Significant Accounting Policies - Investment in Marketable Securities (Details) $ in Thousands	12 Months Ended
Dec. 31, 2020 USD ($) security	Dec. 31, 2019 USD ($)
Investment in Marketable Securities
Marketable Securities	$ 28,570	$ 29,887
Fair Value
Investment in Marketable Securities
Marketable Securities	28,570	29,887
Commercial mortgage-backed securities
Investment in Marketable Securities
Marketable Securities	28,570	29,887
Cost basis of commercial mortgage backed securities	$ 27,500	27,500
Number of securities in continuous unrealized loss position \| security	1
Unrealized loss	$ 700
Fair value of security in a continuous unrealized loss position for less than 12 months	7,000
Equity marketable securities
Investment in Marketable Securities
Cost basis of commercial mortgage backed securities	$ 0	$ 0

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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