Loans - Additional Information (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans net of unearned discount and deferred loan fees	$ 15,300,000				$ 3,500,000				$ 15,300,000	$ 3,500,000
Loans	17,236,103,000				16,043,107,000				17,236,103,000	16,043,107,000
Loans transferred to loans held for sale									174,501,000	0	$ 27,329,000
Gains on sales of loans, net	12,307,000	$ 4,823,000	$ 3,105,000	$ 1,795,000	1,211,000	$ 2,014,000	$ 422,000	$ 598,000	22,030,000	4,245,000	1,731,000
Sales of loans									0	0
Net (decrease) increase in expected cash flows									(9,989,000)	57,119,000
FDIC loss-share receivable	$ 7,200,000				8,300,000				7,200,000	8,300,000
Non-interest income, increase (decrease)									$ 1,300,000	3,300,000	20,800,000
Combined loan-to-value ratio home equity loan	75.00%								75.00%
Accrued interest on non-accrual loans									$ 2,100,000	3,500,000	2,200,000
Interest income recognized and classified as non-accrual									207,000	1,300,000	$ 735,000
TDRs not reported as non-accrual loans	$ 85,200,000				77,600,000				85,200,000	77,600,000
Non-performing TDRs	10,600,000				21,000,000				10,600,000	21,000,000
Specific reserves for loan losses									4,800,000	1,400,000
Troubled debt restructuring, charge-offs									$ 0	320,000
Number of days loans placed on non-accrual status									90 days
PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,771,502,000				2,240,471,000				$ 1,771,502,000	2,240,471,000
Covered loans	70,400,000				122,300,000				70,400,000	122,300,000
PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,900,000,000				2,400,000,000				1,900,000,000	2,400,000,000
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecured loans	7,000,000				7,100,000				7,000,000	7,100,000
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,867,918,000				3,130,541,000				2,867,918,000	3,130,541,000
Loans transferred to loans held for sale		$ 174,500,000
Gains on sales of loans, net	7,300,000
Residential mortgage | PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	183,723,000				218,462,000				183,723,000	218,462,000
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,638,195,000				2,540,491,000				2,638,195,000	2,540,491,000
Unsecured loans	455,500,000				386,600,000				455,500,000	386,600,000
Impaired loans	250,000								250,000
Commercial and industrial | PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	281,177,000				383,942,000				281,177,000	383,942,000
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,185,377,000				2,192,492,000				2,185,377,000	2,192,492,000
Unsecured loans	20,600,000				18,800,000				20,600,000	18,800,000
Consumer | PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 100,583,000				$ 135,710,000				$ 100,583,000	$ 135,710,000