Revenue from Contracts with Customers (Contract with Customer, Asset and Liability) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Contract liability	$ 9,173	$ 9,881
Mid-Stream [Member]
Disaggregation of Revenue [Line Items]
Contract assets	13,155	13,164
Amounts invoiced in excess of revenue recognized	(9)
Contract with Customer, Asset, Net, Current	1,800	300
Contract with Customer, Asset, Net, Noncurrent	11,400	12,900
Contract liability	9,173	9,882
Contract with Customer, Liability, Revenue Recognized	(709)
Contract with Customer, Liability, Current	2,900	2,900
Contract with Customer, Liability, Noncurrent	$ 6,300	$ 7,000

Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current.

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