Loans and Allowance for Credit Losses - Schedule of Activity in Allowance for Loan Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance			$ 49,047
Provision	(1,724)	400	(4,572)	2,849
Ending balance	42,306	50,428	42,306	50,428
Commercial Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	15,084	17,850	14,642	19,964
Charge-offs	(750)	(2,485)	(2,719)	(5,725)
Recoveries	472	1,647	2,501	3,940
Provision	(286)	954	96	(213)
Ending balance	14,520	17,966	14,520	17,966
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	26,595	28,621	31,289	26,993
Charge-offs	(432)	(771)	(3,233)	(4,864)
Recoveries	1,571	2,300	3,309	4,421
Provision	(2,864)	(945)	(6,495)	2,655
Ending balance	24,870	29,205	24,870	29,205
Consumer Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	4,844	4,682	5,155	6,954
Charge-offs	(1,822)	(1,385)	(5,336)	(5,935)
Recoveries	1,132	565	3,540	3,090
Provision	657	663	1,452	416
Ending balance	4,811	4,525	4,811	4,525
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	2,795	3,607	3,677	4,149
Charge-offs	(501)	(545)	(1,212)	(1,465)
Recoveries	54	276	277	391
Provision	769	(272)	375	(9)
Ending balance	3,117	3,066	3,117	3,066
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance
Charge-offs
Recoveries
Provision
Ending balance
Loans and Leases Receivable Allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	49,318	54,760	54,763	58,060
Charge-offs	(3,505)	(5,186)	(12,500)	(17,989)
Recoveries	3,229	4,788	9,627	11,842
Provision	(1,724)	400	(4,572)	2,849
Ending balance	$ 47,318	$ 54,762	$ 47,318	$ 54,762