Commercial Mortgage Loans - Narrative (Details) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2020 USD ($) loan	Dec. 31, 2019 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	$ 21,702	$ 921
Initial risk rating	2.0
Weighted average risk rating of loans	2.3	2.1
Real estate owned, net of depreciation	$ 49,306	$ 35,333
Commercial Mortgage Receivable, Held-For-Sale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of mezzanine loans funded \| loan	8	7
Par Value	$ 93,668	$ 112,488
Commercial Mortgage Receivable, Held-For-Investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of mezzanine loans funded \| loan	118	122
Par Value	$ 2,670,133	$ 2,771,299
Real Estate Acquired in Satisfaction of Debt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision/(recovery) for credit losses, net	400
Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision/(recovery) for credit losses, net	13,997
Commercial Mortgage Receivable, Held-For-Investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans written-off	0	$ 14,937
Real estate owned, net of depreciation	14,000
Commercial Mortgage Receivable, Held-For-Investment \| Land, Buildings and Improvements
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real estate owned, net of depreciation	11,600
Commercial Mortgage Receivable, Held-For-Investment \| Furniture and Fixtures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real estate owned, net of depreciation	2,400
Commercial Mortgage Receivable, Held-For-Investment \| Real Estate Acquired in Satisfaction of Debt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans written-off	14,400
Commercial Mortgage Receivable, Held-For-Investment \| Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Par Value	$ 2,662,681
Commercial Mortgage Receivable, Held-For-Investment \| Commercial Portfolio Segment \| Nonperforming Financial Instruments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of mezzanine loans funded \| loan	2	1
Cost basis		$ 57,100
Commercial Mortgage Receivable, Held-For-Investment \| Commercial Portfolio Segment \| Loan One
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost basis	$ 57,100
Commercial Mortgage Receivable, Held-For-Investment \| Commercial Portfolio Segment \| Loan Two
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost basis	$ 45,300

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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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