Mortgage Loans - Allowance for loan losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning of period	$ (5,985)	$ (9,126)	$ (6,107)	$ (7,112)
Reclassification (from)/to non-credit discount (to)/from the allowance for changes in payment timing expectations	(1,207)	2,304	(4,206)	(4,488)
Decrease/(increase) in allowance for expected credit losses for loan acquisitions during the period	152	(253)	(100)	(281)
Credit loss expense on mortgage loans	(76)	(80)	(190)	(307)
(Increase in)/reversal of allowance for expected credit losses due (increases)/decreases in the net present value of expected cash flows	(330)	1,935	3,157	6,968
Allowance for expected credit losses, end of period	$ (7,446)	$ (5,220)	$ (7,446)	$ (5,220)