Fair Value Measurement - (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	$ (37,253)	$ (7,551)
Level 1
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	2,196	7,187
Level 2
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	2,263	24,581
Level 3
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(41,712)	(39,319)
Money market funds
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		302
Money market funds | Level 1
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		302
Money market funds | Level 2
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		0
Money market funds | Level 3
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		0
Certificates of deposit
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		9,995
Certificates of deposit | Level 1
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		0
Certificates of deposit | Level 2
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		9,995
Certificates of deposit | Level 3
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		0
Commercial notes/bonds
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		6,775
Commercial notes/bonds | Level 1
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		0
Commercial notes/bonds | Level 2
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		6,775
Commercial notes/bonds | Level 3
Assets (liabilities) measured at fair value
Assets (liabilities), fair value		0
Commodity contract derivatives
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	4,459	14,696
Commodity contract derivatives | Level 1
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	2,196	6,885
Commodity contract derivatives | Level 2
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	2,263	7,811
Commodity contract derivatives | Level 3
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	0	0
Contingent Consideration for Acquisition | LS9, Inc
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(7,590)	(8,624)
Contingent Consideration for Acquisition | Dynamic Fuels, LLC
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(29,209)	(30,695)
Contingent Consideration for Acquisition | Imperium Renewables, Inc.
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(4,913)
Contingent Consideration for Acquisition | Level 1 | LS9, Inc
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	0	0
Contingent Consideration for Acquisition | Level 1 | Dynamic Fuels, LLC
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	0	0
Contingent Consideration for Acquisition | Level 1 | Imperium Renewables, Inc.
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	0
Contingent Consideration for Acquisition | Level 2 | LS9, Inc
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	0	0
Contingent Consideration for Acquisition | Level 2 | Dynamic Fuels, LLC
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	0	0
Contingent Consideration for Acquisition | Level 2 | Imperium Renewables, Inc.
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	0
Contingent Consideration for Acquisition | Level 3 | LS9, Inc
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(7,590)	(8,624)
Contingent Consideration for Acquisition | Level 3 | Dynamic Fuels, LLC
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	(29,209)	$ (30,695)
Contingent Consideration for Acquisition | Level 3 | Imperium Renewables, Inc.
Assets (liabilities) measured at fair value
Assets (liabilities), fair value	$ (4,913)