Allowance for Loan Losses - Recorded Investment in Commercial Loan Classes by Internally Assigned Risk Ratings (Details) - Commercial - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans recorded investment	$ 4,672,445	$ 4,503,594
% of Total	100.00%	100.00%
Pass
Financing Receivable, Recorded Investment [Line Items]
Loans recorded investment	$ 4,403,909	$ 4,302,762
% of Total	94.30%	95.50%
Special mention
Financing Receivable, Recorded Investment [Line Items]
Loans recorded investment	$ 87,344	$ 130,101
% of Total	1.80%	2.90%
Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans recorded investment	$ 181,192	$ 70,731
% of Total	3.90%	1.60%
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans recorded investment	$ 2,921,832	$ 2,685,994
% of Total	100.00%	100.00%
Commercial real estate | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans recorded investment	$ 2,776,292	$ 2,588,847
% of Total	95.00%	96.40%
Commercial real estate | Special mention
Financing Receivable, Recorded Investment [Line Items]
Loans recorded investment	$ 54,627	$ 66,436
% of Total	1.90%	2.50%
Commercial real estate | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans recorded investment	$ 90,913	$ 30,711
% of Total	3.10%	1.10%
Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Loans recorded investment	$ 1,493,416	$ 1,433,266
% of Total	100.00%	100.00%
Commercial and industrial | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans recorded investment	$ 1,394,427	$ 1,345,810
% of Total	93.40%	93.90%
Commercial and industrial | Special mention
Financing Receivable, Recorded Investment [Line Items]
Loans recorded investment	$ 25,368	$ 54,320
% of Total	1.70%	3.80%
Commercial and industrial | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans recorded investment	$ 73,621	$ 33,136
% of Total	4.90%	2.30%
Commercial construction
Financing Receivable, Recorded Investment [Line Items]
Loans recorded investment	$ 257,197	$ 384,334
% of Total	100.00%	100.00%
Commercial construction | Pass
Financing Receivable, Recorded Investment [Line Items]
Loans recorded investment	$ 233,190	$ 368,105
% of Total	90.70%	95.80%
Commercial construction | Special mention
Financing Receivable, Recorded Investment [Line Items]
Loans recorded investment	$ 7,349	$ 9,345
% of Total	2.80%	2.40%
Commercial construction | Substandard
Financing Receivable, Recorded Investment [Line Items]
Loans recorded investment	$ 16,658	$ 6,884
% of Total	6.50%	1.80%