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	Dec. 31, 2015	Dec. 31, 2014
Allowance for Loan Losses [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	$ 8,782	$ 12,525
Collectively evaluated for impairment	97,396	89,628
Total loans	106,178	102,353
Allowance for Loan Losses [Member] | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans		200
Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	132,388	145,008
Collectively evaluated for impairment	13,670,248	11,607,104
Total loans	16,043,107	13,473,913
Loans [Member] | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	2,240,471	1,721,801
Commercial and industrial [Member] | Allowance for Loan Losses [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	3,439	4,929
Collectively evaluated for impairment	45,328	38,577
Total loans	48,767	43,676
Commercial and industrial [Member] | Allowance for Loan Losses [Member] | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans		170
Commercial and industrial [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	25,714	28,224
Collectively evaluated for impairment	2,130,835	1,931,703
Total loans	2,540,491	2,251,111
Commercial and industrial [Member] | Loans [Member] | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	383,942	291,184
Commercial real estate loans [Member] | Allowance for Loan Losses [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	3,671	5,502
Collectively evaluated for impairment	44,335	37,338
Total loans	48,006	42,840
Commercial real estate loans [Member] | Allowance for Loan Losses [Member] | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans		0
Commercial real estate loans [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	81,930	91,298
Collectively evaluated for impairment	6,595,296	5,438,538
Total loans	8,179,583	6,694,015
Commercial real estate loans [Member] | Loans [Member] | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,502,357	1,164,179
Residential mortgage [Member] | Allowance for Loan Losses [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	1,377	1,629
Collectively evaluated for impairment	3,248	3,434
Total loans	4,625	5,093
Residential mortgage [Member] | Allowance for Loan Losses [Member] | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans		30
Residential mortgage [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	22,612	22,340
Collectively evaluated for impairment	2,889,467	2,396,704
Total loans	3,130,541	2,576,372
Residential mortgage [Member] | Loans [Member] | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	218,462	157,328
Consumer [Member] | Allowance for Loan Losses [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	295	465
Collectively evaluated for impairment	4,485	4,714
Total loans	4,780	5,179
Consumer [Member] | Allowance for Loan Losses [Member] | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans		0
Consumer [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	2,132	3,146
Collectively evaluated for impairment	2,054,650	1,840,159
Total loans	2,192,492	1,952,415
Consumer [Member] | Loans [Member] | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	135,710	109,110
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	0	5,565
Total loans	0	5,565
Unallocated [Member] | Allowance for Loan Losses [Member] | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans		0
Unallocated [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	0	0
Total loans	0	0
Unallocated [Member] | Loans [Member] | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	$ 0	$ 0