Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Income Tax [Line Items]
Income tax benefit	$ 4,258,000	$ 31,102,000	$ 89,586,000
Non-cash impairment of indefinite-lived intangible assets	0
Adjustment to income tax (benefit) under the Tax Act		5,900,000
Remaining tax benefit related to Tax Act			23,600,000
Income tax benefit, Tax Cuts and Jobs Act, reduction in net deferred tax liability	39,300,000	32,800,000
Unrecognized tax benefits	39,432,000	28,625,000	21,613,000	$ 15,395,000
Unrecognized income tax accrued interest and penalties	0
Research And Development
Schedule Of Income Tax [Line Items]
Net operating loss carryforwards	71,000,000.0	48,800,000
Federal
Schedule Of Income Tax [Line Items]
Net operating loss carryforwards	1,137,600,000	1,081,700,000
State
Schedule Of Income Tax [Line Items]
Net operating loss carryforwards	$ 34,300,000	32,500,000
Trulia
Schedule Of Income Tax [Line Items]
Income tax benefit		15,400,000	66,000,000.0
Non-cash impairment of indefinite-lived intangible assets			174,000,000.0
Trulia | Trade names and trademarks
Schedule Of Income Tax [Line Items]
Non-cash impairment of indefinite-lived intangible assets		$ 69,000,000.0	$ 174,000,000.0