Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 28, 2015
Schedule Of Income Tax [Line Items]
Income tax (benefit) expense	$ 31,102	$ 89,586	$ (130)
Effective tax rate	20.70%	48.70%	(0.10%)
Adjustment to income tax (benefit) under the Tax Act	$ (5,900)
Non-cash impairment of indefinite-lived intangible assets	79,000	$ 174,000	$ 0
Income tax benefit, Tax Cuts and Jobs Act, reduction in net deferred tax liability		23,600
Increase/decrease in valuation allowance	32,800	57,500
Unrecognized tax benefits	28,625	21,613	$ 15,395	$ 13,980
Unrecognized income tax accrued interest and penalties	0
Research and Development
Schedule Of Income Tax [Line Items]
Net operating loss carryforwards	$ 48,800	35,800
Tax credit carryforwards expiration year	2025
Trulia
Schedule Of Income Tax [Line Items]
Income tax (benefit) expense	$ 15,400	66,000
Trade names and trademarks | Trulia
Schedule Of Income Tax [Line Items]
Non-cash impairment of indefinite-lived intangible assets	69,000	174,000
Indefinite-lived intangible asset					$ 351,000
Federal
Schedule Of Income Tax [Line Items]
Net operating loss carryforwards	1,081,700	1,014,000
State
Schedule Of Income Tax [Line Items]
Net operating loss carryforwards	$ 32,500	$ 21,400