Joint Venture - Additional Information (Details) - USD ($)	3 Months Ended			12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2019	Jan. 31, 2019
Schedule Of Equity Method Investments [Line Items]
Accumulated deficit	$ 488,203,000				$ 488,024,000
Investee's currency translation adjustment	(9,000)			$ 243,000
Goodwill	$ 57,951,000			$ 57,960,000	57,960,000	$ 57,717,000
Impairment of goodwill		$ 0
Accuray Asia
Schedule Of Equity Method Investments [Line Items]
Percentage of ownership interest in joint venture	49.00%						49.00%
Deferred of intra-entity profit margin	$ 3,900,000				$ 2,100,000
Previously deferred intra-entity margin from system sales	200,000		$ 1,000,000.0
Deferral of intra entity margin from system sales	1,900,000		$ 700,000
Accumulated deficit	400,000
Equity method investment	14,700,000
Proportional share of underlying equity in net assets	13,900,000
Investee's currency translation adjustment	900,000
Elimination of equity method investment intra-entity profit on sales	3,900,000
Proportional share of underlying equity in net assets, difference amount	800,000
Goodwill	4,700,000
Impairment of goodwill	$ 0