Allowance for Loan Losses - Recorded Investment in Commercial Loan Classes by Internally Assigned Risk Ratings (Details) - Commercial - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 4,561,391	$ 4,355,395
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	$ 4,353,041	$ 4,169,721
Total percentage of recorded investment in commercial loan	95.40%	95.70%
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 120,574	$ 88,198
Total percentage of recorded investment in commercial loan	2.60%	2.00%
Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 87,776	$ 97,476
Total percentage of recorded investment in commercial loan	2.00%	2.30%
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 2,681,693	$ 2,498,476
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	$ 2,587,393	$ 2,423,742
Total percentage of recorded investment in commercial loan	96.50%	97.00%
Commercial Real Estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 55,218	$ 33,098
Total percentage of recorded investment in commercial loan	2.10%	1.30%
Commercial Real Estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 39,082	$ 41,636
Total percentage of recorded investment in commercial loan	1.40%	1.70%
Commercial and Industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 1,446,811	$ 1,401,035
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	$ 1,354,269	$ 1,315,507
Total percentage of recorded investment in commercial loan	93.60%	93.90%
Commercial and Industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 53,853	$ 40,409
Total percentage of recorded investment in commercial loan	3.70%	2.90%
Commercial and Industrial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 38,689	$ 45,119
Total percentage of recorded investment in commercial loan	2.70%	3.20%
Commercial Construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 432,887	$ 455,884
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	$ 411,379	$ 430,472
Total percentage of recorded investment in commercial loan	95.00%	94.40%
Commercial Construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 11,503	$ 14,691
Total percentage of recorded investment in commercial loan	2.70%	3.20%
Commercial Construction | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 10,005	$ 10,721
Total percentage of recorded investment in commercial loan	2.30%	2.40%