Series A Convertible Preferred Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended	9 Months Ended
	Jul. 01, 2019	Apr. 04, 2019	Sep. 30, 2019	Sep. 30, 2019
Series A Convertible Preferred Stock [Member]
Class Of Stock [Line Items]
Convertible preferred stock liquidation preference		100.00%
Discounted rate of remaining scheduled dvidends		10.00%
Carlyle [Member]
Class Of Stock [Line Items]
Agreement date		Nov. 08, 2018
Carlyle [Member] | Series A Convertible Preferred Stock [Member]
Class Of Stock [Line Items]
Convertible preferred stock, share issued		1,000,000
Total purchase price		$ 1,000.0
Total purchase price per share		$ 1,000
Direct and incremental expenses incurred				$ 3.0
Convertible preferred stock, conversion price per share		$ 27.50
Initial conversion rate of common stock per share of the convertible preferred stock		36.3636
Convertible preferred stock, conversion price per share		$ 49.50
Convertible preferred stock threshold trading days		30 days
Convertible preferred stock threshold consecutive trading days		45 days
Convertible preferred stock threshold final trading days of consecutive trading days		5 days
Carlyle [Member] | Series A Convertible Preferred Stock [Member]
Class Of Stock [Line Items]
Liquidation perference per share		$ 1,000
Convertible preferred stock, dividend payment terms				Holders of the Convertible Preferred Stock are entitled to a cumulative dividend at the rate of 5.5% per year, payable quarterly in arrears.
Convertible preferred stock, dividend rate percentage		5.50%
Increase in convertible preferred stock dividend rate percentage				2.50%
Convertible preferred stock, dividend rate if dividend not paid				8.00%
Additional increase in convertible preferred stock dividend rate percentage quaterly.				0.50%
Convertible preferred stock dividend rate percentage subject to a cap per year				11.00%
Dividends declared payable in cash			$ 13.8	$ 26.9
Dividends paid date	Sep. 30, 2019
ARRIS [Member]
Class Of Stock [Line Items]
Convertible preferred stock, share issued		2,100,000
Total purchase price		$ 7,700.0
Business acquisition, percentage of common stock issuable capped at common stock outstanding		19.90%