Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits
Unrecognized tax benefit, beginning balance	$ 276	$ 276	$ 276
Additions for tax positions related to the current year	995	0	0
Unrecognized tax benefit, ending balance	$ 1,271	$ 276	$ 276

Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319

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