Discontinued Operations (Details) $ in Thousands		3 Months Ended		12 Months Ended
	Jun. 02, 2016 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2016 USD ($)	Jun. 20, 2016 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent				83.68%
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners				16.32%
Proceeds from Divestiture of Businesses				$ 0	$ 45,448	$ 0
Dividends paid to noncontrolling interest				2,448	5,740	$ 0
Oppenheimer Multi Family Housing And Healthcare Finance [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of Loans Insured by U.S. Department of Housing and Development	480
Disposal Group, Including Discontinued Operation, Consideration							$ 3,800	$ 45,000
Disposal Group, Including Discontinued Operations, Consideration Withheld								$ 1,400
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax	$ 14,900
Dividends paid to noncontrolling interest				2,400	5,700
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries				12,600	$ 29,400
Payments for Repurchase of Preferred Stock and Preference Stock				$ 5,000
Business Pipeline of Mortgage Loans [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Divestiture of Businesses		$ 1,400	$ 1,500