Derivative Instruments and Risk Management Activities - Assets and Liabilities Associated with Interest Rate Derivatives (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Assets from interest rate risk management activities:
Prepaid expenses and other current assets	$ 189	$ 444
Other assets	8,251	13,132
Total	8,440	13,576
Liabilities from interest rate risk management activities:
Accrued expenses and other current liabilities	254	115
Liabilities from interest rate risk management activities	2,430	1,696
Total	$ 2,684	$ 1,811

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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