Fair Value Measurements - Notional Amounts and Fair Values of Derivatives by Product (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional	$ 12,680	$ 729,500
Derivatives asset, Fair Value	14	4,873
Derivative liability, notional	5,201,134	5,317,805
Derivative liability, Fair Value	2,594	6,780
To Be Announced Security [Member] | Other Contracts
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional	12,680	729,500
Derivatives asset, Fair Value	14	4,873
Derivative liability, notional	19,180	200
Derivative liability, Fair Value	45	4
Other TBA Contracts [Member] | Other Contracts
Derivatives, Fair Value [Line Items]
Derivative liability, notional		729,500
Derivative liability, Fair Value		4,873
Future [Member] | Commodity Contracts
Derivatives, Fair Value [Line Items]
Derivative liability, notional	5,176,000	4,580,800	[1]
Derivative liability, Fair Value	1,781	807	[1]
Foreign exchange forward contracts | Other Contracts
Derivatives, Fair Value [Line Items]
Derivative liability, notional	400
Derivative liability, Fair Value	4
Auction Rate Securities Purchase Commitment | Other Contracts
Derivatives, Fair Value [Line Items]
Derivative liability, notional	5,554	7,305
Derivative liability, Fair Value	$ 764	$ 1,096

[1] For both the three and six months ended June 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 six months ended June 30, 2018).