Net Loss per Common Share - Basic and diluted (Details) - shares shares in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Computations of diluted net loss per share
Antidilutive securities excluded from calculation	6,089	5,196	6,089	5,196
Employee Stock Option
Computations of diluted net loss per share
Antidilutive securities excluded from calculation	2,452	2,541	2,452	2,541
Other unvested equity awards
Computations of diluted net loss per share
Antidilutive securities excluded from calculation	3,637	2,655	3,637	2,655

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