Segment Information and Revenue - Revenue Categories (Detail) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2020		Sep. 30, 2019		Sep. 30, 2020	Sep. 30, 2019
Revenue:
Total revenue	$ 656,692		$ 745,208		$ 2,550,865	$ 1,798,890
Costs and expenses:
Cost of revenue	216,224	[1]	399,835	[1]	1,438,967	822,404
Sales and marketing	150,826		181,347		511,072	530,367
Technology and development	127,300		123,974		391,075	352,074
General and administrative	85,895		88,493		263,691	267,106
Impairment costs	0		0		76,800	0
Integration costs	0		5		0	650
Total costs and expenses	580,245		793,654		2,681,605	1,972,601
Income (loss) from operations	76,447		(48,446)		(130,740)	(173,711)
Other income	3,018		8,999		22,726	27,625
Interest expense	(39,470)		(26,502)		(114,652)	(61,865)
Income (loss) before income taxes	39,995		(65,949)		(216,275)	(207,951)
Homes
Revenue:
Total revenue	187,105		384,626		1,411,230	762,022
Costs and expenses:
Cost of revenue	179,804	[1]	370,796	[1]	1,343,791	733,947
Sales and marketing	32,714		49,186		152,180	107,457
Technology and development	28,273		20,651		89,729	51,130
General and administrative	20,334		22,174		65,657	54,339
Impairment costs					0	0
Integration costs	0		0		0	0
Total costs and expenses	261,125		462,807		1,651,357	946,873
Income (loss) from operations	(74,020)		(78,181)		(240,127)	(184,851)
Other income	0		0		0	0
Interest expense	(1,597)		(9,689)		(13,506)	(19,346)
Income (loss) before income taxes	(75,617)		(87,870)		(253,633)	(204,197)
Homes | Zillow Offers
Revenue:
Total revenue	185,904		384,626		1,408,832	762,022
Homes | Premier Agent
Revenue:
Total revenue	0		0		0	0
Homes | Other
Revenue:
Total revenue	1,201		0		2,398	0
Homes | Mortgages
Revenue:
Total revenue	0		0		0	0
IMT
Revenue:
Total revenue	415,389		335,290		1,026,394	957,231
Costs and expenses:
Cost of revenue	28,448	[1]	24,318	[1]	76,153	74,628
Sales and marketing	102,902		118,514		319,101	380,608
Technology and development	90,536		94,656		278,740	276,886
General and administrative	53,547		55,749		166,185	181,270
Impairment costs					73,900	0
Integration costs	0		0		0	0
Total costs and expenses	275,433		293,237		914,079	913,392
Income (loss) from operations	139,956		42,053		112,315	43,839
Other income	0		0		5,300	0
Interest expense	0		0		0	0
Income (loss) before income taxes	139,956		42,053		117,615	43,839
IMT | Zillow Offers
Revenue:
Total revenue	0		0		0	0
IMT | Premier Agent
Revenue:
Total revenue	298,673		240,698		732,741	690,394
IMT | Other
Revenue:
Total revenue	116,716		94,592		293,653	266,837
IMT | Mortgages
Revenue:
Total revenue	0		0		0	0
Mortgages Segment
Revenue:
Total revenue	54,198		25,292		113,241	79,637
Costs and expenses:
Cost of revenue	7,972	[1]	4,721	[1]	19,023	13,829
Sales and marketing	15,210		13,647		39,791	42,302
Technology and development	8,491		8,667		22,606	24,058
General and administrative	12,014		10,570		31,849	31,497
Impairment costs					2,900	0
Integration costs	0		5		0	650
Total costs and expenses	43,687		37,610		116,169	112,336
Income (loss) from operations	10,511		(12,318)		(2,928)	(32,699)
Other income	636		344		1,223	1,059
Interest expense	(553)		(280)		(1,086)	(668)
Income (loss) before income taxes	10,594		(12,254)		(2,791)	(32,308)
Mortgages Segment | Zillow Offers
Revenue:
Total revenue	0		0		0	0
Mortgages Segment | Premier Agent
Revenue:
Total revenue	0		0		0	0
Mortgages Segment | Other
Revenue:
Total revenue	0		0		0	0
Mortgages Segment | Mortgages
Revenue:
Total revenue	$ 54,198		$ 25,292		$ 113,241	$ 79,637

[1] Amortization of website development costs and intangible assets included in technology and development of $19,245 and $15,835 for the three months ended September 30, 2020 and 2019, respectively and $55,286 and $44,891 for the nine months ended September 30, 2020 and 2019, respectively.