Fair Value Measurements (Embedded and Earnout Derivative) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Fair Value Measurements
Beginning Balance	$ (5,856)	$ (6,402)	$ (6,402)
Gain (loss) on earnout derivative	31	$ (270)	546
Ending Balance	$ (5,825)		$ (5,856)

Fair value as of the balance sheet date of the embedded derivative or group of embedded derivatives classified as a liability.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

Name:	us-gaap_EmbeddedDerivativeFairValueOfEmbeddedDerivativeLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant