Derivative Instruments and Fair Value Measurements - Derivatives by Hedging Relationship and Fair Value Measurements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Derivatives:
Loss on deconsolidation of subsidiary (Note 3)	$ 1,870	$ 0	$ 3,505	$ 0
Fair Value, Measurements, Recurring
Derivatives:
Current assets					$ 112
Current assets, counterparty offsets					(266)
Current liabilities					(64)
Current liabilities, counterparty offsets					266
Net value					48
Net value, counterparty offsets					0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1)
Derivatives:
Current assets					0
Current liabilities					0
Net value					0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Derivatives:
Current assets					378
Current liabilities					(330)
Net value					48
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 [Member]
Derivatives:
Current assets					0
Current liabilities					0
Net value					$ 0
Fair Value, Measurements, Nonrecurring
Derivatives:
Loss on deconsolidation of subsidiary (Note 3)			6,005
AREC [Member] | Fair Value, Measurements, Nonrecurring
Derivatives:
Investment in AREC	3,200		3,200
Loss on deconsolidation of subsidiary (Note 3)			3,505
AREC [Member] | Fair Value, Measurements, Nonrecurring | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1)
Derivatives:
Investment in AREC	0		0
AREC [Member] | Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 3)
Derivatives:
Investment in AREC	3,200		3,200
AREC [Member] | Fair Value, Measurements, Nonrecurring | Fair Value, Inputs, Level 3 [Member]
Derivatives:
Investment in AREC	0		0
VestaCare, Inc. [Member] | Fair Value, Measurements, Nonrecurring
Derivatives:
Investment in AREC	0		0
Loss on deconsolidation of subsidiary (Note 3)			2,500
VestaCare, Inc. [Member] | Fair Value, Measurements, Nonrecurring | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1)
Derivatives:
Investment in AREC	0		0
VestaCare, Inc. [Member] | Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 3)
Derivatives:
Investment in AREC	0		0
VestaCare, Inc. [Member] | Fair Value, Measurements, Nonrecurring | Fair Value, Inputs, Level 3 [Member]
Derivatives:
Investment in AREC	0		0
Commodity Contract | Revenues - Marketing | Not Designated as Hedging Instrument
Derivative, Gain (Loss) on Derivative, Net [Abstract]
Revenues – Marketing	$ (748)	$ 180	$ (48)	$ 304