Summary of Significant Accounting Policies - Inventory (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Inventory obsolescence charges	$ 321	$ 265	$ 502
Inventory obsolescence
Inventory obsolescence charges	$ 300	$ 300	$ 500

Amount of loss from reductions in inventory due to subsequent measurement adjustments, including, but not limited to, physical deterioration, obsolescence, or changes in price levels.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 330
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=116847112&loc=d3e4542-108314

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