Goodwill and Intangible Assets, Net - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite Lived Intangible Assets [Line Items]
Weighted-average remaining useful lives of acquired intangible assets	4 years 1 month 6 days
Impairment charges		$ 20,700
Trademarks, Branding and Domain Names [Member]
Finite Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	$ 6,100,000	6,100,000
Weighted-average remaining useful lives of acquired intangible assets	7 years
Developed Technology [Member]
Finite Lived Intangible Assets [Line Items]
Weighted-average remaining useful lives of acquired intangible assets	4 years 3 months 18 days
Acquired Lease Intangibles [Member]
Finite Lived Intangible Assets [Line Items]
Weighted-average remaining useful lives of acquired intangible assets	2 years 3 months 18 days
Other Intangible Assets [Member]
Finite Lived Intangible Assets [Line Items]
Amortization expense	$ 16,200,000	$ 29,000,000	$ 27,400,000
Noncompetition Agreements [Member]
Finite Lived Intangible Assets [Line Items]
Weighted-average remaining useful lives of acquired intangible assets	1 year 6 months