Accounting Policies - Common Stock Equivalents Excluded From Computation of Net Loss Per Share (Details) - shares shares in Thousands	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Share-based Payment Arrangement, Option
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded (in shares)	13,545	12,514
Warrant
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded (in shares)	640	640
Convertible Debt Securities
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Shares excluded (in shares)	8,729	8,224

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://fasb.org/us-gaap/role/ref/legacyRef
-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