Loans - Additional Information (Detail) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2014	Jun. 30, 2013	Dec. 31, 2014 Contract	Dec. 31, 2013 Contract	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans net of unearned discount and deferred loan fees			$ 9,000,000	$ 5,600,000
Non-covered loans			13,262,022,000	11,471,447,000
Nonperforming loans	35,600,000
Loan charge-offs	8,300,000
Sales of loans			0	0
Non-interest income, increase (decrease)			(20,800,000)	(8,400,000)	(7,500,000)
Average expected life of the non-covered PCI loans		2 years 2 months 12 days
Previous average expected life of the non-covered PCI loans		4 years
Other Adjustments To Fdic Loss Share Receivable			(3,086,000)	0
Combined loan-to-value ratio home equity loan			75.00%
Accrued interest on non-accrual loans			2,200,000	4,800,000	7,200,000
Interest income recognized and classified as non-accrual			735,000	1,300,000	590,000
TDRs not reported as non-accrual loans			97,700,000	107,000,000
Non-performing TDRs			19,400,000	48,400,000
Specific reserves for loan losses			3,600,000	7,900,000
Number of loans modified			42	82
Number of days loans placed on non-accrual status			90 days
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructuring, charge-offs			861,000	1,100,000
Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans modified				2
Troubled debt restructuring, charge-offs			0	6,100,000
Number of borrowers whose loans were modified				1
PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans			1,600,000,000	796,100,000
Outstanding contractual principal balances			253,700,000	227,200,000
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecured loans			345,100,000	314,600,000
Commercial and Industrial [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired loans			250,000
Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans			1,946,896,000	1,565,492,000
Unsecured loans			31,400,000	21,400,000
Credit Card [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecured loans			7,600,000	8,300,000
Covered by FDIC Loss Share [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-interest income, increase (decrease)			$ 60,100,000	$ 120,900,000