Joint Ventures and Investments - Cost Method Investments (Parenthetical) (Detail) - Complex Media - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Jul. 31, 2016	Sep. 30, 2016	Jul. 31, 2017
Schedule Of Investments [Line Items]
Cash received in connection with sale of interest	$ 35.3
Additional amount held in escrow	$ 3.7
Period for amount held in escrow	12 months
Period following the closing date for escrow account	18 months
Gain on sale of investments		$ 10.2
Subsequent Event
Schedule Of Investments [Line Items]
Additional amount held in escrow			$ 3.7
Cash received from escrow			$ 2.7