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v3.21.2

Significant Accounting Policies - Investment in Marketable Securities (Details) | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2021 USD ($) security | Sep. 30, 2020 USD ($) | Sep. 30, 2021 USD ($) security | Sep. 30, 2020 USD ($) | Dec. 31, 2020 USD ($)
Investment in Marketable Securities |  |  |  |  |
Marketable securities available-for-sale | $ 24,355,000 |  | $ 24,355,000 |  | $ 28,570,000
Equity marketable securities | 34,428,000 |  | 34,428,000 |  | 28,570,000
Marketable securities, unrealized gain | 2,000,000 |  | 100,000 |  |
Proceeds from sale of marketable securities | 0 | $ 0 | $ 4,500,000 | $ 0 |
Number of marketable securities sold | security |  |  | 1 |  |
Fair Value |  |  |  |  |
Investment in Marketable Securities |  |  |  |  |
Marketable securities available-for-sale | 24,355,000 |  | $ 24,355,000 |  | 28,570,000
Equity marketable securities | 34,428,000 |  | 34,428,000 |  | 28,570,000
Commercial mortgage-backed securities |  |  |  |  |
Investment in Marketable Securities |  |  |  |  |
Marketable securities available-for-sale | 24,355,000 |  | 24,355,000 |  | 28,570,000
Cost basis of commercial mortgage-backed securities | $ 23,000,000 |  | $ 23,000,000 |  | 27,500,000
Number of securities in continuous unrealized loss position | security | 1 |  | 1 |  |
Unrealized loss |  |  | $ 500,000 |  | 700,000
Fair value of security in a continuous unrealized loss position for less than 12 months | $ 7,200,000 |  | 7,200,000 |  | 7,000,000
Equity Securities |  |  |  |  |
Investment in Marketable Securities |  |  |  |  |
Equity marketable securities | $ 10,073,000 |  | $ 10,073,000 |  | $ 0

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