Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

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Loans and Allowance for Loan Losses - Schedule of Composition of Loan (Detail) (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	$ 11,292,659		$ 11,118,121	$ 9,398,124
Allowance for loan losses	(52,713)	$ (53,660)	(50,381)	(50,169)	$ (50,986)	$ (49,808)
Net loans	11,239,946		11,067,740	9,347,955
Commercial Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	2,949,277		2,717,269
Allowance for loan losses	(19,719)	$ (21,387)	(19,246)	$ (20,527)	$ (20,365)	$ (21,481)
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	2,166,203		2,167,053
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	4,481,554		4,354,552
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	1,695,625		1,879,247
Consumer [Member] \| Consumer Credit - Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	498,325		507,507
Construction [Member] \| Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	542,228		374,306
Other [Member] \| Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	3,939,326		3,980,246
Other [Member] \| Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	138,323		223,068
Consumer Credit - Auto [Member] \| Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans by lending classification	$ 1,058,977		$ 1,148,672