4,702
Allowance for loan losses, Ending balance: collectively evaluated for impairment	10,359	9,900
Allowance for loan losses, Ending balance: noncovered loans acquired with deteriorated credit quality	202	40
Total allowance for credit losses	14,520	14,642
Loans and leases outstanding, Ending balance: individually evaluated for impairment	24,945	29,980
Loans and leases outstanding, Ending balance: collectively evaluated for impairment	1,376,178	1,330,913
Loans and leases outstanding, Ending balance: loans acquired with deteriorated credit quality	579	7,859
Loans and leases outstanding, Ending balance: covered loans acquired with deteriorated credit quality	14,818	23,707
Total loans	1,416,520	1,392,459
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Ending balance: individually evaluated for impairment	2,572	2,790
Allowance for loan losses, Ending balance: collectively evaluated for impairment	15,073	19,541
Allowance for loan losses, Ending balance: noncovered loans acquired with deteriorated credit quality	2,811	4,060
Allowance for loan losses, Ending balance: covered loans acquired with deteriorated credit quality	4,414	4,898
Total allowance for credit losses	24,870	31,289
Loans and leases outstanding, Ending balance: individually evaluated for impairment	41,568	47,257
Loans and leases outstanding, Ending balance: collectively evaluated for impairment	1,108,595	1,175,830
Loans and leases outstanding, Ending balance: loans acquired with deteriorated credit quality	30,613	52,981
Loans and leases outstanding, Ending balance: covered loans acquired with deteriorated credit quality	88,526	162,641
Total loans	1,269,302	1,438,709
Consumer Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Ending balance: collectively evaluated for impairment	4,158	4,202
Allowance for loan losses, Ending balance: noncovered loans acquired with deteriorated credit quality	86	135
Allowance for loan losses, Ending balance: covered loans acquired with deteriorated credit quality	567	818
Total allowance for credit losses	4,811	5,155
Loans and leases outstanding, Ending balance: collectively evaluated for impairment	978,419	946,654
Loans and leases outstanding, Ending balance: loans acquired with deteriorated credit quality	14,262	22,432
Loans and leases outstanding, Ending balance: covered loans acquired with deteriorated credit quality	19,477	35,741
Total loans	1,012,158	1,004,827
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Ending balance: collectively evaluated for impairment	3,050	3,637
Allowance for loan losses, Ending balance: noncovered loans acquired with deteriorated credit quality	36	40
Allowance for loan losses, Ending balance: covered loans acquired with deteriorated credit quality	31
Total allowance for credit losses	3,117	3,677
Loans and leases outstanding, Ending balance: collectively evaluated for impairment	1,344,331	1,334,813
Loans and leases outstanding, Ending balance: loans acquired with deteriorated credit quality	156	123
Loans and leases outstanding, Ending balance: covered loans acquired with deteriorated credit quality	30,009	25,663
Total loans	1,374,496	1,360,599
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses, Ending balance: individually evaluated for impairment
Allowance for loan losses, Ending balance: collectively evaluated for impairment
Allowance for loan losses, Ending balance: noncovered loans acquired with deteriorated credit quality
Allowance for loan losses, Ending balance: covered loans acquired with deteriorated credit quality
Total allowance for credit losses
Loans and leases outstanding, Ending balance: individually evaluated for impairment
Loans and leases outstanding, Ending balance: collectively evaluated for impairment
Loans and leases outstanding, Ending balance: loans acquired with deteriorated credit quality
Loans and leases outstanding, Ending balance: covered loans acquired with deteriorated credit quality
Total loans