Allowance for Loan Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	$ 5,708,067	$ 5,563,123
Total nonaccrual loans	45,992	42,635
Total past due	53,114	52,089
Total Loans	5,761,181	5,615,212
Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	2,605,369	2,479,513
Total nonaccrual loans	8,617	16,172
Total past due	9,355	18,963
Total Loans	2,614,724	2,498,476
Commercial And Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	1,397,625	1,391,475
Total nonaccrual loans	21,879	8,071
Total past due	24,672	9,560
Total Loans	1,422,297	1,401,035
Commercial Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	451,001	450,410
Total nonaccrual loans	3,758	4,927
Total past due	4,210	5,474
Total Loans	455,211	455,884
Residential Mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	690,524	689,635
Total nonaccrual loans	8,218	9,918
Total past due	10,086	12,347
Total Loans	700,610	701,982
Home Equity Loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	474,824	476,866
Total nonaccrual loans	3,484	3,439
Total past due	4,578	5,418
Total Loans	479,402	482,284
Installment and Other Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	70,006	65,525
Total nonaccrual loans	36	108
Total past due	213	327
Total Loans	70,219	65,852
Consumer Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	4,363	5,906
Total nonaccrual loans	0	0
Total past due	0	0
Total Loans	4,363	5,906
Loans Held for Sale
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	14,355	3,793
Total nonaccrual loans	0	0
Total past due	0	0
Total Loans	14,355	3,793
30 to 59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	6,074	6,598
30 to 59 Days Past Due | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	664	2,032
30 to 59 Days Past Due | Commercial And Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2,245	1,061
30 to 59 Days Past Due | Commercial Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	452	547
30 to 59 Days Past Due | Residential Mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,584	1,312
30 to 59 Days Past Due | Home Equity Loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,007	1,470
30 to 59 Days Past Due | Installment and Other Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	122	176
30 to 59 Days Past Due | Consumer Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
30 to 59 Days Past Due | Loans Held for Sale
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
60 to 89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,048	2,856
60 to 89 Days Past Due | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	74	759
60 to 89 Days Past Due | Commercial And Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	548	428
60 to 89 Days Past Due | Commercial Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
60 to 89 Days Past Due | Residential Mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	284	1,117
60 to 89 Days Past Due | Home Equity Loan
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	87	509
60 to 89 Days Past Due | Installment and Other Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	55	43
60 to 89 Days Past Due | Consumer Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
60 to 89 Days Past Due | Loans Held for Sale
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 0	$ 0