Significant Accounting Policies - Investment in Marketable Securities (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($) security	Dec. 31, 2022 USD ($)
Investment in Marketable Securities
Commercial mortgage-backed securities	$ 9,616,000		$ 9,616,000		$ 11,240,000
Total investment in marketable securities	9,616,000		9,616,000		11,240,000
Proceeds from sale of marketable securities	0	$ 7,800,000	0	$ 7,800,000
Number of marketable securities sold | security				1
Proceeds from repayment of debt marketable securities		3,700,000		$ 3,700,000
Number of securities repaid | security				1
Equity marketable securities	0		0		0
Marketable securities, unrealized loss		$ 100,000		$ 6,100,000
Commercial mortgage-backed securities
Investment in Marketable Securities
Commercial mortgage-backed securities	9,616,000		9,616,000		11,240,000
Cost basis of commercial mortgage-backed securities	11,500,000		11,500,000		11,500,000
Unrealized loss			1,900,000		300,000
Fair value of security in a continuous unrealized loss position for less than 12 months	$ 9,600,000		$ 9,600,000		$ 11,200,000