Loans Receivable and Allowance for Credit Losses - Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning	$ 4,925	$ 3,869	$ 4,476	$ 3,602
Provisions (credits)	490	180	985	500
Loans charged-off	(141)	(8)	(190)	(75)
Recoveries	1	3	4	17
Balance, ending	5,275	4,044	5,275	4,044
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Period-end allowance allocated to loans individually evaluated for impairment	0	0	0	0
Period-end allowance allocated to loans collectively evaluated for impairment	5,275	4,044	5,275	4,044
Period-end loan balances evaluated for loans individually evaluated for impairment	14,804	16,412	14,804	16,412
Period-end loan balances evaluated for loans collectively evaluated for impairment	451,756	316,862	451,756	316,862
Total loans receivables	466,560	333,274	466,560	333,274	$ 372,483
Residential
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning	1,812	1,842	1,808	1,927
Provisions (credits)	82	(4)	85	(38)
Loans charged-off	(112)	0	(114)	(64)
Recoveries	1	3	4	16
Balance, ending	1,783	1,841	1,783	1,841
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Period-end allowance allocated to loans individually evaluated for impairment	0	0	0	0
Period-end allowance allocated to loans collectively evaluated for impairment	1,783	1,841	1,783	1,841
Period-end loan balances evaluated for loans individually evaluated for impairment	12,535	14,705	12,535	14,705
Period-end loan balances evaluated for loans collectively evaluated for impairment	176,445	177,150	176,445	177,150
Total loans receivables	188,980	191,855	188,980	191,855	192,632
Commercial and Multi-Family Real Estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning	1,598	1,322	1,441	1,015
Provisions (credits)	278	61	478	368
Loans charged-off	0	0	(43)	0
Recoveries	0	0	0	0
Balance, ending	1,876	1,383	1,876	1,383
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Period-end allowance allocated to loans individually evaluated for impairment	0	0	0	0
Period-end allowance allocated to loans collectively evaluated for impairment	1,876	1,383	1,876	1,383
Period-end loan balances evaluated for loans individually evaluated for impairment	2,090	1,232	2,090	1,232
Period-end loan balances evaluated for loans collectively evaluated for impairment	182,448	101,572	182,448	101,572
Total loans receivables	184,538	102,804	184,538	102,804	124,316
Construction
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning	315	163	248	143
Provisions (credits)	58	14	125	34
Loans charged-off	0	0	0	0
Recoveries	0	0	0	0
Balance, ending	373	177	373	177
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Period-end allowance allocated to loans individually evaluated for impairment	0	0	0	0
Period-end allowance allocated to loans collectively evaluated for impairment	373	177	373	177
Period-end loan balances evaluated for loans individually evaluated for impairment	0	0	0	0
Period-end loan balances evaluated for loans collectively evaluated for impairment	19,067	8,860	19,067	8,860
Total loans receivables	19,067	8,860	19,067	8,860	9,934
Commercial and Industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning	1,163	314	882	235
Provisions (credits)	27	222	309	301
Loans charged-off	(29)	0	(30)	0
Recoveries	0	0	0	0
Balance, ending	1,161	536	1,161	536
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Period-end allowance allocated to loans individually evaluated for impairment	0	0	0	0
Period-end allowance allocated to loans collectively evaluated for impairment	1,161	536	1,161	536
Period-end loan balances evaluated for loans individually evaluated for impairment	179	475	179	475
Period-end loan balances evaluated for loans collectively evaluated for impairment	73,137	28,822	73,137	28,822
Total loans receivables	73,316	29,297	73,316	29,297	45,155
Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning	9	15	6	9
Provisions (credits)	3	1	9	9
Loans charged-off	0	(8)	(3)	(11)
Recoveries	0	0	0	1
Balance, ending	12	8	12	8
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Period-end allowance allocated to loans individually evaluated for impairment	0	0	0	0
Period-end allowance allocated to loans collectively evaluated for impairment	12	8	12	8
Period-end loan balances evaluated for loans individually evaluated for impairment	0	0	0	0
Period-end loan balances evaluated for loans collectively evaluated for impairment	659	458	659	458
Total loans receivables	659	458	659	458	$ 446
Unallocated Financing Receivables
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance, beginning	28	213	91	273
Provisions (credits)	42	(114)	(21)	(174)
Loans charged-off	0	0	0	0
Recoveries	0	0	0	0
Balance, ending	70	99	70	99
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Period-end allowance allocated to loans individually evaluated for impairment	0	0	0	0
Period-end allowance allocated to loans collectively evaluated for impairment	70	99	70	99
Period-end loan balances evaluated for loans individually evaluated for impairment	0	0	0	0
Period-end loan balances evaluated for loans collectively evaluated for impairment	0	0	0	0
Total loans receivables	$ 0	$ 0	$ 0	$ 0

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- Definition

A valuation allowance for financing receivables that are expected to be uncollectible.

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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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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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- Definition

Amount of recovery of financing receivables doubtful of collection that were previously charged off.

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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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Amount of direct write-downs of financing receivables charged against the allowance.

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- Definition

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

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

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5074-111524

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- Definition

Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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