Number of shares of equity interests issuable upon contingent consideration in business acquisition.

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The number of common stock per unit.

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The number of units outstanding as of the reporting date.

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Number of shares issued during the period through an agent under an "at the market" equity offering program agreement.

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Number of shares of equity interests issued or issuable to acquire entity.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Aggregate dividends declared during the period for each share of common stock outstanding.

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The value of the financial instrument(s) that the original debt is being converted into in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

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Amount of investment in marketable security.

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Carrying amount of the equity interests owned by noncontrolling shareholders, partners, or other equity holders in joint ventures included in the entity's consolidated financial statements.

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The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

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Amount of Net Income (Loss) attributable to noncontrolling interest.

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The cash outflow to reacquire common stock during the period.

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Amount of cash outflow to a noncontrolling interest. Includes, but not limited to, reduction of noncontrolling interest ownership. Excludes dividends paid to the noncontrolling interest.

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Number of stock bought back by the entity at the exercise price or redemption price.

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Stockholders' Equity and Non-Controlling Interests (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2018	Dec. 31, 2019
Stockholders' Equity
Dividend declared (in dollars per share)	$ 0.48	$ 0.48
Shares issued under ATM Agreement	0	0
Repurchase of common stock		$ 28,830
Net income attributable to non-controlling interests	$ 11,148	500
Investment securities	678,287		$ 736,658
Accrued interest receivable	101,713		95,980
Payment to acquire non-controlling interest	$ 8,833	66,476
CMBS JV
Stockholders' Equity
Noncontrolling Interest, Ownership Percentage by Parent	51.00%
Class A Units
Stockholders' Equity
Number of units outstanding	10,600,000
Value of shares issued to settle redemption	$ 100
CMBS JV
Stockholders' Equity
Non-controlling interest	132,400		$ 126,700
CMBS JV \| Joint Venture Partner
Stockholders' Equity
Equity Method Investment, Ownership Percentage					49.00%
Woodstar II Portfolio \| Class A Units
Stockholders' Equity
Net income attributable to non-controlling interests	$ 5,100
Woodstar II Portfolio \| Class A Units \| SPT Dolphin
Stockholders' Equity
Shares issued				10,200,000
Right to receive additional shares	1,900,000			1,900,000
Number of common stock per unit	1
Woodstar II Portfolio \| Class A Units \| SPT Dolphin \| Non-Controlling Interests
Stockholders' Equity
Redemption of units	225,600,000		226,700,000
Woodstar II Portfolio \| CMBS JV \| Class A Units
Stockholders' Equity
Net income attributable to non-controlling interests	$ 5,400	$ (6,000)