Short-Term Debt - Mortgage Loan Participation and Sale Agreement (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021	Jul. 30, 2021
Carrying value:
Mortgage loan participation and sale agreement secured by mortgage loan participation certificates	$ 502,116,000		$ 502,116,000		$ 479,845,000
Fair value of loans pledged to secure	532,175,000		532,175,000		505,716,000
Mortgage Loan Participation and Sale Agreement member
During the period:
Average balance	$ 214,654,000	$ 254,343,000	$ 218,977,000	$ 265,390,000
Weighted-average interest rate (as a percent)	2.25%	1.36%	1.98%	1.35%
Total interest expense	$ 1,377,000	$ 1,039,000	$ 2,497,000	$ 2,134,000
Carrying value:
Unpaid principal balance of mortgage loan participation and sale agreement secured by mortgage loan participation certificates	502,775,000		502,775,000		479,845,000
Unamortized debt issuance costs	(659,000)		(659,000)
Mortgage loan participation and sale agreement secured by mortgage loan participation certificates	$ 502,116,000		$ 502,116,000		$ 479,845,000
Weighted average interest rate (as a percent)	2.85%		2.85%		1.48%
Fair value of loans pledged to secure	$ 532,175,000		$ 532,175,000		$ 505,716,000
Amortization of debt issuance costs	172,000	172,000	344,000	344,000
Mortgage Loan Participation and Sale Agreement member | Maximum
Carrying value:
Mortgage loan participation and sale agreement secured by mortgage loan participation certificates	514,054,000	528,844,000	515,043,000	528,844,000
Note Payable
Carrying value:
Unamortized debt issuance costs	(6,740,000)		(6,740,000)		$ (2,378,000)
Amortization of debt issuance costs	$ 548,000	$ 634,000	$ 1,000,000.0	$ 1,200,000
Syndicated Repurchase Agreement
Short-term Debt [Line Items]
Previous maximum aggregate purchase price						$ 400,000,000
Maximum aggregate purchase price						500,000,000
Syndicated Repurchase Agreement SAR
Short-term Debt [Line Items]
Maximum aggregate purchase price						$ 600,000,000