Fair Value Measurements - Notional Amounts and Fair Values of Derivatives by Product (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional	$ 22,885
Derivatives asset, Fair Value	275
Derivative liability, notional	3,650,876	$ 5,229,373
Derivative liability, Fair Value	528	1,414
To Be Announced Security [Member] | Other Contracts
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional	22,885
Derivatives asset, Fair Value	275
Derivative liability, notional	19,585	13,245
Derivative liability, Fair Value	220	124
Future [Member] | Commodity Contracts
Derivatives, Fair Value [Line Items]
Derivative liability, notional	3,630,000	5,209,000	[1]
Derivative liability, Fair Value	116	267	[1]
Auction Rate Securities Purchase Commitment | Other Contracts
Derivatives, Fair Value [Line Items]
Derivative liability, notional	1,291	7,128
Derivative liability, Fair Value	$ 192	$ 1,023

[1] For both the three and nine months ended September 30, 2020, the diluted earnings per share computation does not include the anti-dilutive effect of 10,770 shares of Class A Stock granted under share-based compensation arrangements (7,628 shares for both the three and nine months ended September 30, 2019).