Allowance for Loan Losses - Recorded Investment in Commercial Loan Classes by Internally Assigned Risk Ratings (Details) - Commercial - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases receivables, recorded investment	$ 4,863,864	$ 4,672,445
Total percentage of recorded investment in commercial loan	100.00%	100.00%
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases receivables, recorded investment	$ 4,618,155	$ 4,403,909
Total percentage of recorded investment in commercial loan	94.90%	94.30%
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases receivables, recorded investment	$ 110,690	$ 87,344
Total percentage of recorded investment in commercial loan	2.30%	1.80%
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases receivables, recorded investment	$ 135,019	$ 181,192
Total percentage of recorded investment in commercial loan	2.80%	3.90%
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases receivables, recorded investment	$ 2,922,197	$ 2,921,832
Total percentage of recorded investment in commercial loan	100.00%	100.00%
Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases receivables, recorded investment	$ 2,767,646	$ 2,776,292
Total percentage of recorded investment in commercial loan	94.70%	95.00%
Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases receivables, recorded investment	$ 60,096	$ 54,627
Total percentage of recorded investment in commercial loan	2.10%	1.90%
Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases receivables, recorded investment	$ 94,455	$ 90,913
Total percentage of recorded investment in commercial loan	3.20%	3.10%
Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases receivables, recorded investment	$ 1,626,854	$ 1,493,416
Total percentage of recorded investment in commercial loan	100.00%	100.00%
Commercial and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases receivables, recorded investment	$ 1,547,375	$ 1,394,427
Total percentage of recorded investment in commercial loan	95.00%	93.40%
Commercial and industrial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases receivables, recorded investment	$ 43,482	$ 25,368
Total percentage of recorded investment in commercial loan	2.70%	1.70%
Commercial and industrial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases receivables, recorded investment	$ 36,997	$ 73,621
Total percentage of recorded investment in commercial loan	2.30%	4.90%
Commercial construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases receivables, recorded investment	$ 314,813	$ 257,197
Total percentage of recorded investment in commercial loan	100.00%	100.00%
Commercial construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases receivables, recorded investment	$ 304,135	$ 233,190
Total percentage of recorded investment in commercial loan	96.60%	90.70%
Commercial construction | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases receivables, recorded investment	$ 7,112	$ 7,349
Total percentage of recorded investment in commercial loan	2.30%	2.80%
Commercial construction | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases receivables, recorded investment	$ 3,566	$ 16,658
Total percentage of recorded investment in commercial loan	1.10%	6.50%