Income Taxes - Operating Loss Carryforwards (Details) $ in Millions	Dec. 31, 2017 USD ($)
State
Net operating loss carryforwards
Net operating loss carryforwards	$ 23.2
Foreign \| German Trade Tax
Net operating loss carryforwards
Net operating loss carryforwards	77.4
Foreign \| Other foreign countries
Net operating loss carryforwards
Net operating loss carryforwards	$ 13.9

Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32559-109319

Name:	us-gaap_OperatingLossCarryforwards
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant