Commitments and Contingencies - Accrued Limited Warranty (Details) $ in Millions	6 Months Ended
Jun. 30, 2018 USD ($) mi	Dec. 31, 2017 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Limited warranty, period	100 days
Limited warranty, miles \| mi	4,189
Accrued limited warranty \| $	$ 1.0	$ 0.8

Amount as of the balance sheet date of the aggregate standard product warranty liability. Does not include the balance for the extended product warranty liability.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (c)(1),(c)(5)
-URI http://asc.fasb.org/extlink&oid=68068213&loc=d3e12565-110249

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