Loans and Allowance for Loan Losses - Summary of Impaired Loans Disaggregated by Class (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	$ 92,023	$ 62,300
Unpaid Principal Balance	135,902	88,585
Related Allowance	8,602	7,567
Average Recorded Investment	75,584	86,178
Interest Income Recognized	741	678
With no related allowance recorded [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	43,514	29,633
Unpaid Principal Balance	71,970	49,494
Average Recorded Investment	20,524	21,395
Interest Income Recognized	422	417
With an allowance recorded [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	48,509	32,667
Unpaid Principal Balance	63,932	39,091
Related Allowance	8,602	7,567
Average Recorded Investment	55,060	64,783
Interest Income Recognized	319	261
Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	85,861	43,454
Unpaid Principal Balance	122,033	65,420
Related Allowance	8,602	7,539
Average Recorded Investment	65,444	52,045
Interest Income Recognized	741	678
Originated loans [Member] | With no related allowance recorded [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	43,514	11,330
Unpaid Principal Balance	71,970	26,892
Average Recorded Investment	20,524	15,079
Interest Income Recognized	422	417
Originated loans [Member] | With an allowance recorded [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	42,347	32,124
Unpaid Principal Balance	50,063	38,528
Related Allowance	8,602	7,539
Average Recorded Investment	44,920	36,966
Interest Income Recognized	319	261
Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	6,162	18,846
Unpaid Principal Balance	13,869	23,165
Related Allowance		28
Average Recorded Investment	10,140	34,133
Covered loans [Member] | With no related allowance recorded [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment		18,303
Unpaid Principal Balance		22,602
Average Recorded Investment		6,316
Covered loans [Member] | With an allowance recorded [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	6,162	543
Unpaid Principal Balance	13,869	563
Related Allowance		28
Average Recorded Investment	10,140	27,817
Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	84,106	56,420
Unpaid Principal Balance	123,043	80,195
Related Allowance	8,469	6,997
Average Recorded Investment	66,573	78,185
Interest Income Recognized	592	613
Commercial loans [Member] | With no related allowance recorded [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	36,994	28,051
Unpaid Principal Balance	61,108	46,692
Average Recorded Investment	17,661	18,461
Interest Income Recognized	273	359
Commercial loans [Member] | With an allowance recorded [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	47,112	28,369
Unpaid Principal Balance	61,935	33,503
Related Allowance	8,469	6,997
Average Recorded Investment	48,912	59,724
Interest Income Recognized	319	254
Commercial loans [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	78,337	38,211
Unpaid Principal Balance	109,961	58,103
Related Allowance	8,469	6,988
Average Recorded Investment	56,939	45,951
Interest Income Recognized	592	613
Commercial loans [Member] | Originated loans [Member] | With no related allowance recorded [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	36,994	10,177
Unpaid Principal Balance	61,108	24,935
Average Recorded Investment	17,661	13,992
Interest Income Recognized	273	359
Commercial loans [Member] | Originated loans [Member] | With an allowance recorded [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	41,343	28,034
Unpaid Principal Balance	48,853	33,168
Related Allowance	8,469	6,988
Average Recorded Investment	39,278	31,959
Interest Income Recognized	319	254
Commercial loans [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	5,769	18,209
Unpaid Principal Balance	13,082	22,092
Related Allowance		9
Average Recorded Investment	9,634	32,234
Commercial loans [Member] | Covered loans [Member] | With no related allowance recorded [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment		17,874
Unpaid Principal Balance		21,757
Average Recorded Investment		4,469
Commercial loans [Member] | Covered loans [Member] | With an allowance recorded [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	5,769	335
Unpaid Principal Balance	13,082	335
Related Allowance		9
Average Recorded Investment	9,634	27,765
Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	7,917	5,880
Unpaid Principal Balance	12,859	8,390
Related Allowance	133	570
Average Recorded Investment	9,011	7,993
Interest Income Recognized	149	65
Residential mortgage loans [Member] | With no related allowance recorded [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	6,520	1,582
Unpaid Principal Balance	10,862	2,802
Average Recorded Investment	2,863	2,934
Interest Income Recognized	149	58
Residential mortgage loans [Member] | With an allowance recorded [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	1,397	4,298
Unpaid Principal Balance	1,997	5,588
Related Allowance	133	570
Average Recorded Investment	6,148	5,059
Interest Income Recognized		7
Residential mortgage loans [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	7,524	5,243
Unpaid Principal Balance	12,072	7,317
Related Allowance	133	551
Average Recorded Investment	8,505	6,094
Interest Income Recognized	149	65
Residential mortgage loans [Member] | Originated loans [Member] | With no related allowance recorded [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	6,520	1,153
Unpaid Principal Balance	10,862	1,957
Average Recorded Investment	2,863	1,087
Interest Income Recognized	149	58
Residential mortgage loans [Member] | Originated loans [Member] | With an allowance recorded [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	1,004	4,090
Unpaid Principal Balance	1,210	5,360
Related Allowance	133	551
Average Recorded Investment	5,642	5,007
Interest Income Recognized		7
Residential mortgage loans [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	393	637
Unpaid Principal Balance	787	1,073
Related Allowance		19
Average Recorded Investment	506	1,899
Residential mortgage loans [Member] | Covered loans [Member] | With no related allowance recorded [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment		429
Unpaid Principal Balance		845
Average Recorded Investment		1,847
Residential mortgage loans [Member] | Covered loans [Member] | With an allowance recorded [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	393	208
Unpaid Principal Balance	787	228
Related Allowance		19
Average Recorded Investment	$ 506	$ 52