Marketable Securities Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Marketable Securities [Abstract]
Interest income, money market deposits	$ 267	$ 2	$ 299	$ 17

Interest earned on funds deposited in US domestic money market accounts.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.4)
-URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260

Name:	us-gaap_InterestIncomeMoneyMarketDeposits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration