Transactions with Related Parties (Narrative) (Details) - Affiliated Entity - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Poseidon
Related Party Transaction [Line Items]
Due from related parties	$ 1,900		$ 1,900		$ 2,400
Related party transaction, revenues	3,019	$ 3,021	9,420	$ 9,260
Related party transaction, costs and expenses	240	247	742	746
Poseidon \| Asset Management Arrangement
Related Party Transaction [Line Items]
Related party transaction, revenues	2,200	2,200	6,700	6,500
ANSAC
Related Party Transaction [Line Items]
Due from related parties	70,237		70,237		$ 60,594
Related party transaction, revenues	99,878	90,433	272,341	275,167
Related party transaction, costs and expenses	$ 1,020	$ 1,393	$ 3,356	$ 4,427

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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