Commitments And Contingencies Commitments and Contingencies (Details)	6 Months Ended
	Jun. 30, 2017 USD ($)
Other Commitments [Line Items]
Capital commitment	$ 5,000,000
Flow agreement March 2015 with mortgage originator [Member]
Other Commitments [Line Items]
Purchase commitment	200,000,000
Purchases made in connection with purchase commitments	168,900,000
Related Party A [Member] | Non-Exchange Traded Equity Investment in Mortgage Originator
Other Commitments [Line Items]
Guaranty Liabilities	125,000,000
Drawn down amount being guaranteed	47,300,000
Guarantor Obligations, Current Carrying Value	0
Related Party B [Member] | Non-Exchange Traded Equity Investment in Mortgage Originator
Other Commitments [Line Items]
Guaranty Liabilities	15,000,000
Drawn down amount being guaranteed	0
Guarantor Obligations, Current Carrying Value	$ 0