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	Jun. 30, 2014	Dec. 31, 2013
Allowance for Loan Losses [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	$ 15,810	$ 23,525
Collectively evaluated for impairment	86,132	83,022
Loans acquired with discounts related to credit quality	1,111	7,070
Total	103,053	113,617
Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	166,830	191,348
Collectively evaluated for impairment	10,970,993	10,569,996
Loans acquired with discounts related to credit quality	675,605	806,268
Total	11,813,428	11,567,612
Commercial and Industrial [Member] | Allowance for Loan Losses [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	5,586	11,032
Collectively evaluated for impairment	41,753	40,007
Loans acquired with discounts related to credit quality	1,082	512
Total	48,421	51,551
Commercial and Industrial [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	31,914	47,303
Collectively evaluated for impairment	1,879,076	1,772,833
Loans acquired with discounts related to credit quality	169,622	201,197
Total	2,080,612	2,021,333
Commercial Real Estate [Member] | Allowance for Loan Losses [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	6,622	8,676
Collectively evaluated for impairment	28,645	27,235
Loans acquired with discounts related to credit quality	0	6,432
Total	35,267	42,343
Commercial Real Estate [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	107,193	114,638
Collectively evaluated for impairment	4,996,978	4,814,159
Loans acquired with discounts related to credit quality	448,271	543,603
Total	5,552,442	5,472,400
Residential Mortgage [Member] | Allowance for Loan Losses [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	3,539	3,735
Collectively evaluated for impairment	3,450	3,928
Loans acquired with discounts related to credit quality	29	123
Total	7,018	7,786
Residential Mortgage [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	26,326	28,313
Collectively evaluated for impairment	2,421,648	2,456,926
Loans acquired with discounts related to credit quality	20,990	22,349
Total	2,468,964	2,507,588
Consumer [Member] | Allowance for Loan Losses [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	63	82
Collectively evaluated for impairment	5,305	4,274
Loans acquired with discounts related to credit quality	0	3
Total	5,368	4,359
Consumer [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	1,397	1,094
Collectively evaluated for impairment	1,673,291	1,526,078
Loans acquired with discounts related to credit quality	36,722	39,119
Total	1,711,410	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	6,979	7,578
Loans acquired with discounts related to credit quality	0	0
Total	6,979	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