Condensed Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Statement Of Cash Flows [Abstract]
Underwriters' discounts and commisions and offering costs	$ 1,705	$ 1,705

The cash outflow for cost incurred directly with the issuance of an equity security.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3291-108585

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