Loans and Allowance for Loan Losses - Summary of Impaired Loans Disaggregated by Class (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	$ 23,704	$ 41,526
Recorded Investment, With an related allowance recorded	54,465	42,052
Recorded Investment, Total	78,169	83,578
Unpaid Principal Balance, With no related allowance recorded	35,195	70,970
Unpaid Principal Balance, With an related allowance recorded	57,240	44,303
Unpaid Principal Balance, Total	92,435	115,273
Related Allowance, With an related allowance recorded,Total	2,590	7,165
Related Allowance, With an related allowance recorded,Total	2,590	7,165
Average Recorded Investment, With no related allowance recorded	32,616	33,502
Average Recorded Investment, With an related allowance recorded	48,259	47,402
Average Recorded Investment, Total	80,875	80,904
Interest Income Recognized, With no related allowance recorded	80	619
Interest Income Recognized, With an related allowance recorded	140	703
Interest Income Recognized, Total	220	1,322
Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	21,133	38,412
Recorded Investment, With an related allowance recorded	50,751	42,052
Recorded Investment, Total	71,884	80,464
Unpaid Principal Balance, With no related allowance recorded	32,201	65,309
Unpaid Principal Balance, With an related allowance recorded	52,699	44,303
Unpaid Principal Balance, Total	84,900	109,612
Related Allowance, With an related allowance recorded,Total	2,323	7,165
Related Allowance, With an related allowance recorded,Total	2,323	7,165
Average Recorded Investment, With no related allowance recorded	29,773	29,801
Average Recorded Investment, With an related allowance recorded	46,402	42,783
Average Recorded Investment, Total	76,175	72,584
Interest Income Recognized, With no related allowance recorded	80	464
Interest Income Recognized, With an related allowance recorded	140	703
Interest Income Recognized, Total	220	1,167
Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	2,571	3,114
Recorded Investment, With an related allowance recorded	3,714
Recorded Investment, Total	6,285	3,114
Unpaid Principal Balance, With no related allowance recorded	2,994	5,661
Unpaid Principal Balance, With an related allowance recorded	4,541
Unpaid Principal Balance, Total	7,535	5,661
Related Allowance, With an related allowance recorded,Total	267
Related Allowance, With an related allowance recorded,Total	267
Average Recorded Investment, With no related allowance recorded	2,843	3,701
Average Recorded Investment, With an related allowance recorded	1,857	4,619
Average Recorded Investment, Total	4,700	8,320
Interest Income Recognized, With no related allowance recorded		155
Interest Income Recognized, Total		155
Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	16,746	37,426
Recorded Investment, With an related allowance recorded	41,620	35,850
Recorded Investment, Total	58,366	73,276
Unpaid Principal Balance, With no related allowance recorded	19,467	59,975
Unpaid Principal Balance, With an related allowance recorded	43,502	37,917
Unpaid Principal Balance, Total	62,969	97,892
Related Allowance, With an related allowance recorded,Total	2,174	6,377
Related Allowance, With an related allowance recorded,Total	2,174	6,377
Average Recorded Investment, With no related allowance recorded	27,087	27,048
Average Recorded Investment, With an related allowance recorded	38,735	45,851
Average Recorded Investment, Total	65,822	72,899
Interest Income Recognized, With no related allowance recorded	80	619
Interest Income Recognized, With an related allowance recorded	140	703
Interest Income Recognized, Total	220	1,322
Originated loans [Member] | Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	15,082	34,705
Recorded Investment, With an related allowance recorded	41,620	35,850
Recorded Investment, Total	56,702	70,555
Unpaid Principal Balance, With no related allowance recorded	17,774	55,101
Unpaid Principal Balance, With an related allowance recorded	43,502	37,917
Unpaid Principal Balance, Total	61,276	93,018
Related Allowance, With an related allowance recorded,Total	2,174	6,377
Related Allowance, With an related allowance recorded,Total	2,174	6,377
Average Recorded Investment, With no related allowance recorded	24,894	23,793
Average Recorded Investment, With an related allowance recorded	38,735	41,232
Average Recorded Investment, Total	63,629	65,025
Interest Income Recognized, With no related allowance recorded	80	464
Interest Income Recognized, With an related allowance recorded	140	703
Interest Income Recognized, Total	220	1,167
Originated loans [Member] | Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	1,664	2,721
Recorded Investment, Total	1,664	2,721
Unpaid Principal Balance, With no related allowance recorded	1,693	4,874
Unpaid Principal Balance, Total	1,693	4,874
Average Recorded Investment, With no related allowance recorded	2,193	3,255
Average Recorded Investment, With an related allowance recorded		4,619
Average Recorded Investment, Total	2,193	7,874
Interest Income Recognized, With no related allowance recorded		155
Interest Income Recognized, Total		155
Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	2,737
Recorded Investment, With an related allowance recorded	12,845	6,202
Recorded Investment, Total	15,582	6,202
Unpaid Principal Balance, With no related allowance recorded	4,892
Unpaid Principal Balance, With an related allowance recorded	13,738	6,386
Unpaid Principal Balance, Total	18,630	6,386
Related Allowance, With an related allowance recorded,Total	416	788
Related Allowance, With an related allowance recorded,Total	416	788
Average Recorded Investment, With no related allowance recorded	1,369
Average Recorded Investment, With an related allowance recorded	9,524	1,551
Average Recorded Investment, Total	10,893	1,551
Interest Income Recognized, With no related allowance recorded
Interest Income Recognized, With an related allowance recorded
Interest Income Recognized, Total
Acquired loans [Member] | Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	2,223
Recorded Investment, With an related allowance recorded	9,131	6,202
Recorded Investment, Total	11,354	6,202
Unpaid Principal Balance, With no related allowance recorded	4,378
Unpaid Principal Balance, With an related allowance recorded	9,197	6,386
Unpaid Principal Balance, Total	13,575	6,386
Related Allowance, With an related allowance recorded,Total	149	788
Related Allowance, With an related allowance recorded,Total	149	788
Average Recorded Investment, With no related allowance recorded	1,112
Average Recorded Investment, With an related allowance recorded	7,667	1,551
Average Recorded Investment, Total	8,779	1,551
Acquired loans [Member] | Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	514
Recorded Investment, With an related allowance recorded	3,714
Recorded Investment, Total	4,228
Unpaid Principal Balance, With no related allowance recorded	514
Unpaid Principal Balance, With an related allowance recorded	4,541
Unpaid Principal Balance, Total	5,055
Related Allowance, With an related allowance recorded,Total	267
Related Allowance, With an related allowance recorded,Total	267
Average Recorded Investment, With no related allowance recorded	257
Average Recorded Investment, With an related allowance recorded	1,857
Average Recorded Investment, Total	2,114
Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	4,221	4,100
Recorded Investment, With an related allowance recorded
Recorded Investment, Total	4,221	4,100
Unpaid Principal Balance, With no related allowance recorded	10,836	10,995
Unpaid Principal Balance, With an related allowance recorded
Unpaid Principal Balance, Total	10,836	10,995
Related Allowance, With an related allowance recorded,Total
Related Allowance, With an related allowance recorded,Total
Average Recorded Investment, With no related allowance recorded	4,160	6,454
Average Recorded Investment, With an related allowance recorded
Average Recorded Investment, Total	4,160	6,454
Interest Income Recognized, With no related allowance recorded
Interest Income Recognized, With an related allowance recorded
Interest Income Recognized, Total
Covered loans [Member] | Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	3,828	3,707
Recorded Investment, Total	3,828	3,707
Unpaid Principal Balance, With no related allowance recorded	10,049	10,208
Unpaid Principal Balance, Total	10,049	10,208
Average Recorded Investment, With no related allowance recorded	3,767	6,008
Average Recorded Investment, Total	3,767	6,008
Covered loans [Member] | Residential mortgage loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment, With no related allowance recorded	393	393
Recorded Investment, Total	393	393
Unpaid Principal Balance, With no related allowance recorded	787	787
Unpaid Principal Balance, Total	787	787
Average Recorded Investment, With no related allowance recorded	393	446
Average Recorded Investment, Total	$ 393	$ 446