Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financial assets
Derivative asset - current	$ 8,578	$ 43,888
Derivative asset - noncurrent	6,934	21,121
Financial liabilities
Derivative liability - current	176	528
Derivative liability - noncurrent	1,099	1,891
Fair Value on a Recurring Basis
Financial assets
Derivative asset - current	8,578	43,888
Derivative asset - noncurrent	6,934	21,121
Total financial assets	15,512	65,009
Financial liabilities
Derivative liability - current	176	528
Derivative liability - noncurrent	1,099	1,891
Total financial liabilities	1,275	2,419
Level 1 \| Fair Value on a Recurring Basis
Financial assets
Derivative asset - current	0	0
Derivative asset - noncurrent	0
Total financial assets	0	0
Financial liabilities
Derivative liability - current	0	0
Derivative liability - noncurrent	0	0
Total financial liabilities	0	0
Level 2 \| Fair Value on a Recurring Basis
Financial assets
Derivative asset - current	8,578	43,888
Derivative asset - noncurrent	6,934	21,121
Total financial assets	15,512	65,009
Financial liabilities
Derivative liability - current	176	528
Derivative liability - noncurrent	1,099	1,891
Total financial liabilities	1,275	2,419
Level 3 \| Fair Value on a Recurring Basis
Financial assets
Derivative asset - current	0	0
Derivative asset - noncurrent	0
Total financial assets	0	0
Financial liabilities
Derivative liability - current	0	0
Derivative liability - noncurrent	0	0
Total financial liabilities	$ 0	$ 0

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