Commercial Mortgage Loans - Internal Credit Qualities (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 5,328,273	$ 4,226,888
Commercial Mortgage Receivable, Held-For-Investment
Financing Receivable, Credit Quality Indicator [Line Items]
Total	5,350,728	4,242,962
Commercial Mortgage Receivable, Held-For-Investment | Multifamily
Financing Receivable, Credit Quality Indicator [Line Items]
Total	3,992,990	2,953,938
Commercial Mortgage Receivable, Held-For-Investment | Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Total	172,503	104,990
Commercial Mortgage Receivable, Held-For-Investment | Office
Financing Receivable, Credit Quality Indicator [Line Items]
Total	456,866	485,575
Commercial Mortgage Receivable, Held-For-Investment | Industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	93,035	88,956
Commercial Mortgage Receivable, Held-For-Investment | Mixed Use
Financing Receivable, Credit Quality Indicator [Line Items]
Total	52,500	62,965
Commercial Mortgage Receivable, Held-For-Investment | Hospitality
Financing Receivable, Credit Quality Indicator [Line Items]
Total	503,251	460,884
Commercial Mortgage Receivable, Held-For-Investment | Self Storage
Financing Receivable, Credit Quality Indicator [Line Items]
Total	44,895	56,495
Commercial Mortgage Receivable, Held-For-Investment | Manufactured Housing
Financing Receivable, Credit Quality Indicator [Line Items]
Total	34,688	29,159
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	1,767,125	2,729,537
Year two, originated in prior fiscal year one	2,665,468	689,545
Year three, originated in prior fiscal year two	433,029	475,252
Year four, originated in prior fiscal year three	254,929	253,452
Year five, original in prior fiscal year four	128,794	79,102
Year six, originated in prior fiscal year five	78,928
Total	5,328,273	4,226,888
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | Multifamily
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	1,402,934	2,438,376
Year two, originated in prior fiscal year one	2,371,872	270,953
Year three, originated in prior fiscal year two	103,681	103,989
Year four, originated in prior fiscal year three	24,058	127,902
Year five, original in prior fiscal year four	74,876	0
Year six, originated in prior fiscal year five	0
Total	3,977,421	2,941,220
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	126,439	33,830
Year two, originated in prior fiscal year one	33,870	11,928
Year three, originated in prior fiscal year two	0	29,515
Year four, originated in prior fiscal year three	8,203	29,452
Year five, original in prior fiscal year four	0	0
Year six, originated in prior fiscal year five	0
Total	168,512	104,725
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | Office
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	0	50,291
Year two, originated in prior fiscal year one	50,343	253,759
Year three, originated in prior fiscal year two	240,183	136,800
Year four, originated in prior fiscal year three	133,888	43,308
Year five, original in prior fiscal year four	31,723	0
Year six, originated in prior fiscal year five	0
Total	456,137	484,158
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | Industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	77,712	0
Year two, originated in prior fiscal year one	0	31,906
Year three, originated in prior fiscal year two	14,946	56,933
Year four, originated in prior fiscal year three	0	0
Year five, original in prior fiscal year four	0	0
Year six, originated in prior fiscal year five	0
Total	92,658	88,839
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | Mixed Use
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	19,926	32,395
Year two, originated in prior fiscal year one	32,446	30,325
Year three, originated in prior fiscal year two	0	0
Year four, originated in prior fiscal year three	0	0
Year five, original in prior fiscal year four	0	0
Year six, originated in prior fiscal year five	0
Total	52,372	62,720
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | Hospitality
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	129,645	153,032
Year two, originated in prior fiscal year one	155,287	26,920
Year three, originated in prior fiscal year two	26,956	148,015
Year four, originated in prior fiscal year three	88,780	52,790
Year five, original in prior fiscal year four	22,195	79,102
Year six, originated in prior fiscal year five	78,928
Total	501,791	459,859
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | Self Storage
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	0	14,948
Year two, originated in prior fiscal year one	14,976	41,382
Year three, originated in prior fiscal year two	29,846	0
Year four, originated in prior fiscal year three	0	0
Year five, original in prior fiscal year four	0	0
Year six, originated in prior fiscal year five	0
Total	44,822	56,330
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | Manufactured Housing
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	10,469	6,665
Year two, originated in prior fiscal year one	6,674	22,372
Year three, originated in prior fiscal year two	17,417	0
Year four, originated in prior fiscal year three	0	0
Year five, original in prior fiscal year four	0	0
Year six, originated in prior fiscal year five	0
Total	34,560	29,037
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | 1-2 internal grade | Multifamily
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	1,402,934	2,438,376
Year two, originated in prior fiscal year one	2,276,836	270,953
Year three, originated in prior fiscal year two	92,829	103,989
Year four, originated in prior fiscal year three	0	90,877
Year five, original in prior fiscal year four	37,851	0
Year six, originated in prior fiscal year five	0
Total	3,810,450	2,904,195
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | 1-2 internal grade | Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	20,941	33,830
Year two, originated in prior fiscal year one	33,870	11,928
Year three, originated in prior fiscal year two	0	29,515
Year four, originated in prior fiscal year three	8,203	29,452
Year five, original in prior fiscal year four	0	0
Year six, originated in prior fiscal year five	0
Total	63,014	104,725
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | 1-2 internal grade | Office
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	0	50,291
Year two, originated in prior fiscal year one	50,343	253,759
Year three, originated in prior fiscal year two	203,840	136,800
Year four, originated in prior fiscal year three	108,152	43,308
Year five, original in prior fiscal year four	18,746	0
Year six, originated in prior fiscal year five	0
Total	381,081	484,158
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | 1-2 internal grade | Industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	77,712	0
Year two, originated in prior fiscal year one	0	31,906
Year three, originated in prior fiscal year two	14,946	0
Year four, originated in prior fiscal year three	0	0
Year five, original in prior fiscal year four	0	0
Year six, originated in prior fiscal year five	0
Total	92,658	31,906
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | 1-2 internal grade | Mixed Use
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	19,926	32,395
Year two, originated in prior fiscal year one	32,446	30,325
Year three, originated in prior fiscal year two	0	0
Year four, originated in prior fiscal year three	0	0
Year five, original in prior fiscal year four	0	0
Year six, originated in prior fiscal year five	0
Total	52,372	62,720
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | 1-2 internal grade | Hospitality
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	129,645	153,032
Year two, originated in prior fiscal year one	155,287	26,920
Year three, originated in prior fiscal year two	26,956	34,054
Year four, originated in prior fiscal year three	58,814	0
Year five, original in prior fiscal year four	22,195	0
Year six, originated in prior fiscal year five	0
Total	392,897	214,006
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | 1-2 internal grade | Self Storage
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	0	14,948
Year two, originated in prior fiscal year one	14,976	41,382
Year three, originated in prior fiscal year two	29,846	0
Year four, originated in prior fiscal year three	0	0
Year five, original in prior fiscal year four	0	0
Year six, originated in prior fiscal year five	0
Total	44,822	56,330
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | 1-2 internal grade | Manufactured Housing
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	10,469	6,665
Year two, originated in prior fiscal year one	6,674	22,372
Year three, originated in prior fiscal year two	17,417	0
Year four, originated in prior fiscal year three	0	0
Year five, original in prior fiscal year four	0	0
Year six, originated in prior fiscal year five	0
Total	34,560	29,037
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | 3-4 internal grade | Multifamily
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	0	0
Year two, originated in prior fiscal year one	95,036	0
Year three, originated in prior fiscal year two	10,852	0
Year four, originated in prior fiscal year three	24,058	37,025
Year five, original in prior fiscal year four	37,025	0
Year six, originated in prior fiscal year five	0
Total	166,971	37,025
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | 3-4 internal grade | Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	0	0
Year two, originated in prior fiscal year one	0	0
Year three, originated in prior fiscal year two	0	0
Year four, originated in prior fiscal year three	0	0
Year five, original in prior fiscal year four	0	0
Year six, originated in prior fiscal year five	0
Total	0	0
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | 3-4 internal grade | Office
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	0	0
Year two, originated in prior fiscal year one	0	0
Year three, originated in prior fiscal year two	36,343	0
Year four, originated in prior fiscal year three	25,736	0
Year five, original in prior fiscal year four	12,977	0
Year six, originated in prior fiscal year five	0
Total	75,056	0
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | 3-4 internal grade | Industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	0	0
Year two, originated in prior fiscal year one	0	0
Year three, originated in prior fiscal year two	0	56,933
Year four, originated in prior fiscal year three	0	0
Year five, original in prior fiscal year four	0	0
Year six, originated in prior fiscal year five	0
Total	0	56,933
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | 3-4 internal grade | Mixed Use
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	0	0
Year two, originated in prior fiscal year one	0	0
Year three, originated in prior fiscal year two	0	0
Year four, originated in prior fiscal year three	0	0
Year five, original in prior fiscal year four	0	0
Year six, originated in prior fiscal year five	0
Total	0	0
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | 3-4 internal grade | Hospitality
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	0	0
Year two, originated in prior fiscal year one	0	0
Year three, originated in prior fiscal year two	0	113,961
Year four, originated in prior fiscal year three	29,966	52,790
Year five, original in prior fiscal year four	0	79,102
Year six, originated in prior fiscal year five	78,928
Total	108,894	245,853
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | 3-4 internal grade | Self Storage
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	0	0
Year two, originated in prior fiscal year one	0	0
Year three, originated in prior fiscal year two	0	0
Year four, originated in prior fiscal year three	0	0
Year five, original in prior fiscal year four	0	0
Year six, originated in prior fiscal year five	0
Total	0	0
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | 3-4 internal grade | Manufactured Housing
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	0	0
Year two, originated in prior fiscal year one	0	0
Year three, originated in prior fiscal year two	0	0
Year four, originated in prior fiscal year three	0	0
Year five, original in prior fiscal year four	0	0
Year six, originated in prior fiscal year five	0
Total	0	$ 0
Commercial Portfolio Segment | Commercial Mortgage Receivable, Held-For-Investment | 5 internal grade | Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Year one, originated in current fiscal year	105,498
Year two, originated in prior fiscal year one	0
Year three, originated in prior fiscal year two	0
Year four, originated in prior fiscal year three	0
Year five, original in prior fiscal year four	0
Year six, originated in prior fiscal year five	0
Total	$ 105,498