Short-Term and Long-Term Investments - Schedule of Investments That Have Been in a Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Fair Value
Less than 12 months	$ 88,883	$ 85,304
12 months or greater	0	5,006
Total	88,883	90,310
Gross Unrealized Losses
Less than 12 months	(10)	(31)
12 months or greater	0	(1)
Total	(10)	(32)
Corporate Bonds and Notes
Fair Value
Less than 12 months	26,703	43,492
12 months or greater	0	5,006
Total	26,703	48,498
Gross Unrealized Losses
Less than 12 months	(5)	(28)
12 months or greater	0	(1)
Total	(5)	(29)
U.S. Government Securities
Fair Value
Less than 12 months	29,053	41,812
12 months or greater	0	0
Total	29,053	41,812
Gross Unrealized Losses
Less than 12 months	(4)	(3)
12 months or greater	0	0
Total	(4)	$ (3)
U.S. Government Agency Securities
Fair Value
Less than 12 months	33,127
12 months or greater	0
Total	33,127
Gross Unrealized Losses
Less than 12 months	(1)
12 months or greater	0
Total	$ (1)