Loans and Allowance for Credit Losses - Schedule of Composition of Loans (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	$ 5,538,868	$ 5,082,964	$ 5,176,222
Allowance for loan losses	(42,494)	(41,741)
Allowance for loan losses - covered loans	(3,658)	(5,404)
Net loans	5,492,716	5,035,819	5,126,904
Commercial Loan Including Finance Lease [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	1,498,833	1,373,415
Commercial Real Estate - Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	135,139	88,630
Commercial Real Estate - Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	1,219,561	1,072,260
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	1,425,179	1,359,569
Consumer Credit - Heloc [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	281,823	251,102
Consumer Credit - Auto [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	696,009	620,473
Consumer Credit - Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	111,176	99,683
Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	$ 171,148	$ 217,832