Financial Instruments and Fair Value Measurements - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2014	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Retained interest promissory note receivable	$ 15,000,000		$ 15,000,000
Notes, maturity period			15 years
Other than temporary impairment related to retained interest investments	0	$ 0	$ 0	$ 0
Debt principal amount					$ 180,000,000.0
Debt interest rate					4.80%
Senior Notes Held By Special Purpose Entity	176,255,000		176,255,000			$ 176,094,000
Unamortized discount and debt issuance costs	635,000		635,000			720,000
Carrying Value | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Retained interest, fair value	10,494,000		10,494,000			10,246,000
Senior Notes Held By Special Purpose Entity	176,255,000		176,255,000			$ 176,094,000
AgReserves Sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Note received in sale of real estate					$ 200,000,000
Maturity of installment note					15 years
Subsidiaries | Notes Receivable
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Issue price of Senior Secured Notes					98.50%
Buyer Special Purpose Entity
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Time Deposits Held By Special Purpose Entities	200,000,000		200,000,000
Special Purpose Entities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. Treasuries Held By Special Purpose Entities	8,100,000		8,100,000
Cash Held By Special Purpose Entities	400,000		400,000
Senior Notes Held By Special Purpose Entity	176,300,000		176,300,000
Unamortized discount and debt issuance costs	$ 3,700,000		$ 3,700,000
Special Purpose Entities | Notes Receivable
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt interest rate	4.00%		4.00%
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Note maturity year			2022
Retained interest, effective interest rate			3.70%
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Note maturity year			2024
Retained interest, effective interest rate			11.30%