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Commitments and Contingencies (Details)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) claim
Commitments and Contingencies
Co-investment commitments in partnership			$ 97,100,000
Prior Owner
Commitments and Contingencies
Reimbursable amount of investment commitments			11,000,000
Consolidated Affiliates
Commitments and Contingencies
Contingent liability			84,900,000
Expected payments of contingent liability			10,300,000
Present value of expected payments of contingent liabilities			8,900,000
Consolidated Affiliates | Scenario, Forecast
Commitments and Contingencies
Contingent liability		$ 57,500,000
Expected payments of contingent liability	$ 3,000,000
Equity Method Investee
Commitments and Contingencies
Contingent liability			$ 170,000,000
Equity Method Investee | Scenario, Forecast
Commitments and Contingencies
Expected payments of contingent liability	$ 0
Third Avenue Focused Credit Fund | Affiliated Entity | Third Avenue
Commitments and Contingencies
Number of pending claims | claim				1
Loss contingency reserve				$ 15,000,000

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- Definition

-- None. No documentation exists for this element. --

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- Definition

The amount that the entity agreed to co-invest in certain investment partnerships where the entity serves as the general partner.

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Other Commitment Expected Payments

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Other Commitment Present Value of Expected Payments

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- Definition

Represents the contractual obligation to reimburse the entity for co-investments in investment partnerships.

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- Definition

Amount of loss contingency liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

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Number of pending claims pertaining to a loss contingency.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

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Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

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No definition available.

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