Allowance for Loan Losses - Recorded Investment in Commercial Loan Classes by Internally Assigned Risk Ratings (Details) - Commercial - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 4,660,290	$ 4,672,445
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	$ 4,406,993	$ 4,403,909
Total percentage of recorded investment in commercial loan	94.60%	94.30%
Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 88,037	$ 87,344
Total percentage of recorded investment in commercial loan	1.90%	1.80%
Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 165,260	$ 181,192
Total percentage of recorded investment in commercial loan	3.50%	3.90%
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 2,901,625	$ 2,921,832
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	$ 2,745,156	$ 2,776,292
Total percentage of recorded investment in commercial loan	94.60%	95.00%
Commercial real estate | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 56,829	$ 54,627
Total percentage of recorded investment in commercial loan	2.00%	1.90%
Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 99,640	$ 90,913
Total percentage of recorded investment in commercial loan	3.40%	3.10%
Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 1,513,007	$ 1,493,416
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	$ 1,427,120	$ 1,394,427
Total percentage of recorded investment in commercial loan	94.30%	93.40%
Commercial and industrial | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 23,945	$ 25,368
Total percentage of recorded investment in commercial loan	1.60%	1.70%
Commercial and industrial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 61,942	$ 73,621
Total percentage of recorded investment in commercial loan	4.10%	4.90%
Commercial construction
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 245,658	$ 257,197
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	$ 234,717	$ 233,190
Total percentage of recorded investment in commercial loan	95.50%	90.70%
Commercial construction | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 7,263	$ 7,349
Total percentage of recorded investment in commercial loan	3.00%	2.80%
Commercial construction | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivables, recorded investment	$ 3,678	$ 16,658
Total percentage of recorded investment in commercial loan	1.50%	6.50%