Loans and Allowance for Loan Losses - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	May. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Carrying amount of loans	$ 7,090,000
Non- Accrual Loans	49,955,000			$ 27,382,000
Loans modified as troubled debt restructurings	35,300,000			9,300,000
Total Past Due	77,770,000			43,169,000
Proceeds from sales of loans held for sale	79,673,000	$ 51,880,000
Commitments to lend to borrowers with loan modifications classified as TDR's	217,000
Default payment of troubled restructuring, commercial real estate loan	178,000
Greater than 90 days Past Due and Accruing [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Past Due	2,552,000			$ 3,830,000
PCI loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans modified as troubled debt restructurings	0
PCI loans [Member] | Greater than 90 days Past Due and Accruing [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Past Due	4,817,000
Loans Accounted for under ASC 310-30 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Carrying amount of loans	7,100,000
Outstanding balance of loans	8,400,000
Marquette [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans purchased at fair value			$ 980,400,000
Marquette [Member] | Non-PCI loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans purchased at fair value			972,600,000
Contractually required principal and interest at acquisition	983,900,000
Marquette [Member] | PCI loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans purchased at fair value			7,800,000
Contractually required principal and interest at acquisition	9,300,000
Marquette [Member] | Loans Accounted for under ASC 310-30 [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans purchased at fair value			7,811,000
Contractually required principal and interest at acquisition			$ 9,282,000
Carrying amount of loans	7,090,000
Outstanding balance of loans	$ 8,411,000
Revolving Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of days past due to consider loan as a loss and charged off	90 days
Closed-End Retail Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of days past due to consider loan as a loss and charged off	120 days
Open-End Retail Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of days past due to consider loan as a loss and charged off	180 days