Summary of Significant Accounting Policies (Details) - USD ($)			1 Months Ended		3 Months Ended		6 Months Ended
	Oct. 31, 2015	Jul. 31, 2015	Sep. 30, 2015	Apr. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Jun. 02, 2016	Mar. 31, 2016	Dec. 31, 2015	Feb. 28, 2015
Business Acquisition [Line Items]
Biomass-based diesel government incentives					$ 97,153,000	$ 7,278,000	$ 155,554,000	$ 17,066,000
Accounts receivable, net					97,493,000		97,493,000				$ 310,731,000
Estimated impaired fixed assets			$ 1,414,000	$ 11,027,000			15,567,000
Insurance recoveries							17,600,000
Gain on involuntary conversion					997,000	$ 0	4,540,000	0
Change in fair value of convertible debt conversion liability					13,432,000		(13,432,000)	$ 0
February 2015
Business Acquisition [Line Items]
Share repurchase program, amount authorized to be repurchased												$ 30,000,000
Stock repurchase program, amount repurchased					$ 870,000		6,687,000
Stock repurchase program, shares repurchased (in shares)					90,654
March 2016
Business Acquisition [Line Items]
Share repurchase program, amount authorized to be repurchased										$ 50,000,000
Stock repurchase program, amount repurchased					$ 38,429,000		$ 38,429,000
Stock repurchase program, shares repurchased (in shares)					4,442,823		4,442,823
2036 Convertible Notes | Convertible Debt
Business Acquisition [Line Items]
Face amount					$ 152,000,000		$ 152,000,000		$ 152,000,000
Interest rate					4.00%		4.00%
Stock repurchase program, shares repurchased (in shares)							4,060,323
Services
Business Acquisition [Line Items]
Minimum percentage of increase in fair value of goodwill over carrying value	24.00%	21.00%
Biodiesel Mixture Excise Tax Credit
Business Acquisition [Line Items]
Biomass-based diesel government incentives							$ 242,139,000
Accounts receivable, net					$ 1,650,000		$ 1,650,000