Age Analysis of Past Due Financing receivables (Details) $ in Thousands	Dec. 31, 2017 USD ($) loan	Dec. 31, 2016 USD ($) loan	Dec. 31, 2015 USD ($)
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	319	301
Number of Loans 60-89 Days | loan	48	72
Number of Loans 90 Days or More | loan	92	91
Number of Loans Total Past Due | loan	459	464
Principal Balance Total Past Due	$ 48,746	$ 19,911
Current	6,306,807	5,979,694
Total loans	6,355,553	5,999,605	$ 5,547,721	[1]
Recorded Investment >90 Days and Accruing	$ 8	$ 2
Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	2	8
Number of Loans 60-89 Days | loan	2	32
Number of Loans 90 Days or More | loan	14	6
Number of Loans Total Past Due | loan	18	46
Principal Balance Total Past Due	$ 32,572	$ 2,833
Current	855,956	899,220
Total loans	888,528	902,053	843,276
Recorded Investment >90 Days and Accruing	$ 0	$ 0
Commercial Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	7	5
Number of Loans 60-89 Days | loan	0	8
Number of Loans 90 Days or More | loan	9	8
Number of Loans Total Past Due | loan	16	21
Principal Balance Total Past Due	$ 4,853	$ 6,580
Current	3,111,708	3,004,218
Total loans	3,116,561	3,010,798	2,653,434
Recorded Investment >90 Days and Accruing	$ 0	$ 0
Construction Loans [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	0	0
Number of Loans 60-89 Days | loan	0	0
Number of Loans 90 Days or More | loan	0	0
Number of Loans Total Past Due | loan	0	0
Principal Balance Total Past Due	$ 0	$ 0
Current	401,797	320,391
Total loans	401,797	320,391	373,368
Recorded Investment >90 Days and Accruing	$ 0	$ 0
Small Business [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	17	9
Number of Loans 60-89 Days | loan	11	0
Number of Loans 90 Days or More | loan	10	19
Number of Loans Total Past Due | loan	38	28
Principal Balance Total Past Due	$ 540	$ 463
Current	131,830	122,263
Total loans	132,370	122,726	96,246
Recorded Investment >90 Days and Accruing	$ 0	$ 0
Residential Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	6	11
Number of Loans 60-89 Days | loan	13	9
Number of Loans 90 Days or More | loan	22	27
Number of Loans Total Past Due | loan	41	47
Principal Balance Total Past Due	$ 6,726	$ 6,734
Current	747,603	637,692
Total loans	754,329	644,426	638,606
Recorded Investment >90 Days and Accruing	$ 0	$ 0
Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	22	19
Number of Loans 60-89 Days | loan	6	11
Number of Loans 90 Days or More | loan	20	16
Number of Loans Total Past Due | loan	48	46
Principal Balance Total Past Due	$ 3,786	$ 3,093
Current	1,048,302	985,054
Total loans	1,052,088	988,147	927,803
Recorded Investment >90 Days and Accruing	$ 0	$ 0
Consumer Portfolio Segment [Member]
Age Analysis of Past Due Financing Receivables
Number of Loans 30-59 Days | loan	265	249
Number of Loans 60-89 Days | loan	16	12
Number of Loans 90 Days or More | loan	17	15
Number of Loans Total Past Due | loan	298	276
Principal Balance Total Past Due	$ 269	$ 208
Current	9,611	10,856
Total loans	9,880	11,064	$ 14,988
Recorded Investment >90 Days and Accruing	8	2
Financing Receivables, 30 to 59 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	5,971	4,519
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	195	100
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	3,060	1,518
Financing Receivables, 30 to 59 Days Past Due [Member] | Construction Loans [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	0	0
Financing Receivables, 30 to 59 Days Past Due [Member] | Small Business [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	339	323
Financing Receivables, 30 to 59 Days Past Due [Member] | Residential Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	870	1,277
Financing Receivables, 30 to 59 Days Past Due [Member] | Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	1,310	1,117
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	197	184
Financing Receivables, 60 to 89 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	3,377	4,944
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	370	253
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	0	1,957
Financing Receivables, 60 to 89 Days Past Due [Member] | Construction Loans [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	0	0
Financing Receivables, 60 to 89 Days Past Due [Member] | Small Business [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	144	0
Financing Receivables, 60 to 89 Days Past Due [Member] | Residential Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	2,385	1,950
Financing Receivables, 60 to 89 Days Past Due [Member] | Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	451	767
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	27	17
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	39,398	10,448
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial and Industrial [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	32,007	2,480
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	1,793	3,105
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Construction Loans [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Small Business [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	57	140
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Residential Real Estate [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	3,471	3,507
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Home Equity [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	2,025	1,209
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Age Analysis of Past Due Financing Receivables
Principal Balance Total Past Due	$ 45	$ 7

[1] The amount of net deferred costs on originated loans included in the ending balance was $6.1 million, $5.1 million, and $4.3 million at December 31, 2017, 2016, and 2015, respectively. Net unamortized discounts on acquired loans not deemed to be PCI included in the ending balance was $9.4 million, $8.6 million, and $6.6 million at December 31, 2017, 2016, and 2015, respectively.