Joint Ventures and Investments - Cost Method Investments (Parenthetical) (Detail) - Complex Media - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jul. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Jul. 31, 2017
Schedule Of Investments [Line Items]
Cash received in connection with sale of interest	$ 35,300			$ 2,728	$ 35,284
Additional amount held in escrow	$ 3,700					$ 3,700
Period for amount held in escrow	12 months
Period following the closing date for escrow account	18 months
Gain on sale of investments		$ 2,700	$ 10,200	$ 2,728	$ 10,164
Cash received from escrow						$ 2,700