Revenue Recognition - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation Of Revenue [Line Items]
Cost of sales	$ 92,569	$ 96,960	$ 198,022	$ 191,771
Shipments [Member] \| Selling General and Administrative Expenses [Member]
Disaggregation Of Revenue [Line Items]
Cost of sales	2,600	2,000	5,300	4,300
Shipments [Member] \| Cost of Sales [Member]
Disaggregation Of Revenue [Line Items]
Cost of sales	$ 1,400	$ 1,500	$ 2,800	$ 3,000

The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.2(a),(d))
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

Name:	us-gaap_CostOfGoodsAndServicesSold
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration