Commercial Mortgage Loans - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			$ 921
Increase/(decrease) in provision for credit losses	$ (3,710)	$ (245)	14,929	$ 2,823
Ending Balance	22,777		22,777
Commercial Portfolio Segment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	26,244		921
Increase/(decrease) in provision for credit losses	(3,467)		15,072
Write offs			(427)
Ending Balance	22,777		22,777
Commercial Portfolio Segment | Multifamily
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	10,742		322
Increase/(decrease) in provision for credit losses	(3,937)		3,263
Write offs			0
Ending Balance	6,805		6,805
Commercial Portfolio Segment | Retail
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	780		202
Increase/(decrease) in provision for credit losses	(327)		(135)
Write offs			0
Ending Balance	453		453
Commercial Portfolio Segment | Office
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	4,350		249
Increase/(decrease) in provision for credit losses	(2,336)		(201)
Write offs			0
Ending Balance	2,014		2,014
Commercial Portfolio Segment | Industrial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	599		23
Increase/(decrease) in provision for credit losses	170		312
Write offs			0
Ending Balance	769		769
Commercial Portfolio Segment | Mixed Use
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	2,250		4
Increase/(decrease) in provision for credit losses	(1,003)		1,234
Write offs			0
Ending Balance	1,247		1,247
Commercial Portfolio Segment | Hotel
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	7,243		103
Increase/(decrease) in provision for credit losses	4,024		10,852
Write offs			(427)
Ending Balance	11,267		11,267
Commercial Portfolio Segment | Self Storage
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	220		0
Increase/(decrease) in provision for credit losses	(92)		(271)
Write offs			0
Ending Balance	128		128
Commercial Portfolio Segment | Manufactured Housing
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	60		18
Increase/(decrease) in provision for credit losses	34		18
Write offs			0
Ending Balance	94		94
Unfunded Loan Commitment | Commercial Portfolio Segment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	650		0
Increase/(decrease) in provision for credit losses	(243)		(143)
Ending Balance	407		407
Unfunded Loan Commitment | Commercial Portfolio Segment | Multifamily
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	225		0
Increase/(decrease) in provision for credit losses	(111)		(125)
Ending Balance	114		114
Unfunded Loan Commitment | Commercial Portfolio Segment | Retail
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	0		0
Increase/(decrease) in provision for credit losses	0		(40)
Ending Balance	0		0
Unfunded Loan Commitment | Commercial Portfolio Segment | Office
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	149		0
Increase/(decrease) in provision for credit losses	(73)		(74)
Ending Balance	76		76
Unfunded Loan Commitment | Commercial Portfolio Segment | Industrial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	40		0
Increase/(decrease) in provision for credit losses	144		154
Ending Balance	184		184
Unfunded Loan Commitment | Commercial Portfolio Segment | Mixed Use
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	0		0
Increase/(decrease) in provision for credit losses	0		(1)
Ending Balance	0		0
Unfunded Loan Commitment | Commercial Portfolio Segment | Hotel
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	235		0
Increase/(decrease) in provision for credit losses	(203)		(25)
Ending Balance	32		32
Unfunded Loan Commitment | Commercial Portfolio Segment | Self Storage
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	0		0
Increase/(decrease) in provision for credit losses	0		(28)
Ending Balance	0		0
Unfunded Loan Commitment | Commercial Portfolio Segment | Manufactured Housing
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	1		0
Increase/(decrease) in provision for credit losses	0		(4)
Ending Balance	$ 1		1
Transition Adjustment | Commercial Portfolio Segment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			7,211
Transition Adjustment | Commercial Portfolio Segment | Multifamily
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			3,220
Transition Adjustment | Commercial Portfolio Segment | Retail
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			386
Transition Adjustment | Commercial Portfolio Segment | Office
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			1,966
Transition Adjustment | Commercial Portfolio Segment | Industrial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			434
Transition Adjustment | Commercial Portfolio Segment | Mixed Use
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			9
Transition Adjustment | Commercial Portfolio Segment | Hotel
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			739
Transition Adjustment | Commercial Portfolio Segment | Self Storage
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			399
Transition Adjustment | Commercial Portfolio Segment | Manufactured Housing
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			58
Transition Adjustment | Unfunded Loan Commitment | Commercial Portfolio Segment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			550
Transition Adjustment | Unfunded Loan Commitment | Commercial Portfolio Segment | Multifamily
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			239
Transition Adjustment | Unfunded Loan Commitment | Commercial Portfolio Segment | Retail
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			40
Transition Adjustment | Unfunded Loan Commitment | Commercial Portfolio Segment | Office
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			150
Transition Adjustment | Unfunded Loan Commitment | Commercial Portfolio Segment | Industrial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			30
Transition Adjustment | Unfunded Loan Commitment | Commercial Portfolio Segment | Mixed Use
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			1
Transition Adjustment | Unfunded Loan Commitment | Commercial Portfolio Segment | Hotel
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			57
Transition Adjustment | Unfunded Loan Commitment | Commercial Portfolio Segment | Self Storage
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			28
Transition Adjustment | Unfunded Loan Commitment | Commercial Portfolio Segment | Manufactured Housing
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance			$ 5