Loans and Allowance for Loan Losses (Loan Aging Analysis by Portfolio Segment (Including Loans Past Due Over Ninety Days and Non Accrual Loans) and Summary of Non Accrual Loans) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 22,945	$ 25,465
Current	2,759,494	2,569,099
Total loan balances	2,782,439	2,594,564	$ 2,490,206
Non-Accrual Loans	15,314	20,713
Residential real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	9,477	5,611
Current	848,892	796,883
Total loan balances	858,369	802,494	820,617
Non-Accrual Loans	4,979	3,945
Commercial real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,700	13,703
Current	1,157,323	1,037,077
Total loan balances	1,164,023	1,050,780	927,951
Non-Accrual Loans	5,642	12,849
Commercial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,223	2,526
Current	371,177	331,113
Total loan balances	373,400	333,639	297,721
Non-Accrual Loans	2,000	2,088
Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,548	2,347
Current	320,830	327,560
Total loan balances	323,378	329,907	348,634
Non-Accrual Loans	1,650	1,620
Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	67	42
Current	18,082	17,290
Total loan balances	18,149	17,332	17,953
Non-Accrual Loans		4
HPFC Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,930	1,236
Current	43,190	59,176
Total loan balances	45,120	60,412	$ 77,330
Non-Accrual Loans	1,043	207
Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,291	4,639
Financing Receivables, 30 to 59 Days Past Due [Member] | Residential real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,871	1,783
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	849	855
Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	329	633
Financing Receivables, 30 to 59 Days Past Due [Member] | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,046	892
Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	57	38
Financing Receivables, 30 to 59 Days Past Due [Member] | HPFC Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	139	438
Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,822	2,187
Financing Receivables, 60 to 89 Days Past Due [Member] | Residential real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,585	924
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	323	223
Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	359	218
Financing Receivables, 60 to 89 Days Past Due [Member] | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	173	134
Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10
Financing Receivables, 60 to 89 Days Past Due [Member] | HPFC Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,372	688
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	12,832	18,639
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Residential real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,021	2,904
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,528	12,625
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,535	1,675
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Home equity loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,329	1,321
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		4
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | HPFC Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 419	$ 110