Contractual interest rate for funds borrowed, under the debt agreement.

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the aggregate of total long-term debt, including current maturities and short-term debt.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtLongtermAndShorttermCombinedAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16(a))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

Name:	us-gaap_SeniorNotes
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19)(a))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16)(a)(1))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

Name:	us-gaap_ShortTermBorrowings
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying value as of the balance sheet date of the outstanding short-term borrowings under a revolving line of credit used by mortgage bankers to finance the origination or purchase of loans.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

Name:	us-gaap_WarehouseAgreementBorrowings
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_ConvertibleDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=z_ConvertibleSeniorNotesdue20261.375Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=z_ConvertibleSeniorNotesDue2025275Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=z_ConvertibleSeniorNotesdue20240.75Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=z_ConvertibleSeniorNotesdue20231.50Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=z_ConvertibleSeniorNotesDue202120Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=z_ConvertibleSeniorNotesDue2020275Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=z_MortgagesSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=z_HomesSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=z_GoldmanSachsBankUSAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=z_CitibankN.A.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=z_CreditSuisseAGCaymanIslandsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=z_ComericaBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt - Schedule of Carrying Value of Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2020	May 19, 2020	May 15, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Total	$ 2,007,010			$ 2,274,990
Convertible Debt
Debt Instrument [Line Items]
Convertible senior notes	$ 1,819,978			1,553,039
Convertible Debt \| 1.375% convertible senior notes due 2026
Debt Instrument [Line Items]
Stated Interest Rate	1.375%
Convertible senior notes	$ 337,171			327,187
Convertible Debt \| 2.75% convertible senior notes due 2025
Debt Instrument [Line Items]
Stated Interest Rate	2.75%	2.75%	2.75%
Convertible senior notes	$ 401,786			0
Convertible Debt \| 0.75% convertible senior notes due 2024
Debt Instrument [Line Items]
Stated Interest Rate	0.75%
Convertible senior notes	$ 507,039			490,538
Convertible Debt \| 1.50% convertible senior notes due 2023
Debt Instrument [Line Items]
Stated Interest Rate	1.50%
Convertible senior notes	$ 318,348			310,175
Convertible Debt \| 2.00% convertible senior notes due 2021
Debt Instrument [Line Items]
Stated Interest Rate	2.00%
Convertible senior notes	$ 245,997			415,502
Convertible Debt \| 2.75% convertible senior notes due 2020
Debt Instrument [Line Items]
Stated Interest Rate	2.75%
Convertible senior notes	$ 9,637			9,637
Mortgages Segment
Debt Instrument [Line Items]
Warehouse line of credit	69,814			30,427
Line of Credit \| Homes Segment
Debt Instrument [Line Items]
Short-term debt	117,218			691,524
Goldman Sachs Bank USA \| Line of Credit \| Homes Segment
Debt Instrument [Line Items]
Short-term debt	19,632			39,244
Citibank, N.A. \| Mortgages Segment
Debt Instrument [Line Items]
Short-term debt	33,918			394
Citibank, N.A. \| Line of Credit \| Homes Segment
Debt Instrument [Line Items]
Short-term debt	33,037			296,369
Credit Suisse AG, Cayman Islands \| Line of Credit \| Homes Segment
Debt Instrument [Line Items]
Short-term debt	64,549			355,911
Comerica Bank \| Line of Credit \| Mortgages Segment
Debt Instrument [Line Items]
Warehouse line of credit	$ 35,896			$ 30,033