Fair Value Measurements - Notional Amounts and Fair Values of Derivatives by Product (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional	$ 15,742	$ 729,500
Derivatives asset, Fair Value	12	4,873
Derivative liability, notional	2,865,250	5,317,805
Derivative liability, Fair Value	1,337	6,780
To Be Announced Security [Member] | Other Contracts
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional	15,742	729,500
Derivatives asset, Fair Value	12	4,873
Derivative liability, notional	12,240	729,500
Derivative liability, Fair Value	9	4,873
Future [Member] | Commodity Contracts
Derivatives, Fair Value [Line Items]
Derivative liability, notional	2,846,000	4,580,800	[1]
Derivative liability, Fair Value	322	807	[1]
Foreign exchange forward contracts | Other Contracts
Derivatives, Fair Value [Line Items]
Derivative liability, notional		200
Derivative liability, Fair Value		4
Auction Rate Securities Purchase Commitment | Other Contracts
Derivatives, Fair Value [Line Items]
Derivative liability, notional	7,010	7,305
Derivative liability, Fair Value	$ 1,006	$ 1,096

[1] For both the three and nine months ended September 30, 2019, the diluted net income per share computation does not include the anti-dilutive effect of 7,628 shares of Class A Stock granted under share-based compensation arrangements (4,050 shares for both the three and nine months ended September 30, 2018).