Loans Receivable and Related Allowance for Loan Losses - Activity in Allowance for Loan Losses by Portfolio (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at the beginning of the year	$ 5,545	$ 5,205
Charge-offs	(366)	(296)
Recoveries	45	172
Provision	903	464
Balance at the end of the year	6,127	5,545
Ending ALL balance attributable to loans:
Individually evaluated for impairment	7	120
Acquired loans	0	0
Collectively evaluated for impairment	6,120	5,425
Total loans:
Individually evaluated for impairment	1,916	1,833
Acquired loans	62,921	58,936
Collectively evaluated for impairment	518,524	460,211
Total loans, gross	583,361	520,980
Residential Mortgages
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at the beginning of the year	1,846	1,429
Charge-offs	(40)	(101)
Recoveries	0	0
Provision	284	518
Balance at the end of the year	2,090	1,846
Ending ALL balance attributable to loans:
Individually evaluated for impairment	7	19
Acquired loans	0	0
Collectively evaluated for impairment	2,083	1,827
Total loans:
Individually evaluated for impairment	425	135
Acquired loans	20,300	25,024
Collectively evaluated for impairment	201,098	173,008
Total loans, gross	221,823	198,167
Home Equity & Lines of Credit
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at the beginning of the year	633	586
Charge-offs	(114)	(118)
Recoveries	23	3
Provision	104	162
Balance at the end of the year	646	633
Ending ALL balance attributable to loans:
Individually evaluated for impairment	0	0
Acquired loans	0	0
Collectively evaluated for impairment	646	633
Total loans:
Individually evaluated for impairment	8	0
Acquired loans	10,873	5,225
Collectively evaluated for impairment	89,059	86,134
Total loans, gross	99,940	91,359
Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at the beginning of the year	2,314	2,185
Charge-offs	(127)	(18)
Recoveries	8	158
Provision	558	(11)
Balance at the end of the year	2,753	2,314
Ending ALL balance attributable to loans:
Individually evaluated for impairment	0	95
Acquired loans	0	0
Collectively evaluated for impairment	2,753	2,219
Total loans:
Individually evaluated for impairment	914	1,014
Acquired loans	27,404	27,492
Collectively evaluated for impairment	164,750	138,488
Total loans, gross	193,068	166,994
Commercial Business
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at the beginning of the year	700	960
Charge-offs	(14)	(11)
Recoveries	2	0
Provision	(103)	(249)
Balance at the end of the year	585	700
Ending ALL balance attributable to loans:
Individually evaluated for impairment	0	6
Acquired loans	0	0
Collectively evaluated for impairment	585	694
Total loans:
Individually evaluated for impairment	569	684
Acquired loans	1,451	1,182
Collectively evaluated for impairment	56,921	55,922
Total loans, gross	58,941	57,788
Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at the beginning of the year	52	45
Charge-offs	(71)	(48)
Recoveries	12	11
Provision	60	44
Balance at the end of the year	53	52
Ending ALL balance attributable to loans:
Individually evaluated for impairment	0	0
Acquired loans	0	0
Collectively evaluated for impairment	53	52
Total loans:
Individually evaluated for impairment	0	0
Acquired loans	2,893	13
Collectively evaluated for impairment	6,696	6,659
Total loans, gross	$ 9,589	$ 6,672