Loans Receivable and Related Allowance for Loan Losses - Activity in Allowance for Loan Losses by Portfolio (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Allowance for loan losses:
Beginning Balance	$ 5,935	$ 5,688	$ 6,127	$ 5,545	$ 5,545
Charge-offs	(147)	(128)	(732)	(174)
Recoveries	30	6	43	33
Provision	300	201	680	363
Ending Balance	6,118	5,767	6,118	5,767	6,127
Ending ALL balance attributable to loans:
Individually evaluated for impairment	7		7		7
Acquired loans collectively evaluated for impairment			0		0
Originated loans collectively evaluated for impairment	6,111		6,111		6,120
Total loans:
Individually evaluated for impairment	497		497		1,916
Acquired loans collectively evaluated for impairment			56,431		62,921
Originated loans collectively evaluated for impairment	536,448		536,448		518,524
Total	593,376		593,376		583,361
Residential Mortgages
Allowance for loan losses:
Beginning Balance	1,919	1,956	2,090	1,846	1,846
Charge-offs	0	(10)	(61)	(36)
Recoveries	0	0	3	0
Provision	114	48	1	184
Ending Balance	2,033	1,994	2,033	1,994	2,090
Ending ALL balance attributable to loans:
Individually evaluated for impairment	7		7		7
Acquired loans collectively evaluated for impairment			0		0
Originated loans collectively evaluated for impairment	2,026		2,026		2,083
Total loans:
Individually evaluated for impairment	408		408		425
Acquired loans collectively evaluated for impairment			18,501		20,300
Originated loans collectively evaluated for impairment	211,595		211,595		201,098
Total	230,504		230,504		221,823
Home Equity & Lines of Credit
Allowance for loan losses:
Beginning Balance	651	648	646	633	633
Charge-offs	(63)	(10)	(83)	(11)
Recoveries	10	1	11	20
Provision	52	0	76	(3)
Ending Balance	650	639	650	639	646
Ending ALL balance attributable to loans:
Individually evaluated for impairment	0		0		0
Acquired loans collectively evaluated for impairment			0		0
Originated loans collectively evaluated for impairment	650		650		646
Total loans:
Individually evaluated for impairment	7		7		8
Acquired loans collectively evaluated for impairment			10,203		10,873
Originated loans collectively evaluated for impairment	90,244		90,244		89,059
Total	100,454		100,454		99,940
Commercial Real Estate
Allowance for loan losses:
Beginning Balance	2,751	2,449	2,753	2,314	2,314
Charge-offs	(33)	(90)	(418)	(90)
Recoveries	16	2	18	4
Provision	148	99	529	232
Ending Balance	2,882	2,460	2,882	2,460	2,753
Ending ALL balance attributable to loans:
Individually evaluated for impairment	0		0		0
Acquired loans collectively evaluated for impairment			0		0
Originated loans collectively evaluated for impairment	2,882		2,882		2,753
Total loans:
Individually evaluated for impairment	43		43		914
Acquired loans collectively evaluated for impairment			24,247		27,404
Originated loans collectively evaluated for impairment	174,312		174,312		164,750
Total	198,602		198,602		193,068
Commercial Business
Allowance for loan losses:
Beginning Balance	560	583	585	700	700
Charge-offs	0	(10)	0	(10)
Recoveries	1	0	2	0
Provision	(62)	48	(88)	(69)
Ending Balance	499	621	499	621	585
Ending ALL balance attributable to loans:
Individually evaluated for impairment	0		0		0
Acquired loans collectively evaluated for impairment			0		0
Originated loans collectively evaluated for impairment	499		499		585
Total loans:
Individually evaluated for impairment	39		39		569
Acquired loans collectively evaluated for impairment			2,173		1,451
Originated loans collectively evaluated for impairment	52,481		52,481		56,921
Total	54,693		54,693		58,941
Consumer
Allowance for loan losses:
Beginning Balance	54	52	53	52	52
Charge-offs	(51)	(8)	(170)	(27)
Recoveries	3	3	9	9
Provision	48	6	162	19
Ending Balance	54	$ 53	54	$ 53	53
Ending ALL balance attributable to loans:
Individually evaluated for impairment	0		0		0
Acquired loans collectively evaluated for impairment			0		0
Originated loans collectively evaluated for impairment	54		54		53
Total loans:
Individually evaluated for impairment	0		0		0
Acquired loans collectively evaluated for impairment			1,307		2,893
Originated loans collectively evaluated for impairment	7,816		7,816		6,696
Total	$ 9,123		$ 9,123		$ 9,589

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Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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Amount of addition to allowance reserve for credit loss arising from purchase of loan and lease portfolios.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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The balance of financing receivables that were collectively evaluated for impairment.

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The amount of any significant purchases of financing receivables during the reporting period.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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Amount of expense related to estimated loss from loan and lease transactions.

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