Commercial Mortgage Loans - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance		$ 40,848		$ 40,848
Provision/(benefit) for credit losses	$ 21,624		$ 32,530	25,984	$ 31,575
Ending balance	38,932			38,932
General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance		26,624		26,624
Ending balance	38,932			38,932
Specific allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance		14,224		14,224
Ending balance	0			0
Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	28,751	40,848		40,848
Ending balance	38,932	28,751		38,932
Commercial Portfolio Segment | General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	10,181	2,127		12,300
Commercial Portfolio Segment | Specific allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	11,893	835
Write offs against specific allowance for credit losses	(11,893)	(15,059)
Commercial Portfolio Segment | Unfunded Loan Commitment
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,678	280		280
Ending balance	1,228	1,678		1,228
Commercial Portfolio Segment | Unfunded Loan Commitment | General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	(450)	1,398
Commercial Portfolio Segment | Multifamily
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	19,407	21,166		21,166
Ending balance	29,735	19,407		29,735
Commercial Portfolio Segment | Multifamily | General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	10,328	(1,759)
Commercial Portfolio Segment | Multifamily | Specific allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	0	0
Write offs against specific allowance for credit losses	0	0
Commercial Portfolio Segment | Multifamily | Unfunded Loan Commitment
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	744	165		165
Ending balance	1,096	744		1,096
Commercial Portfolio Segment | Multifamily | Unfunded Loan Commitment | General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	352	579
Commercial Portfolio Segment | Retail
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	34	14,601		14,601
Ending balance	303	34		303
Commercial Portfolio Segment | Retail | General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	269	(343)
Commercial Portfolio Segment | Retail | Specific allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	0	835
Write offs against specific allowance for credit losses	0	(15,059)		(15,100)
Commercial Portfolio Segment | Retail | Unfunded Loan Commitment
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	0	(36)		(36)
Ending balance	2	0		2
Commercial Portfolio Segment | Retail | Unfunded Loan Commitment | General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	2	36
Commercial Portfolio Segment | Office
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	3,656	670		670
Ending balance	877	3,656		877
Commercial Portfolio Segment | Office | General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	(2,779)	2,986
Commercial Portfolio Segment | Office | Specific allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	11,893	0
Write offs against specific allowance for credit losses	(11,893)	0
Commercial Portfolio Segment | Office | Unfunded Loan Commitment
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	890	86		86
Ending balance	64	890		64
Commercial Portfolio Segment | Office | Unfunded Loan Commitment | General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	(826)	804
Commercial Portfolio Segment | Industrial
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	54	259		259
Ending balance	64	54		64
Commercial Portfolio Segment | Industrial | General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	10	(205)
Commercial Portfolio Segment | Industrial | Specific allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	0	0
Write offs against specific allowance for credit losses	0	0
Commercial Portfolio Segment | Industrial | Unfunded Loan Commitment
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	3	3		3
Ending balance	3	3		3
Commercial Portfolio Segment | Industrial | Unfunded Loan Commitment | General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	0	0
Commercial Portfolio Segment | Mixed Use
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	77	47		47
Ending balance	77	77		77
Commercial Portfolio Segment | Mixed Use | General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	0	30
Commercial Portfolio Segment | Mixed Use | Specific allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	0	0
Write offs against specific allowance for credit losses	0	0
Commercial Portfolio Segment | Mixed Use | Unfunded Loan Commitment
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	0	0		0
Ending balance	0	0		0
Commercial Portfolio Segment | Mixed Use | Unfunded Loan Commitment | General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	0	0
Commercial Portfolio Segment | Hospitality
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	5,406	4,064		4,064
Ending balance	7,727	5,406		7,727
Commercial Portfolio Segment | Hospitality | General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	2,321	1,342
Commercial Portfolio Segment | Hospitality | Specific allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	0	0
Write offs against specific allowance for credit losses	0	0
Commercial Portfolio Segment | Hospitality | Unfunded Loan Commitment
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	40	61		61
Ending balance	63	40		63
Commercial Portfolio Segment | Hospitality | Unfunded Loan Commitment | General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	23	(21)
Commercial Portfolio Segment | Self Storage
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	55	10		10
Ending balance	44	55		44
Commercial Portfolio Segment | Self Storage | General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	(11)	45
Commercial Portfolio Segment | Self Storage | Specific allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	0	0
Write offs against specific allowance for credit losses	0	0
Commercial Portfolio Segment | Self Storage | Unfunded Loan Commitment
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	0	0		0
Ending balance	0	0		0
Commercial Portfolio Segment | Self Storage | Unfunded Loan Commitment | General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	0	0
Commercial Portfolio Segment | Manufactured Housing
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	62	31		31
Ending balance	105	62		105
Commercial Portfolio Segment | Manufactured Housing | General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	43	31
Commercial Portfolio Segment | Manufactured Housing | Specific allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	0	0
Write offs against specific allowance for credit losses	0	0
Commercial Portfolio Segment | Manufactured Housing | Unfunded Loan Commitment
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Beginning balance	1	1		1
Ending balance	0	1		$ 0
Commercial Portfolio Segment | Manufactured Housing | Unfunded Loan Commitment | General allowance/(benefit) for credit losses
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision/(benefit) for credit losses	$ (1)	$ 0