Loans, Leases and Allowance for Credit Losses - Additional Information (Detail) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) SecurityLoan	Jun. 30, 2016 USD ($) SecurityLoan	Dec. 31, 2016 USD ($)
Leases [Line Items]
Financing Receivable, Modifications, Number of Contracts | SecurityLoan				1
Financing Receivable, Modifications, Post-Modification Recorded Investment				$ 4,900
Financing Receivable, Modifications, Subsequent Default, Recorded Investment				395	$ 5,714
Receivable with Imputed Interest, Discount		$ (7,400)		(7,400)		$ (5,200)
Financing Receivable, Recorded Investment, Nonaccrual Status	[1]	30,071		30,071		40,272
Impaired Financing Receivable, Average Recorded Investment		107,816	$ 109,833	105,504	116,173
Aggregate carrying amount of impaired loans	[2]	8,295		8,295		10,909
Reduction in interest income due to nonaccrual loans		600	500	1,200	900
Loans And Loans Receivable Purchases		196,700	64,600	450,000	98,300
Financing Receivable, Significant Sales				9,200	23,800
Impaired loans with no allowance recorded	[3]	97,339		97,339		88,300
Impaired loans with an allowance recorded		3,878		3,878		4,239
Loans and Leases Receivable, Gain (Loss) on Sales, Net				100	2,500
Troubled Debt Restructured Loans [Member]
Leases [Line Items]
Financing Receivable, Recorded Investment, Nonaccrual Status		11,000		11,000		7,100
Impaired Financing Receivable, Average Recorded Investment		57,500	72,100	58,900	75,100
Aggregate carrying amount of impaired loans		6,900		6,900		2,500
Loan commitments outstanding						0
Impaired loans with no allowance recorded		48,300		48,300		58,300
Impaired loans with an allowance recorded		2,600		$ 2,600		600
Non-owner occupied [Member]
Leases [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment		308
Financing Receivable, Modifications, Subsequent Default, Number of Contracts | SecurityLoan				1
Aggregate carrying amount of impaired loans		0		$ 0		0
Impaired loans with no allowance recorded		21,957		21,957		25,524
Impaired loans with an allowance recorded		0		0		0
Construction and land development [Member]
Leases [Line Items]
Aggregate carrying amount of impaired loans		0		0		0
Impaired loans with no allowance recorded		12,146		12,146		14,838
Impaired loans with an allowance recorded		0		0		0
Residential real estate [Member]
Leases [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment			333
Aggregate carrying amount of impaired loans		0		0		0
Loans And Loans Receivable Purchases				102,400
Impaired loans with no allowance recorded		16,867		16,867		16,391
Impaired loans with an allowance recorded		0		0		0
Commercial and industrial [Member]
Leases [Line Items]
Aggregate carrying amount of impaired loans		7,552		7,552		7,766
Loans And Loans Receivable Purchases				347,600
Impaired loans with no allowance recorded		25,644		25,644		13,340
Impaired loans with an allowance recorded		3,135		3,135		3,301
Consumer [Member]
Leases [Line Items]
Aggregate carrying amount of impaired loans		0		0		18
Impaired loans with no allowance recorded		198		198		228
Impaired loans with an allowance recorded		0		0		1
Commercial leases [Member]
Leases [Line Items]
Aggregate carrying amount of impaired loans		0		0		0
Impaired loans with no allowance recorded		341		341		355
Impaired loans with an allowance recorded		0		0		$ 0
Commercial [Member] | Commercial and industrial [Member]
Leases [Line Items]
Impaired Financing Receivable, Average Recorded Investment		33,557	24,299	29,646	$ 28,001
Non-owner occupied [Member] | Commercial real estate [Member]
Leases [Line Items]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts | SecurityLoan					2
Impaired Financing Receivable, Average Recorded Investment		$ 22,149	$ 31,894	$ 23,274	$ 32,463

[1] Includes non-accrual TDR loans of $11.0 million and $7.1 million at June 30, 2017 and December 31, 2016, respectively.

[2] Includes TDR loans of $6.9 million and $2.5 million at June 30, 2017 and December 31, 2016, respectively.

[3] Includes TDR loans of $48.3 million and $58.3 million at June 30, 2017 and December 31, 2016, respectively.