Summary of Significant Accounting Policies - Research and Development (Details 6) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Research and Development
Reimbursements received from customers	$ 4,299	$ 2,036	$ 1,861
Other Current Assets
Research and Development
Cost of molds, dies and other tools included in other current assets	$ 3,382	$ 2,837

Carrying amount as of the balance sheet date of capitalized costs of molds, dies, and other tools that will be used in producing products under a long-term supply arrangement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 10
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6387057&loc=d3e6169-108318

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=27011391&loc=d3e105117-122735

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