Transactions with Related Parties (Narrative) (Details) - Affiliated Entity - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Poseidon
Related Party Transaction [Line Items]
Related party transaction, revenues	$ 3,786	$ 3,147
Due from related parties	1,500		$ 2,600
Related party transaction, costs and expenses	240	254
Poseidon \| Asset Management Arrangement
Related Party Transaction [Line Items]
Related party transaction, revenues	2,400	2,300
ANSAC
Related Party Transaction [Line Items]
Related party transaction, revenues	67,955	73,079
Due from related parties	52,972		$ 43,400
Related party transaction, costs and expenses	$ 178	$ 832

For an unclassified balance sheet, amounts due from related parties including affiliates, employees, joint ventures, officers and stockholders, immediate families thereof, and pension funds.

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