Other Comprehensive Income and Loss - Tax Effect on Each Component (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Tax effect on each component of other comprehensive loss
Pretax amount	$ 16	$ 25	$ 82	$ 22
Tax	(5)	(10)	(22)	(9)
After Tax Amount	11	15	60	13
Accumulated Other Comprehensive Loss
Tax effect on each component of other comprehensive loss
After Tax Amount	11	15	60	13
Unrealized Loss on Securities
Tax effect on each component of other comprehensive loss
Pretax amount	16	25	82	22
Tax	(5)	(10)	(22)	(9)
After Tax Amount	$ 11	$ 15	$ 60	$ 13

Amount of tax expense (benefit) allocated to other comprehensive income (loss) attributable to parent entity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=84161450&loc=SL4573702-111684

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=96868048&loc=SL4569616-111683

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=96868048&loc=SL4569643-111683

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration