Net Loss per Share - Antidilutive (Details) - shares	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Restricted Stock Units
Potential dilutive securities that would have been anti-dilutive
Potential dilutive securities that would have been anti-dilutive due to net loss (in shares)	1,281,880	1,244,229
Stock options
Potential dilutive securities that would have been anti-dilutive
Potential dilutive securities that would have been anti-dilutive due to net loss (in shares)	4,334,612	4,803,073

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Name:	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration