Stockholders' Equity - Convertible Preferred Stock (Details) - shares	Dec. 31, 2017	Dec. 31, 2016
Preferred stock, shares authorized	3,000,000	3,000,000
Preferred stock, shares outstanding	0	0
Series C-1 Preferred Stock
Preferred stock, shares authorized	350,000
Preferred stock, shares outstanding	0	0

Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant