Net Income Per Common Share Attributable to Alpha and Omega Semiconductor Limited - Potential Dilutive Shares (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities (in shares)	2,665	3,116	2,825	3,208
Employee stock options and RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities (in shares)	2,038	2,225	2,043	2,220
ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities (in shares)	627	891	782	988