Assets - Available-For-Sale Securities (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2019	Sep. 30, 2020	Dec. 31, 2019
Total available-for-sale securities
Amortized Cost		$ 161,568	$ 115,219
Gross Unrealized Gains		30	38
Gross Unrealized Losses		(13)	(5)
Estimated Fair Value		161,585	115,252
Available-for-sale securities in a loss position
Estimated Fair Value		56,301	28,945
Gross Unrealized Losses		(13)	(5)
Investments that had been in a continuous loss position for more than 12 months		0	0
Realized gains or losses
Realized gains	$ 0
Realized losses	$ 0
U.S. treasuries
Total available-for-sale securities
Amortized Cost		125,333	105,096
Gross Unrealized Gains		17	38
Gross Unrealized Losses		(4)	(4)
Estimated Fair Value		125,346	105,130
Available-for-sale securities in a loss position
Estimated Fair Value		40,111	22,943
Gross Unrealized Losses		(4)	(4)
Government agency securities
Total available-for-sale securities
Amortized Cost		5,995	1,139
Gross Unrealized Gains		5
Estimated Fair Value		6,000	1,139
Corporate debt
Total available-for-sale securities
Amortized Cost		14,254	6,003
Gross Unrealized Gains		1
Gross Unrealized Losses		(7)	(1)
Estimated Fair Value		14,248	6,002
Available-for-sale securities in a loss position
Estimated Fair Value		10,195	6,002
Gross Unrealized Losses		(7)	(1)
Commercial paper
Total available-for-sale securities
Amortized Cost		15,986	2,981
Gross Unrealized Gains		7
Gross Unrealized Losses		(2)
Estimated Fair Value		15,991	$ 2,981
Available-for-sale securities in a loss position
Estimated Fair Value		5,995
Gross Unrealized Losses		$ (2)

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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