Commercial Mortgage and Subordinate Loans, Net - Activity Relating to Loan Investment Portfolio (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Principal Balance
Loan repayments	$ (191,317)	$ (90,547)
Commercial Mortgage and Subordinated Portfolio Segment [Member]
Principal Balance
Principal balance, beginning	4,982,514
New loan fundings	441,844
Add-on loan fundings	110,331
Loan repayments	(322,354)
Gain (loss) on foreign currency translation	15,033
PIK interest and amortization of fees	14,321
Principal balance, ending	5,241,689
Deferred Fees/Other Items
Deferred fees/other items, beginning	(17,940)
Gain (loss) on foreign currency translation	(136)
Deferred fees	(6,069)
PIK interest and amortization of fees	6,436
Deferred fees/other items, ending	(17,709)
Provision for Loan Loss
Provision for loans, beginning	(36,981)
Provision for loans, ending	(36,981)
Carrying Value
Carrying value, beginning balance	4,927,593
Gain (loss) on foreign currency translation	14,897
Deferred fees	(6,069)
PIK interest and amortization of fees	20,757
Carrying value, ending balance	5,186,999
Other Assets [Member] \| Commercial Mortgage and Subordinated Portfolio Segment [Member]
Carrying Value
Impairment	$ 3,000

Loan and Leases Receivable, Deferred income [Roll Forward]

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Loan and Leases Receivable, Gross [Roll Forward]

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Loan and Leases Receivable, Net [Roll Forward]

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Loans and Leases Receivable, Deferred Income, Amortization

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Loans and Leases Receivable, Deferred Income, Period Increase

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Loans and Leases Receivable, Deferred Income, Unamortized Loan Commitment and Origination Fees, and Unamortized Discounts or Premiums, Period Increase

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Loans and Leases Receivable, Deferred Income, Unrealized Gain On Foreign Currency Translation

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Loans and Leases Receivable, Gross, Foreign Currency Gain (Loss)

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Loans and Leases Receivable, Gross, Paid-in-Kind Interest, Loan Commitment and Origination Fees, and Discounts or Premiums, Amortization

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Loans and Leases Receivable, Net, Deferred Income, PIK Interest, Loan Commitment and Origination Fees, and Discounts or Premiums, Amortization

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Loans and Leases Receivable, Net, Foreign Currency Gain (Loss)

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Mortgage Loans on Real Estate, Impairment

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Payments to Purchase Loans Held-for-sale, Add-on Funding

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount of deferred interest and fee income, unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of acquired loans. Excludes amounts for loans and leases covered under loss sharing agreements.

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

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The cash inflow from collection of repayments from borrowers on loans that are secured with real estate mortgages and are held with the intention to resell in the near future.

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