Fair Value Measures and Disclosures (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Level 1 inputs
Fair Value, Assets Measured on Recurring Basis
Fair value of equity investment in TuSimple	$ 13,129	$ 0

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as noncurrent.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=123594786&loc=SL75136599-209740

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