Employee Benefit Plans - Change in Obligation (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at the beginning of the year	$ 61.0	$ 50.4
Additions due to acquisition of Microsemi	9.8	0.0
Service costs	1.5	2.2	$ 1.4
Interest costs	1.1	1.0	1.0
Actuarial losses	6.0	0.7
Benefits paid	(0.9)	(0.8)
Foreign currency exchange rate changes	(5.8)	7.5
Projected benefit obligation at the end of the year	72.7	61.0	$ 50.4
Accumulated benefit obligation at the end of the year	$ 66.7	$ 55.5
Weighted average assumed discount rate	1.41%	1.73%
Weighted average assumed compensation rate of increase	2.79%	2.91%
Defined benefit pension plan, liabilities	$ 72.7	$ 61.0
Defined benefit pension plan liabilities, current	1.3	0.9
Defined benefit pension plan, liabilities, noncurrent	$ 71.4	$ 60.1