Loans and Leases - Additional Information (Detail) - USD ($)			6 Months Ended		12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Feb. 13, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying amount	$ 14,563,128,000	$ 12,190,440,000	$ 14,563,128,000		$ 12,190,440,000
Loans acquired and accounted for under ASC 310-30, Fair value						$ 1,665,548,000
Loans acquired and accounted for under ASC 310-30, Contractual cash flows not expected to be collected						2,291,087,000
Sustained period of delinquency for impairment evaluation			90 days	90 days
Minimum reserves for commercial loan	500,000		$ 500,000
Minimum amount to allocate specific valuation allowance	500,000		500,000
Restructured loans returned to performing status			3,968,000,000
Valuation for impairment of loans with pooled reserves	500,000	500,000	500,000		500,000
Pooled reserves for all other classes of loans			3,300,000		3,500,000
Loan Purchased not Subject to ASC 310-30 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, Fair value						292,300,000
Loans acquired and accounted for under ASC 310-30, Unpaid principal balance						315,100,000
Loans acquired and accounted for under ASC 310-30, Contractual cash flows not expected to be collected						$ 103,000,000
Purchased Credit-Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying amount	7,100,000	5,900,000	7,100,000		5,900,000
Consumer Lines of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Consumer loans	187,800,000	186,200,000	187,800,000		186,200,000
Carrying amount	$ 1,290,053,000	$ 1,137,255,000	$ 1,290,053,000		$ 1,137,255,000
Loan Portfolio Diversification Risk [Member] | Loans and Leases Receivable Net of Deferred Income [Member] | Consumer Lines of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of portfolio			1.30%		1.50%
Credit Concentration Risk [Member] | Acquired Loans Receivable [Member] | Purchased Credit-Impaired Loans [Member] | Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of portfolio	1.00%	1.00%
Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Threshold period past due for default non-accrual status of trade accounts receivable			90 days
Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Threshold period past due for default non-accrual status of trade accounts receivable			120 days
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Threshold period past due for default non-accrual status of trade accounts receivable			180 days
Carrying value of OREO through foreclosure	$ 4,700,000	$ 5,200,000	$ 4,700,000		$ 5,200,000
Mortgage loans on real estate, foreclosure			$ 9,700,000		$ 11,700,000