Fair Value Measurements - Notional Amounts and Fair Values of Derivatives by Product (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional	$ 596,931	$ 65,576
Derivatives asset, Fair Value	12,309	716
Derivative liability, notional	4,324,364	5,920,568
Derivative liability, Fair Value	14,048	1,388
To Be Announced Security [Member] | Other Contracts
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional	568,430	26,000
Derivatives asset, Fair Value	11,057	22
Derivative liability, notional	568,430	26,000
Derivative liability, Fair Value	11,068	22
Other TBA Contracts [Member] | Other Contracts
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional	28,501	39,576
Derivatives asset, Fair Value	1,252	694
Derivative liability, notional	28,501	39,576
Derivative liability, Fair Value	1,190	592
Future [Member] | Commodity Contracts
Derivatives, Fair Value [Line Items]
Derivative liability, notional	3,720,000	5,844,000	[1]
Derivative liability, Fair Value	709	766	[1]
Foreign exchange forward contracts | Other Contracts
Derivatives, Fair Value [Line Items]
Derivative liability, notional	200
Derivative liability, Fair Value	2
Auction Rate Securities Purchase Commitment | Other Contracts
Derivatives, Fair Value [Line Items]
Derivative liability, notional	7,233	10,992
Derivative liability, Fair Value	$ 1,079	$ 8

[1] For both the three and nine months ended September 30, 2018, the diluted net income per share computation does not include the anti-dilutive effect of 4,050 shares of Class A Stock granted under share-based compensation arrangements (15,450 shares for both the three and nine months ended September 30, 2017).(2)Represents net income from discontinued operations less net income attributable to non-controlling interest, net of tax divided by weighted average number of shares outstanding.