Allowance for Credit Losses - Summary of Allocation of Allowance for Loan Losses and Related Loans by Loan Portfolio Segment Disaggregated Based on Impairment Methodology (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Allowance for Loan Losses [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	$ 17,082	$ 23,525
Collectively evaluated for impairment	82,557	83,022
Loans acquired with discounts related to credit quality	7,070	7,070
Total	106,709	113,617
Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	166,988	191,348
Collectively evaluated for impairment	10,785,007	10,569,996
Loans acquired with discounts related to credit quality	742,599	806,268
Total	11,694,594	11,567,612
Commercial and Industrial [Member] | Allowance for Loan Losses [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	6,319	11,032
Collectively evaluated for impairment	43,101	40,007
Loans acquired with discounts related to credit quality	512	512
Total	49,932	51,551
Commercial and Industrial [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	36,123	47,303
Collectively evaluated for impairment	1,817,815	1,772,833
Loans acquired with discounts related to credit quality	186,000	201,197
Total	2,039,938	2,021,333
Commercial Real Estate [Member] | Allowance for Loan Losses [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	7,153	8,676
Collectively evaluated for impairment	24,797	27,235
Loans acquired with discounts related to credit quality	6,432	6,432
Total	38,382	42,343
Commercial Real Estate [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	102,916	114,638
Collectively evaluated for impairment	4,950,003	4,814,159
Loans acquired with discounts related to credit quality	496,816	543,603
Total	5,549,735	5,472,400
Residential Mortgage [Member] | Allowance for Loan Losses [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	3,512	3,735
Collectively evaluated for impairment	3,344	3,928
Loans acquired with discounts related to credit quality	123	123
Total	6,979	7,786
Residential Mortgage [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	26,628	28,313
Collectively evaluated for impairment	2,431,049	2,456,926
Loans acquired with discounts related to credit quality	21,439	22,349
Total	2,479,116	2,507,588
Consumer [Member] | Allowance for Loan Losses [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	98	82
Collectively evaluated for impairment	4,006	4,274
Loans acquired with discounts related to credit quality	3	3
Total	4,107	4,359
Consumer [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	1,321	1,094
Collectively evaluated for impairment	1,586,140	1,526,078
Loans acquired with discounts related to credit quality	38,344	39,119
Total	1,625,805	1,566,291
Unallocated [Member] | Allowance for Loan Losses [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	7,309	7,578
Loans acquired with discounts related to credit quality	0	0
Total	7,309	7,578
Unallocated [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	0	0
Loans acquired with discounts related to credit quality	0	0
Total	$ 0	$ 0