Segment Information and Revenue - Revenue Categories (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Revenue:
Total revenue		$ 1,125,821	$ 454,104
Costs and expenses:
Cost of revenue	[1]	761,672	151,348
Sales and marketing		204,648	161,587
Technology and development		134,918	107,770
General and administrative		92,285	95,774
Equity Securities without Readily Determinable Fair Value, Impairment Loss, Annual Amount		76,800	0
Integration costs		0	352
Total costs and expenses		1,270,323	516,831
Loss from operations		(144,502)	(62,727)
Other income		9,593	9,168
Interest expense		(37,592)	(16,466)
Loss before income taxes		(172,501)	(70,025)
Homes
Revenue:
Total revenue		769,873	128,472
Costs and expenses:
Cost of revenue	[1]	732,199	122,419
Sales and marketing		71,589	20,862
Technology and development		32,538	12,281
General and administrative		23,421	14,357
Equity Securities without Readily Determinable Fair Value, Impairment Loss, Annual Amount		0	0
Integration costs		0	0
Total costs and expenses		859,747	169,919
Loss from operations		(89,874)	(41,447)
Other income		0	0
Interest expense		(8,084)	(3,758)
Loss before income taxes		(97,958)	(45,205)
Homes | Zillow Offers
Revenue:
Total revenue		769,112	128,472
Homes | Premier Agent
Revenue:
Total revenue		0	0
Homes | Other
Revenue:
Total revenue		761	0
Homes | Mortgages
Revenue:
Total revenue		0	0
IMT
Revenue:
Total revenue		330,666	298,272
Costs and expenses:
Cost of revenue	[1]	24,318	24,251
Sales and marketing		120,173	126,654
Technology and development		95,028	87,969
General and administrative		58,754	70,850
Equity Securities without Readily Determinable Fair Value, Impairment Loss, Annual Amount		73,900	0
Integration costs		0	0
Total costs and expenses		372,173	309,724
Loss from operations		(41,507)	(11,452)
Other income		0	0
Interest expense		0	0
Loss before income taxes		(41,507)	(11,452)
IMT | Zillow Offers
Revenue:
Total revenue		0	0
IMT | Premier Agent
Revenue:
Total revenue		242,106	217,735
IMT | Other
Revenue:
Total revenue		88,560	80,537
IMT | Mortgages
Revenue:
Total revenue		0	0
Mortgages Segment
Revenue:
Total revenue		25,282	27,360
Costs and expenses:
Cost of revenue	[1]	5,155	4,678
Sales and marketing		12,886	14,071
Technology and development		7,352	7,520
General and administrative		10,110	10,567
Equity Securities without Readily Determinable Fair Value, Impairment Loss, Annual Amount		2,900	0
Integration costs		0	352
Total costs and expenses		38,403	37,188
Loss from operations		(13,121)	(9,828)
Other income		202	313
Interest expense		(226)	(101)
Loss before income taxes		(13,145)	(9,616)
Mortgages Segment | Zillow Offers
Revenue:
Total revenue		0	0
Mortgages Segment | Premier Agent
Revenue:
Total revenue		0	0
Mortgages Segment | Other
Revenue:
Total revenue		0	0
Mortgages Segment | Mortgages
Revenue:
Total revenue		$ 25,282	$ 27,360

[1] Amortization of website development costs and intangible assets included in technology and development of $0 and $14,400 for the three months ended March 31, 2020 and 2019.