Loans and the Allowance for Loan Losses (Details) - Aging analysis - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	$ 53,015	$ 65,613
Total Past Due and Nonaccrual	58,626	72,784
Current	4,407,148	4,102,026
Gross Loans	4,465,774	4,174,810
Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	29,562	47,363
Total Past Due and Nonaccrual	31,689	50,918
Current	901,480	773,164
Gross Loans	933,169	824,082
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	15,927	12,757
Total Past Due and Nonaccrual	19,117	14,777
Current	2,720,826	2,578,132
Gross Loans	2,739,943	2,592,909
Commercial Construction Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	2,934
Total Past Due and Nonaccrual	2,934
Current	491,272	483,216
Gross Loans	494,206	483,216
Residential Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual	4,592	5,493
Total Past Due and Nonaccrual	4,598	7,071
Current	291,350	264,724
Gross Loans	295,948	271,795
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Nonaccrual
Total Past Due and Nonaccrual	288	18
Current	2,220	2,790
Gross Loans	2,508	2,808
30 - 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Nonaccrual	527	3,849
30 - 59 Days Past Due [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Nonaccrual	233	1,708
30 - 59 Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Nonaccrual		545
30 - 59 Days Past Due [Member] | Commercial Construction Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Nonaccrual
30 - 59 Days Past Due [Member] | Residential Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Nonaccrual	6	1,578
30 - 59 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Nonaccrual	288	18
60 - 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Nonaccrual	3,436	1,658
60 - 89 Days Past Due [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Nonaccrual	246	183
60 - 89 Days Past Due [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Nonaccrual	3,190	1,475
60 - 89 Days Past Due [Member] | Commercial Construction Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Nonaccrual
60 - 89 Days Past Due [Member] | Residential Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Nonaccrual
60 - 89 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Nonaccrual
90 Days or Greater Past Due and Still Accruing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Nonaccrual	1,648	1,664
90 Days or Greater Past Due and Still Accruing [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Nonaccrual	1,648	1,664
90 Days or Greater Past Due and Still Accruing [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Nonaccrual
90 Days or Greater Past Due and Still Accruing [Member] | Commercial Construction Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Nonaccrual
90 Days or Greater Past Due and Still Accruing [Member] | Residential Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Nonaccrual
90 Days or Greater Past Due and Still Accruing [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Nonaccrual