Joint Venture - Additional Information (Details) - USD ($)	3 Months Ended		12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Jan. 31, 2019
Schedule Of Equity Method Investments [Line Items]
Accumulated deficit	$ (481,311,000)		$ (481,713,000)
Goodwill	$ 57,834,000		57,717,000	$ 57,770,000
Impairment of goodwill			0
Accuray Asia
Schedule Of Equity Method Investments [Line Items]
Percentage of ownership interest in joint venture	49.00%				49.00%
Gain on contribution to joint venture		$ 13,000,000.0
Non cash revenue recognized from joint venture	$ 1,400,000
Joint venture associated costs	200,000
Deferred of intra-entity profit margin	1,500,000		$ 1,800,000
Previously deferred intra-entity margin from system sales	1,000,000.0
Deferral of intra entity margin from system sales	700,000
Accumulated deficit	200,000
Equity method investment	15,600,000
Proportional share of underlying equity in net assets	12,300,000
Equity method investment, intra-entity profit	1,500,000
Difference in equity method investment	3,300,000
Elimination of equity method investment intra-entity profit on sales	1,500,000
Goodwill	4,800,000
Impairment of goodwill	$ 0