Debt - Aggregate principal amount and interest rates (Details) - Notes payable to finance companies for insurance - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
DEBT
Aggregate principal amount outstanding	$ 40	$ 1,746
Interest rate (as a percent)	4.99%
Minimum
DEBT
Interest rate (as a percent)		4.05%
Maximum
DEBT
Interest rate (as a percent)		4.99%

Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant