Loans and the Allowance for Credit Losses - Schedule of Recorded Investment in Loans by Category (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Total portfolio loans	$ 3,801,382	$ 3,687,762
Loans held for sale	14,517	21,903
Total loans	3,815,899	3,709,665
Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total portfolio loans	195,498	193,004
Commercial Real Estate - Improved Property [Member]
Financing Receivable, Recorded Investment [Line Items]
Total portfolio loans	1,685,585	1,665,341
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total portfolio loans	1,881,083	1,858,345
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total portfolio loans	542,071	478,025
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total portfolio loans	831,362	793,702
Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Total portfolio loans	280,368	277,226
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total portfolio loans	$ 266,498	$ 280,464