Fair Value Measurements (Assets and Liabilities Measured on Recurring Basis) (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Assets and liabilities measured at fair value on a recurring basis
Commodity derivatives, net	[1]	$ 165,823	$ 18,365	$ (33,095)
Provisionally price contracts	[2]	(39,279)	(134,741)	(62,298)
Convertible preferred securities	[3]	8,404	7,154	7,488
Other assets and liabilities	[4]	(5,466)	4,833	4,099
Total		129,482	(104,389)	(83,806)
Level 1
Assets and liabilities measured at fair value on a recurring basis
Commodity derivatives, net	[1]	103,350	37,229	15,356
Provisionally price contracts	[2]	(1,064)	(76,175)	(37,787)
Convertible preferred securities	[3]	0	0	0
Other assets and liabilities	[4]	5,284	5,186	4,136
Total		107,570	(33,760)	(18,295)
Level 2
Assets and liabilities measured at fair value on a recurring basis
Commodity derivatives, net	[1]	62,473	(18,864)	(48,451)
Provisionally price contracts	[2]	(38,215)	(58,566)	(24,511)
Convertible preferred securities	[3]	0	0	0
Other assets and liabilities	[4]	(10,750)	(353)	(37)
Total		13,508	(77,783)	(72,999)
Level 3
Assets and liabilities measured at fair value on a recurring basis
Commodity derivatives, net	[1]	0	0	0
Provisionally price contracts	[2]	0	0	0
Convertible preferred securities	[3]	8,404	7,154	7,488
Other assets and liabilities	[4]	0	0	0
Total		$ 8,404	$ 7,154	$ 7,488

[1] Includes associated cash posted/received as collateral

[2] Included in "Provisionally priced contracts" are those instruments based only on underlying futures values (Level 1) and delayed price contracts (Level 2)

[3] Recorded in “Other noncurrent assets” on the Company’s Condensed Consolidated Balance Sheets.

[4] Included in other assets and liabilities are assets held in rabbi trusts to fund deferred compensation plans, ethanol risk management contracts, and foreign exchange derivative contracts (Level 1), and interest rate derivatives (Level 2).