Purchases of ARRIS Shares (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2018	Mar. 31, 2018
Equity, Class of Treasury Stock [Line Items]
Shares repurchased	4,000,000	1,000,000
Shares repurchased, value	$ 99.9	$ 25.0
Repurchased to satisfy tax withholding obligations on vesting shares
Equity, Class of Treasury Stock [Line Items]
Shares subject to equity awards cancelled for cash to satisfy minimum tax withholding obligations	128
Stock Repurchased Pending Settlement
Equity, Class of Treasury Stock [Line Items]
Shares repurchased	557,715
Shares repurchased, value	$ 13.7