Intangible Assets - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Amortization of website development costs and intangible assets included in technology and development	$ 94,349	$ 87,060	$ 63,189
Non-cash impairment of indefinite-lived intangible assets	174,000		19,001
Trulia
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible asset	177,000	351,000
Non-cash impairment of indefinite-lived intangible assets	174,000
Technology and Development
Finite-Lived Intangible Assets [Line Items]
Amortization of website development costs and intangible assets included in technology and development	$ 54,300	$ 47,000	$ 39,300