Significant Accounting Policies - Investment in Marketable Securities (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2022 USD ($) security	Jun. 30, 2021 USD ($) security	Jun. 30, 2022 USD ($) security	Jun. 30, 2021 USD ($) security	Dec. 31, 2021 USD ($) security
Investment in Marketable Securities
Total marketable securities available-for-sale	$ 21,899,000		$ 21,899,000		$ 24,146,000
Total investment in marketable securities	26,260,000		26,260,000		34,752,000
Marketable securities, unrealized loss	6,200,000	$ 1,900,000	6,200,000	$ 1,900,000
Proceeds from sale of marketable securities	0	$ 0	0	$ 5,000,000
Number of marketable securities sold | security		1		1
Fair Value
Investment in Marketable Securities
Total marketable securities available-for-sale	21,899,000		21,899,000		24,146,000
Total investment in marketable securities	26,260,000		26,260,000		34,752,000
Commercial mortgage-backed securities
Investment in Marketable Securities
Total marketable securities available-for-sale	21,899,000		21,899,000		24,146,000
Cost basis of commercial mortgage-backed securities	$ 23,000,000		$ 23,000,000		$ 23,000,000
Number of securities in continuous unrealized loss position | security	1		1		1
Unrealized loss			$ 2,100,000		$ 600,000
Fair value of security in a continuous unrealized loss position for less than 12 months	$ 5,600,000		5,600,000		7,200,000
Equity marketable securities
Investment in Marketable Securities
Total investment in marketable securities	$ 4,361,000		$ 4,361,000		$ 10,606,000