Derivative Instruments - Impact of Netting Agreements and Margin Deposits (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Asset derivative instruments, at fair value
Gross derivative instruments, recorded in the Condensed Consolidated Balance Sheets	$ 370,254	$ 481,654
Liability derivative instruments, at fair value
Gross derivative instruments, recorded in the Condensed Consolidated Balance Sheets	308,607	336,051
Commodity derivatives
Asset derivative instruments, at fair value
Gross derivative instruments, recorded in the Condensed Consolidated Balance Sheets	370,254	481,654
Derivative instruments subject to master netting agreements	(200,252)	(256,087)
Margin deposits remitted to counterparties	0	0
Derivative instruments, net	170,002	225,567
Liability derivative instruments, at fair value
Gross derivative instruments, recorded in the Condensed Consolidated Balance Sheets	308,607	336,051
Derivative instruments subject to master netting agreements	(200,252)	(256,087)
Margin deposits remitted to counterparties	(7,917)	(40,283)
Derivative instruments, net	$ 100,438	$ 39,681

Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

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