Commercial Mortgage and Subordinate Loans, Net - Loan Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value	$ 4,828,046	$ 3,679,758
Commercial Mortgage Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value	3,723,550	2,653,826
Subordinate Mortgage Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying value	$ 1,104,496	$ 1,025,932

The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(c))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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