Marketable Securities - Proceeds From Maturities of Available-For-Sale Securities (Details) - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Proceeds from marketable securities	$ 34,728,000	$ 43,762,000	$ 16,367,000
Sales of marketable securities	1,464,000	0	0
Total	36,192,000	43,762,000	16,367,000
Gross realized gain related to the sale of marketable securities	$ 35,000	$ 0	$ 0

Amount of realized gain (loss) on 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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Amount of cash inflow from maturity, prepayment and call 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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Amount of cash inflow from sale, maturity, prepayment and call of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amount of cash inflow from sale 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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