Fair Value Measurements - Notional Amounts and Fair Values of Derivatives by Product (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands		Dec. 31, 2017		Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional		$ 65,576	[1]	$ 297,727	[2]
Derivatives asset, Fair Value		716	[1]	1,663	[2]
Derivative liability, notional		5,920,568	[1]	4,756,631	[2]
Derivative liability, Fair Value		1,388	[1]	2,024	[2]
Other Contracts | TBA
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional		26,000	[1]	169,500	[2]
Derivatives asset, Fair Value		22	[1]	332	[2]
Derivative liability, notional		26,000	[1]	169,500	[2]
Derivative liability, Fair Value		22	[1]	289	[2]
Other Contracts | TBA Sale Agreements
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional		39,576	[1]	121,573	[2]
Derivatives asset, Fair Value		694	[1]	482	[2]
Derivative liability, notional				121,573
Derivative liability, Fair Value				923
Other Contracts | Foreign currency forward contracts
Derivatives, Fair Value [Line Items]
Derivative liability, notional	[1]			200
Derivative liability, Fair Value	[1]			1
Other Contracts | Auction Rate Securities Purchase Commitment
Derivatives, Fair Value [Line Items]
Derivatives asset, Notional	[1]			6,654
Derivatives asset, Fair Value	[1]			849
Derivative liability, notional		10,992	[1]	24,358	[2]
Derivative liability, Fair Value		8	[1]	645	[2]
Other Contracts | TBA Purchase Agreements [Member] [Member]
Derivatives, Fair Value [Line Items]
Derivative liability, notional	[1]	39,576
Derivative liability, Fair Value	[1]	592
Other Contracts | Forward Start Repurchase Agreement [Member]
Derivatives, Fair Value [Line Items]
Derivative liability, notional	[2]			382,000
Derivative liability, Fair Value	[2]			0
Commodity Contracts | Futures
Derivatives, Fair Value [Line Items]
Derivative liability, notional		5,844,000	[1],[3]	4,059,000	[2],[4]
Derivative liability, Fair Value		$ 766	[1],[3]	$ 166	[2],[4]

[1] )See "Derivative Instruments and Hedging Activities" above for a description of derivative financial instruments.

[2] )See "Derivative Instruments and Hedging Activities" above for a description of derivative financial instruments.

[3] 2)Represents TBA purchase and sale contracts related to the legacy OMHHF business.

[4] For the year ended December 31, 2017, the diluted earnings per share computation does not include the anti-dilutive effect of 10,592 shares of Class A Stock granted under share-based compensation arrangements (1,237,134 and 1,269,585 shares for the years ended December 31, 2016 and 2015, respectively).(2)Represents net income from discontinued operations less net income attributable to noncontrolling interest, net of tax divided by weighted average number of shares outstanding.