Marketable Securities - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Sep. 30, 2020
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Adjusted Cost	$ 53,238	$ 147,056
Unrealized Gains	1,151	1,499
Unrealized Losses	(5)	(88)
Fair Value	54,384	148,467
Equity securities
Debt Securities, Trading, and Equity Securities, FV-NI [Abstract]
Adjusted Cost	4,234
Unrealized Gains	170
Unrealized Losses	0
Fair Value	4,404
Money market and mutual funds
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Adjusted Cost	38,028	103,204
Unrealized Gains	771	1,041
Unrealized Losses	0	(59)
Fair Value	38,799	104,186
Corporate bonds
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Adjusted Cost	4,021	20,212
Unrealized Gains	77	227
Unrealized Losses	0	(24)
Fair Value	4,098	20,415
Government securities - U.S.
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Adjusted Cost	5,341	20,015
Unrealized Gains	110	202
Unrealized Losses	(5)	(1)
Fair Value	5,446	20,216
Other fixed-income securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Adjusted Cost	1,614	3,625
Unrealized Gains	23	29
Unrealized Losses	0	(4)
Fair Value	$ 1,637	$ 3,650

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) 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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