Loans and Allowance for Credit Losses - Schedule of Activity in Allowance for Loan Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance			$ 49,047
Provision	3,693	(393)	2,848	(2,449)
Ending balance	43,890	50,424	43,890	50,424
Commercial Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	16,967	18,094	14,642	19,964
Charge-offs	(859)	(1,972)	(1,969)	(3,240)
Recoveries	1,314	849	2,029	2,293
Provision	(2,338)	879	382	(1,167)
Ending balance	15,084	17,850	15,084	17,850
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	28,446	27,818	31,289	26,993
Charge-offs	(1,065)	(718)	(2,801)	(4,093)
Recoveries	849	1,553	1,738	2,121
Provision	(1,635)	(32)	(3,631)	3,600
Ending balance	26,595	28,621	26,595	28,621
Consumer Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	4,685	5,646	5,155	6,954
Charge-offs	(1,612)	(2,125)	(3,514)	(4,550)
Recoveries	1,174	1,188	2,408	2,525
Provision	597	(27)	795	(247)
Ending balance	4,844	4,682	4,844	4,682
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	3,383	4,358	3,677	4,149
Charge-offs	(454)	(360)	(711)	(920)
Recoveries	183	36	223	115
Provision	(317)	(427)	(394)	263
Ending balance	2,795	3,607	2,795	3,607
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	53,481	55,916	54,763	58,060
Charge-offs	(3,990)	(5,175)	(8,995)	(12,803)
Recoveries	3,520	3,626	6,398	7,054
Provision	(3,693)	393	(2,848)	2,449
Ending balance	$ 49,318	$ 54,760	$ 49,318	$ 54,760