Accounting Policies - Segment Reporting and Accounts Receivable (Details)	12 Months Ended
Dec. 31, 2020 USD ($) customer segment	Dec. 31, 2019 USD ($) customer
Concentration Risk [Line Items]
Number of reportable segments \| segment	2
Allowance for doubtful accounts \| $	$ 0	$ 0
Accounts Receivable \| Customer Concentration Risk
Concentration Risk [Line Items]
Number of customers \| customer	1	1
Concentration risk, percentage	49.90%	52.50%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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