Loans and Allowance for Loan Losses (Activity in Allowance for Loan Losses by Portfolio Segment) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve for unfunded commitments	$ 20,000	$ 11,000	$ 22,000
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	23,116,000	21,166,000	21,116,000
Loans charged off	(2,468,000)	(3,805,000)	(2,616,000)
Recoveries	497,000	486,000	728,000
Provision for Loan and Lease Losses	3,026,000	5,269,000	1,938,000
Ending balance	24,171,000	23,116,000	21,166,000
Ending Balance: Individually evaluated for impairment	2,009,000	2,007,000	1,369,000
Ending Balance: Collectively evaluated for impairment	22,162,000	21,109,000	19,797,000
Ending Balance: Individually evaluated for impairment	13,590,000	20,254,000	15,235,000
Ending Balance: Collectively evaluated for impairment	2,768,849,000	2,574,310,000	2,474,971,000
Total loan balances	2,782,439,000	2,594,564,000	2,490,206,000
Residential real estate loans
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	4,160,000	4,545,000	4,899,000
Loans charged off	(482,000)	(356,000)	(801,000)
Recoveries	30,000	95,000	55,000
Provision for Loan and Lease Losses	1,378,000	(124,000)	392,000
Ending balance	5,086,000	4,160,000	4,545,000
Ending Balance: Individually evaluated for impairment	568,000	483,000	544,000
Ending Balance: Collectively evaluated for impairment	4,518,000	3,677,000	4,001,000
Ending Balance: Individually evaluated for impairment	5,171,000	4,348,000	6,026,000
Ending Balance: Collectively evaluated for impairment	853,198,000	798,146,000	814,591,000
Total loan balances	858,369,000	802,494,000	820,617,000
Commercial real estate loans
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	12,154,000	10,432,000	7,951,000
Loans charged off	(124,000)	(315,000)	(481,000)
Recoveries	141,000	50,000	74,000
Provision for Loan and Lease Losses	(308,000)	1,987,000	2,888,000
Ending balance	11,863,000	12,154,000	10,432,000
Ending Balance: Individually evaluated for impairment	1,441,000	1,373,000	644,000
Ending Balance: Collectively evaluated for impairment	10,422,000	10,781,000	9,788,000
Ending Balance: Individually evaluated for impairment	6,199,000	13,317,000	4,610,000
Ending Balance: Collectively evaluated for impairment	1,157,824,000	1,037,463,000	923,341,000
Total loan balances	1,164,023,000	1,050,780,000	927,951,000
Commercial loans
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	3,755,000	3,241,000	3,354,000
Loans charged off	(1,014,000)	(2,218,000)	(655,000)
Recoveries	301,000	332,000	389,000
Provision for Loan and Lease Losses	1,129,000	2,400,000	153,000
Ending balance	4,171,000	3,755,000	3,241,000
Ending Balance: Individually evaluated for impairment			92,000
Ending Balance: Collectively evaluated for impairment	4,171,000	3,755,000	3,149,000
Ending Balance: Individually evaluated for impairment	1,791,000	2,028,000	3,937,000
Ending Balance: Collectively evaluated for impairment	371,609,000	331,611,000	293,784,000
Total loan balances	373,400,000	333,639,000	297,721,000
Home equity loans
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	2,194,000	2,731,000	2,247,000
Loans charged off	(434,000)	(308,000)	(525,000)
Recoveries	2,000	2,000	188,000
Provision for Loan and Lease Losses	605,000	(231,000)	821,000
Ending balance	2,367,000	2,194,000	2,731,000
Ending Balance: Individually evaluated for impairment		86,000	89,000
Ending Balance: Collectively evaluated for impairment	2,367,000	2,108,000	2,642,000
Ending Balance: Individually evaluated for impairment	429,000	457,000	588,000
Ending Balance: Collectively evaluated for impairment	322,949,000	329,450,000	348,046,000
Total loan balances	323,378,000	329,907,000	348,634,000
Consumer loans
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	181,000	193,000	281,000
Loans charged off	(124,000)	(101,000)	(154,000)
Recoveries	17,000	7,000	22,000
Provision for Loan and Lease Losses	159,000	82,000	44,000
Ending balance	233,000	181,000	193,000
Ending Balance: Collectively evaluated for impairment	233,000	181,000	193,000
Ending Balance: Individually evaluated for impairment		7,000	74,000
Ending Balance: Collectively evaluated for impairment	18,149,000	17,325,000	17,879,000
Total loan balances	18,149,000	17,332,000	17,953,000
HPFC Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	672,000	24,000
Loans charged off	(290,000)	(507,000)
Recoveries	6,000
Provision for Loan and Lease Losses	63,000	1,155,000	24,000
Ending balance	451,000	672,000	24,000
Ending Balance: Individually evaluated for impairment		65,000
Ending Balance: Collectively evaluated for impairment	451,000	607,000	24,000
Ending Balance: Individually evaluated for impairment		97,000
Ending Balance: Collectively evaluated for impairment	45,120,000	60,315,000	77,330,000
Total loan balances	45,120,000	60,412,000	77,330,000
Unallocated
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	0	0	2,384,000
Provision for Loan and Lease Losses			(2,384,000)
Ending balance	$ 0	$ 0	$ 0