Allowance for Credit Losses - Summary of Activity in Allowance for Loan Losses non-printing (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Covered loans charge-offs	$ 1,500		$ 146
Covered loans recovered	462
Loans charged-off	26,898	[1],[2]	40,249	[1]
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans charged-off	12,722	[1],[2]	19,837	[1]
Commercial real estate loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans charged-off	9,470	[1],[2]	10,846	[1]
Non-Performing Loans [Member] | Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans charged-off	4,800
Non-Performing Loans [Member] | Commercial real estate loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans charged-off	$ 4,000

[1] Includes covered loans charge-offs totaling $1.5 million and $146 thousand during 2014 and 2013, respectively, primarily in the commercial and industrial loan portfolio.

[2] The commercial and industrial loan and commercial real estate loan categories included $4.8 million and $4.0 million of charge-offs, respectively, related to the valuation of non-performing loans transferred to loans held for sale during 2014.