Summary of Significant Accounting Policies - Investments by Maturity Date (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Amortized Cost
2021	$ 140,950
2022	2,611
Amortized Cost	143,561	$ 101,599
Estimated Fair Value
2021	140,847
2022	2,612
Estimated Fair Value	$ 143,459	$ 101,661	$ 98,878

Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year Two

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Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year Two

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

+ References

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