CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)		3 Months Ended		12 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2019
Cash flows from operating activities:
Net income		$ 50,700,000	$ 35,700,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		307,100,000	172,800,000
Deferred income taxes		(16,800,000)	87,200,000
Share-based compensation expense related to equity incentive plans		40,700,000	45,300,000
Loss on settlement of debt		1,900,000	0
Amortization of debt discount		29,900,000	27,700,000
Amortization of debt issuance costs		4,200,000	2,800,000
Losses on equity method investments		0	100,000
Impairment of intangible assets		500,000	2,000,000.0
(Gains) losses on available-for-sale investments and marketable equity securities, net		(800,000)	5,200,000
Amortization of premium on available-for-sale investments		0	(200,000)
Other non-cash adjustment		(100,000)	(100,000)
Changes in operating assets and liabilities, excluding impact of acquisitions:
Increase in accounts receivable		(56,200,000)	(55,200,000)
(Increase) decrease in inventories		(20,500,000)	83,800,000
Increase (decrease) in accounts payable and accrued liabilities		49,700,000	(2,200,000)
Change in other assets and liabilities		14,400,000	(88,600,000)
Change in income tax payable		(24,100,000)	(13,900,000)
Net cash provided by operating activities		380,600,000	302,400,000
Cash flows from investing activities:
Purchases of available-for-sale investments		0	(167,700,000)
Maturities of available-for-sale investments		0	66,700,000
Sales of available-for-sale investments		0	1,376,600,000	$ 1,380,000,000
Acquisition of Microsemi, net of cash acquired		0	(7,851,200,000)
Investments in other assets		(2,600,000)	(1,600,000)
Proceeds from sale of assets		200,000	100,000
Capital expenditures		(23,900,000)	(89,400,000)
Net cash used in investing activities		(26,300,000)	(6,666,500,000)
Cash flows from financing activities:
Proceeds from issuance of 2023 and 2021 Senior Notes		0	1,989,500,000
Repayment of debt assumed in Microsemi acquisition		0	(2,056,900,000)
Deferred financing costs		0	(72,600,000)
Payment of cash dividends		(87,100,000)	(85,500,000)
Proceeds from sale of common stock		7,300,000	6,400,000
Tax payments related to shares withheld for vested restricted stock units		(11,400,000)	(16,800,000)
Capital lease payments		(200,000)	(100,000)
Net cash (used in) provided by financing activities		(348,900,000)	6,098,000,000.0
Net increase (decrease) in cash and cash equivalents		5,400,000	(266,100,000)
Cash and cash equivalents, and restricted cash at beginning of period	[1]	428,600,000	901,300,000	901,300,000
Cash and cash equivalents, and restricted cash at end of period	[1]	434,000,000.0	635,200,000	428,600,000
Restricted cash		38,800,000		38,400,000
Supplemental Cash Flow Information [Abstract]
Right-of-use assets obtained in exchange of lease liabilities		0
Operating lease payments in operating cash flows		(14,800,000)
Term Loan Facility
Cash flows from financing activities:
Proceeds from borrowings under credit facility		0	3,000,000,000.0	$ 500,000,000.0
Repayments of credit facility		(188,000,000.0)	0
Revolving Credit Facility
Cash flows from financing activities:
Proceeds from borrowings under credit facility		204,000,000.0	3,485,500,000
Repayments of credit facility		$ (273,500,000)	$ (151,500,000)

[1] Schedule of restricted cash
The following table presents the balance of restricted cash which consists of cash denominated in a foreign currency and restricted in use due to a foreign taxing authority requirement (in millions):
  June 30,   March 31,   2019   2019 Restricted cash $ 38.8
  $ 38.4