Net Loss Per Share - Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) - $ / shares shares in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
September 1, 2026 \| Convertible Debt
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Conversion Spread (in shares)	11,492
Conversion Price per Share (usd per share)	$ 43.51
September 1, 2024 \| Convertible Debt
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Conversion Spread (in shares)	15,468
Conversion Price per Share (usd per share)	$ 43.51
1.50% convertible senior notes due 2023 \| Convertible Debt
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Conversion Spread (in shares)	4,769
Conversion Price per Share (usd per share)	$ 78.37
December 1, 2021 \| Convertible Debt
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Conversion Spread (in shares)	8,785
Conversion Price per Share (usd per share)	$ 52.36
Class A Common Stock and Class C Capital Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total Class A common stock and Class C capital stock equivalents (in shares)	31,693	25,689
Class A Common Stock and Class C Capital Stock \| Weighted average \| Option Awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total Class A common stock and Class C capital stock equivalents (in shares)	23,663	19,408
Class A Common Stock and Class C Capital Stock \| Weighted average \| Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total Class A common stock and Class C capital stock equivalents (in shares)	7,623	5,860
Class A Common Stock \| December 15, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total Class A common stock and Class C capital stock equivalents (in shares)	407	421

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

+ Details

Name:	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

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

- Definition

The price per share of the conversion feature embedded in the debt instrument.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031898-161870

+ Details

Name:	us-gaap_DebtInstrumentConvertibleConversionPrice1
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of convertible debt securities using the if-converted method.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 40
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109260490&loc=d3e1930-109256

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

+ Details

Name:	us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Details

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

- Details

Name:	us-gaap_StatementClassOfStockAxis=z_CommonClassAAndClassCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_WeightedAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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