Transactions with Related Parties (Narrative) (Details) - Affiliated Entity - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Poseidon
Related Party Transaction [Line Items]
Due from related parties	$ 2,400		$ 2,400		$ 2,400
Related party transaction, revenues	3,236	$ 3,039	6,401	$ 6,239
Related party transaction, costs and expenses	255	250	502	499
Poseidon \| Asset Management Arrangement
Related Party Transaction [Line Items]
Related party transaction, revenues	2,200	2,200	4,500	4,300
ANSAC
Related Party Transaction [Line Items]
Due from related parties	58,871		58,871		$ 60,594
Related party transaction, revenues	81,784	93,938	172,463	184,734
Related party transaction, costs and expenses	$ 1,279	$ 1,256	$ 2,336	$ 3,034

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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