Repurchases of ARRIS Shares - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions	1 Months Ended	3 Months Ended		6 Months Ended	12 Months Ended
	Aug. 01, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity, Class of Treasury Stock [Line Items]
Shares repurchased		4.0	1.0
Average price per share		$ 25.29	$ 25.35
Shares repurchased, value		$ 99,900,000	$ 25,000,000
Maximum period of shareholders approval				5 years
Remaining authorized amount for stock repurchases		$ 400,100,000		$ 400,100,000
Subsequent Event
Equity, Class of Treasury Stock [Line Items]
Shares repurchased	2.0
Shares repurchased, value	$ 50,000,000
Remaining authorized amount for stock repurchases	$ 350,000,000
Maximum
Equity, Class of Treasury Stock [Line Items]
Share repurchase plans, authorized amount			$ 300,000,000			$ 300,000,000	$ 300,000,000
Minimum | Scenario Forecast
Equity, Class of Treasury Stock [Line Items]
Shares repurchased, value					$ 400,000,000