Allowance for Loan Losses - Recorded Investment in Commercial Loan Classes by Internally Assigned Risk Ratings (Detail) - Commercial - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 4,173,585	$ 3,836,877
Total percentage of recorded investment in commercial loan	100.00%	100.00%
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 3,975,265	$ 3,653,344
Total percentage of recorded investment in commercial loan	95.20%	95.20%
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 81,464	$ 83,680
Total percentage of recorded investment in commercial loan	2.00%	2.20%
Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 116,856	$ 99,853
Total percentage of recorded investment in commercial loan	2.80%	2.60%
Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 1,344,297	$ 1,256,830
Total percentage of recorded investment in commercial loan	100.00%	100.00%
Commercial and Industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 1,253,411	$ 1,182,685
Total percentage of recorded investment in commercial loan	93.20%	94.10%
Commercial and Industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 37,079	$ 43,896
Total percentage of recorded investment in commercial loan	2.80%	3.50%
Commercial and Industrial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 53,807	$ 30,249
Total percentage of recorded investment in commercial loan	4.00%	2.40%
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 2,427,164	$ 2,166,603
Total percentage of recorded investment in commercial loan	100.00%	100.00%
Commercial Real Estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 2,346,848	$ 2,094,851
Total percentage of recorded investment in commercial loan	96.70%	96.70%
Commercial Real Estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 30,050	$ 19,938
Total percentage of recorded investment in commercial loan	1.20%	0.90%
Commercial Real Estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 50,266	$ 51,814
Total percentage of recorded investment in commercial loan	2.10%	2.40%
Commercial Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 402,124	$ 413,444
Total percentage of recorded investment in commercial loan	99.99%	100.00%
Commercial Construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 375,006	$ 375,808
Total percentage of recorded investment in commercial loan	93.20%	90.90%
Commercial Construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 14,335	$ 19,846
Total percentage of recorded investment in commercial loan	3.60%	4.80%
Commercial Construction | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 12,783	$ 17,790
Total percentage of recorded investment in commercial loan	3.20%	4.30%