Fair Value Measurement - Financial Instruments Carried at Fair Value by Consolidated Balance Sheet Caption and by Valuation Hierarchy (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Valuation Hierarchy
Current assets	$ 7,590	$ 24,100
Long-term assets	1,608	34,744
Current liabilities	15,696	14,650
Long-term liabilities	5,355	1,209
Recurring | Commodity derivatives
Valuation Hierarchy
Current assets	7,590	24,100
Long-term assets	1,608	34,744
Current liabilities	15,696	14,650
Long-term liabilities	5,355	1,209
Recurring | Level 2 | Commodity derivatives
Valuation Hierarchy
Current assets	7,590	24,100
Long-term assets	(344)	36,384
Current liabilities	14,587	13,636
Long-term liabilities	4,250	892
Recurring | Level 3 | Commodity derivatives
Valuation Hierarchy
Long-term assets	1,952	(1,640)
Current liabilities	1,109	1,014
Long-term liabilities	$ 1,105	$ 317