Allowance for Loan Losses - Recorded Investment in Commercial Loan Classes by Internally Assigned Risk Ratings (Detail) - Commercial - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 3,973,643	$ 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	$ 3,774,015	$ 3,653,344
Total percentage of recorded investment in commercial loan	95.00%	95.20%
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 75,667	$ 83,680
Total percentage of recorded investment in commercial loan	1.90%	2.20%
Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 123,961	$ 99,853
Total percentage of recorded investment in commercial loan	3.10%	2.60%
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 2,260,231	$ 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	$ 2,179,599	$ 2,094,851
Total percentage of recorded investment in commercial loan	96.40%	96.70%
Commercial Real Estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 26,788	$ 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	$ 53,844	$ 51,814
Total percentage of recorded investment in commercial loan	2.40%	2.40%
Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 1,334,119	$ 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	$ 1,253,947	$ 1,182,685
Total percentage of recorded investment in commercial loan	94.00%	94.10%
Commercial and Industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 28,517	$ 43,896
Total percentage of recorded investment in commercial loan	2.10%	3.50%
Commercial and Industrial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 51,655	$ 30,249
Total percentage of recorded investment in commercial loan	3.90%	2.40%
Commercial Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 379,293	$ 413,444
Total percentage of recorded investment in commercial loan	100.00%	100.00%
Commercial Construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 340,469	$ 375,808
Total percentage of recorded investment in commercial loan	89.80%	90.90%
Commercial Construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 20,362	$ 19,846
Total percentage of recorded investment in commercial loan	5.40%	4.80%
Commercial Construction | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 18,462	$ 17,790
Total percentage of recorded investment in commercial loan	4.80%	4.30%