Net Income per Share - Schedule of Computation of Net Income per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 24, 2021	Dec. 25, 2020	Dec. 24, 2021	Dec. 25, 2020
Earnings Per Share [Abstract]
Net income attributable to Allegro MicroSystems, Inc.	$ 32,936	$ (5,095)	$ 93,791	$ 9,309
Net (loss) income attributable to common stockholders, basic	32,973	(5,060)	93,903	9,412
Net (loss) income attributable to common stockholders, diluted	$ 32,973	$ (5,060)	$ 93,903	$ 9,412
Basic weighted average shares of common stock (in shares)	189,736,901	124,363,078	189,665,324	48,121,026
Dilutive effect of common stock equivalents (in shares)	2,331,321	0	2,013,627	123,517,761
Diluted weighted average common shares (in shares)	192,068,222	124,363,078	191,678,951	171,638,787
Basic net income attributable to Allegro MicroSystems, Inc. per share (in dollars per share)	$ 0.17	$ (0.04)	$ 0.49	$ 0.19
Basic net income attributable to common stockholders per share (in dollars per share)	0.17	(0.04)	0.50	0.20
Diluted net income attributable to Allegro MicroSystems, Inc. per share (in dollars per share)	0.17	(0.04)	0.49	0.05
Diluted net income attributable to common stockholders per share (in dollars per share)	$ 0.17	$ (0.04)	$ 0.49	$ 0.05