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Loans and Loans Held for Sale - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($) contract	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) contract	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income	$ 4,500,000		$ 4,500,000		$ 3,200,000
Loans, net of discount related to purchase accounting adjustments	9,000,000		9,000,000		$ 10,900,000
Maximum concentration of commercial real estate and commercial construction portfolio in loans (in excess of)					7.00%
Decrease in loans held for sale during the period			23,300,000
Gain on sale of credit card portfolio	0	$ 0	2,066,000	$ 0
Commitment to lend additional funds on troubled debt restructuring	$ 700,000.0		$ 700,000.0
Minimum period of loan payment defaults following restructure for TDRs to be in default			90 days
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans modified not considered to be troubled debt restructuring | contract	1		3
Loans modified not considered to be troubled debt restructuring	$ 6,500,000		$ 8,700,000
Installment and Other Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Decrease in loans held for sale during the period			22,900,000
Gain on sale of credit card portfolio			$ 2,100,000
Commercial Real Estate and Commercial Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Out of market exposure of combined portfolio (percent)	5.30%		5.30%		5.80%
Percentage of total loans out-of-state excluding contiguous states	2.70%		2.70%		3.00%
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans modified not considered to be troubled debt restructuring | contract	1		1
Loans modified not considered to be troubled debt restructuring	$ 500,000		$ 500,000
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of commercial loans in total portfolio loans	77.00%		77.00%		76.00%
Commercial Loans	$ 4,172,654,000		$ 4,172,654,000		$ 3,836,877,000
Concentration Risk, Product			0	0
Maximum concentration of commercial real estate and commercial construction portfolio in loans (in excess of)	7.00%		7.00%		7.00%
Commercial | Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	$ 1,385,746,000		$ 1,385,746,000		$ 1,256,830,000
Commercial | Commercial Real Estate and Commercial Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	$ 2,800,000,000		$ 2,800,000,000
Combined percentage of commercial real estate and commercial construction in total commercial loans	67.00%		67.00%		67.00%
Combined percentage of commercial real estate and commercial construction in total portfolio loans	52.00%		52.00%		51.00%
Commercial | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial Loans	$ 2,388,786,000		$ 2,388,786,000		$ 2,166,603,000

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Maximum concentration of commercial real estate and commercial construction portfolio in loans.

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Net loans out of state percentage excluding contiguous states.

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