Zillow (ZG) 10-K 17 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Jun. 30, 2014	Feb. 04, 2015
Document Information [Line Items]
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Trading Symbol	Z
Entity Registrant Name	ZILLOW INC
Entity Central Index Key	1334814
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Public Float		$4,627,866,009
Class A Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding			34,614,982
Class B Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding			6,217,447

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$125,765	$201,760
Short-term investments	246,829	93,531
Accounts receivable, net of allowance for doubtful accounts of $2,811 and $1,850 at December 31, 2014 and 2013, respectively	18,684	15,234
Prepaid expenses and other current assets	10,059	4,987
Total current assets	401,337	315,512
Long-term investments	83,326	142,435
Property and equipment, net	41,600	27,408
Goodwill	96,352	93,213
Intangible assets, net	26,757	29,149
Other assets	358	346
Total assets	649,730	608,063
Current liabilities:
Accounts payable	9,358	4,724
Accrued expenses and other current liabilities	16,883	10,601
Accrued compensation and benefits	6,735	4,440
Deferred revenue	15,356	12,298
Deferred rent, current portion	864	546
Total current liabilities	49,196	32,609
Deferred rent, net of current portion	11,755	7,658
Commitments and contingencies (Note 12)
Shareholders' equity:
Preferred stock, $0.0001 par value; 30,000,000 shares authorized as of December 31, 2014 and 2013; no shares issued and outstanding as of December 31, 2014 and 2013
Additional paid-in capital	716,506	651,913
Accumulated deficit	-127,731	-84,121
Total shareholders' equity	588,779	567,796
Total liabilities and shareholders' equity	649,730	608,063
Class A Common Stock
Shareholders' equity:
Common stock	3	3
Total shareholders' equity	3	3
Class B Common Stock
Shareholders' equity:
Common stock	1	1
Total shareholders' equity	$1	$1

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Accounts receivable, allowance for doubtful accounts	$2,811	$1,850
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	30,000,000	30,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Class A Common Stock
Common stock, par value	$0.00	$0.00
Common stock, shares authorized	600,000,000	600,000,000
Common stock, shares issued	34,578,393	32,934,074
Common stock, shares outstanding	34,578,393	32,934,074
Class B Common Stock
Common stock, par value	$0.00	$0.00
Common stock, shares authorized	15,000,000	15,000,000
Common stock, shares issued	6,217,447	6,468,892
Common stock, shares outstanding	6,217,447	6,468,892

Consolidated_Statements_of_Ope

Consolidated Statements of Operations (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Income Statement [Abstract]
Revenue	$325,893		$197,545		$116,850
Costs and expenses:
Cost of revenue (exclusive of amortization)	29,461	[1]	18,810	[1]	14,043	[1]
Sales and marketing	167,725		108,891		49,105
Technology and development	86,406		48,498		26,614
General and administrative	65,503		37,919		20,024
Acquisition-related costs	21,493		376		1,267
Total costs and expenses	370,588		214,494		111,053
Income (loss) from operations	-44,695		-16,949		5,797
Other income	1,085		385		142
Income (loss) before income taxes	-43,610		-16,564		5,939
Income tax benefit			4,111
Net income (loss)	($43,610)		($12,453)		$5,939
Net income (loss) per share -basic	($1.09)		($0.35)		$0.20
Net income (loss) per share -diluted	($1.09)		($0.35)		$0.18
Weighted-average shares outstanding -basic	40,009		36,029		30,194
Weighted-average shares outstanding -diluted	40,009		36,029		32,709
[1]	Amortization of website development costs and intangible assets included in technology and development $ 29,487 $ 19,791 $ 11,179

Consolidated_Statements_of_Ope1

Consolidated Statements of Operations (Parenthetical) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement [Abstract]
Amortization of website development costs and intangible assets included in technology and development	$29,487	$19,791	$11,179

Consolidated_Statements_of_Sha

Consolidated Statements of Shareholders' Equity (USD $)	Total	Additional Paid-in Capital	Accumulated Deficit	Class A Common Stock	Class B Common Stock
In Thousands, except Share data
Beginning Balance at Dec. 31, 2011	$101,213	$178,817	($77,607)	$2	$1
Beginning Balance (in shares) at Dec. 31, 2011				18,580,292	9,528,313
Issuance of Class A common stock upon exercise of stock options	7,448	7,448
Issuance of Class A common stock upon exercise of stock options (in shares)				1,624,304,000
Share-based compensation expense	8,990	8,990
Conversion of Class B common stock to Class A common stock (in shares)				2,065,787	-2,065,787
Issuance of Class A common stock in connection with public offering, net of issuance costs of $12,900 for the year ended December 31, 2013 and $8601 for the year ended December 31, 2012	156,727	156,726		1
Issuance of Class A common stock in connection with public offering (in shares)				3,844,818
Issuance of restricted shares of Class A common stock				299,213
Net income (loss) and total comprehensive income (loss)	5,939		5,939
Ending Balance at Dec. 31, 2012	280,317	351,981	-71,668	3	1
Ending Balance (in shares) at Dec. 31, 2012				26,414,414	7,462,526
Issuance of Class A common stock upon exercise of stock options	18,350	18,350
Issuance of Class A common stock upon exercise of stock options (in shares)				2,025,660
Fair value of stock options assumed in connection with an acquisition	430	430
Share-based compensation expense	27,253	27,253
Conversion of Class B common stock to Class A common stock (in shares)				993,634	-993,634
Issuance of Class A common stock in connection with public offering, net of issuance costs of $12,900 for the year ended December 31, 2013 and $8601 for the year ended December 31, 2012	253,899	253,899
Issuance of Class A common stock in connection with public offering (in shares)				3,253,522
Issuance of restricted shares of Class A common stock				252,114
Cancellation of restricted shares of Class A common stock				-5,270
Net income (loss) and total comprehensive income (loss)	-12,453		-12,453
Ending Balance at Dec. 31, 2013	567,796	651,913	-84,121	3	1
Ending Balance (in shares) at Dec. 31, 2013				32,934,074	6,468,892
Issuance of Class A common stock upon exercise of stock options	23,923	23,923
Issuance of Class A common stock upon exercise of stock options (in shares)				1,323,509
Share-based compensation expense	40,670	40,670
Conversion of Class B common stock to Class A common stock (in shares)				251,445	-251,445
Issuance of restricted shares of Class A common stock				69,365
Net income (loss) and total comprehensive income (loss)	-43,610		-43,610
Ending Balance at Dec. 31, 2014	$588,779	$716,506	($127,731)	$3	$1
Ending Balance (in shares) at Dec. 31, 2014				34,578,393	6,217,447

Consolidated_Statements_of_Sha1

Consolidated Statements of Shareholders' Equity (Parenthetical) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Statement of Stockholders' Equity [Abstract]
Stock issuance costs	$12,900	$8,601

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating activities
Net income (loss)	($43,610)	($12,453)	$5,939
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	35,624	23,254	12,773
Share-based compensation expense	34,085	23,436	6,611
Release of valuation allowance on certain deferred tax assets		-4,111
Loss on disposal of property and equipment	505	910	353
Bad debt expense	2,529	1,907	1,227
Deferred rent	4,415	400	5,469
Amortization of bond premium	3,506	624	751
Impairment of certain acquired intangible assets	3,259
Changes in operating assets and liabilities:
Accounts receivable	-5,979	-7,571	-3,458
Prepaid expenses and other assets	-5,084	-1,543	650
Accounts payable	4,634	1,497	991
Accrued expenses	8,577	1,038	1,776
Deferred revenue	3,058	3,910	2,530
Net cash provided by operating activities	45,519	31,298	35,612
Investing activities
Proceeds from investment maturities	174,949	53,000	28,434
Purchases of investments	-272,644	-236,147	-38,397
Purchases of property and equipment	-32,595	-22,047	-15,991
Purchases of intangible assets	-11,647	-3,925	-4,073
Acquisitions, net of cash acquired of $2,879 in 2012	-3,500	-42,708	-67,645
Net cash used in investing activities	-145,437	-251,827	-97,672
Financing activities
Proceeds from exercise of Class A common stock options	23,923	18,350	7,448
Proceeds from public offering, net of offering costs		253,899	156,726
Net cash provided by financing activities	23,923	272,249	164,174
Net increase (decrease) in cash and cash equivalents during period	-75,995	51,720	102,114
Cash and cash equivalents at beginning of period	201,760	150,040	47,926
Cash and cash equivalents at end of period	125,765	201,760	150,040
Noncash transactions:
Capitalized share-based compensation	6,585	3,817	2,379
Write-off of fully depreciated property and equipment	$4,749	$3,697	$2,986

Consolidated_Statements_of_Cas1

Consolidated Statements of Cash Flows (Parenthetical) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2012
Statement of Cash Flows [Abstract]
Convertible Preferred Stock	$2,879

Organization_and_Description_o

Organization and Description of Business	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Organization and Description of Business	Note 1. Organization and Description of Business
	Zillow, Inc. (the “Company,” “Zillow,” “we,” “us” and “our”) was incorporated as a Washington corporation effective December 13, 2004, and we launched the initial version of our website, Zillow.com, in February 2006. Zillow operates the leading real estate and home-related information marketplaces on mobile and the Web, with a complementary portfolio of brands and products to help people find vital information about homes and connect with local professionals. In addition to our living database of homes, accessible on Zillow.com, we also own and operate Zillow Mobile, our suite of home-related mobile applications, Zillow Mortgages, where borrowers connect with lenders to find loans and get competitive mortgage rates, Zillow Digs, our home improvement marketplace where consumers can find visual inspiration and local cost estimates, Zillow Rentals, a marketplace and suite of tools for rental professionals, Postlets, Diverse Solutions, Mortech, HotPads, StreetEasy and Retsly. Zillow provides products and services to help consumers through every stage of homeownership—buying, selling, renting, borrowing and remodeling.
	Proposed Acquisition of Trulia, Inc.
	On July 28, 2014, Zillow, Zebra Holdco, Inc., a Washington corporation (“HoldCo”), and Trulia, Inc., a Delaware corporation (“Trulia”), entered into an Agreement and Plan of Merger (the “Merger Agreement”), pursuant to which Zillow agreed to acquire Trulia. Trulia’s mobile and web products provide buyers, sellers, renters and real estate professionals with tools and information for the home search process and provide agents with an end-to-end technology platform that enables them to find and serve clients.
	The Merger Agreement provides that, upon the terms and subject to the conditions set forth therein, (i) a newly-organized Washington corporation, and wholly owned subsidiary of HoldCo (“Zillow Merger Sub”), will merge with and into Zillow (the “Zillow Merger”), with Zillow as the surviving entity, and (ii) a newly-organized Delaware corporation, and wholly-owned subsidiary of HoldCo (“Trulia Merger Sub”), will merge with and into Trulia (the “Trulia Merger” and, together with the Zillow Merger, the “Mergers”), with Trulia as the surviving entity. As a result of the Mergers, both Zillow and Trulia will become wholly-owned subsidiaries of HoldCo. Pursuant to the terms of the Merger Agreement, at the effective time of the Zillow Merger (the “Zillow Merger Effective Time”), (x) each share of Zillow’s Class A common stock will be converted into the right to receive one share of Class A common stock of HoldCo (“HoldCo Class A Common Stock”), and (y) each share of Zillow’s Class B common stock will be converted into the right to receive one share of Class B common stock of HoldCo. The Merger Agreement provides that, at the Zillow Merger Effective Time, all Zillow equity awards outstanding as of immediately prior to the Zillow Merger Effective Time will be assumed by HoldCo. In addition, pursuant to the terms of the Merger Agreement, at the effective time of the Trulia Merger (the “Trulia Merger Effective Time”), by virtue of the Trulia Merger and without any action on the part of any stockholder, each share of Trulia common stock will be converted into the right to receive 0.444 of a share of HoldCo Class A Common Stock. The Merger Agreement provides that, at the Trulia Merger Effective Time, all Trulia equity awards outstanding as of immediately prior to the Trulia Merger Effective Time will be assumed by HoldCo. The Trulia Merger Effective Time is expected to occur promptly after the Zillow Merger Effective Time. Upon consummation of the merger, Holdco Class A Common Stock is expected to be listed for trading on the NASDAQ Global Select Market.
	The consummation of each of the Zillow Merger and the Trulia Merger is subject to customary conditions, including: (a) absence of any applicable restraining order or injunction prohibiting the Mergers; (b) absence of a material adverse effect with respect to each of Zillow and Trulia; (c) accuracy of the representations and warranties of each party, subject to specified materiality thresholds; (d) performance in all material respects by each party of its obligations under the Merger Agreement; (e) authorization for listing the HoldCo Class A Common Stock on the NASDAQ Global Select Market; and (f) with respect to Zillow, the absence of certain legal proceedings that seek to restrain the Mergers or restrict the businesses of Zillow or Trulia.
	The Merger Agreement contains termination rights for Trulia and Zillow applicable upon: (1) a final non-appealable order or other action prohibiting the Mergers; (2) the eighteen-month anniversary of the date of the Merger Agreement; (3) a breach by the other party that cannot be cured within 30 days’ notice of such breach, if such breach would result in the failure of the conditions to closing set forth in the Merger Agreement; (4) certain “triggering events,” including a change in recommendation relating to the Mergers by the other party’s Board; and (5) in certain circumstances, Trulia’s entry into a contract with respect to a superior proposal.
	If the Merger Agreement is terminated in certain circumstances, Zillow or Trulia, as applicable, would be required to pay the other a termination fee of $69.8 million. In addition, the Merger Agreement provides that, in certain other circumstances, Zillow would be required to pay Trulia a termination fee of $150 million.
	On September 12, 2014, HoldCo filed a Registration Statement on Form S-4 with the SEC to register the shares of HoldCo’s common stock that will be issued to shareholders of Zillow and stockholders of Trulia as consideration in the proposed acquisition in exchange for the Zillow and Trulia common stock. The Registration Statement on Form S-4 was declared effective by the SEC on November 17, 2014. On December 18, 2014, Zillow’s shareholders and Trulia’s stockholders approved the mergers. On February 13, 2015, Zillow announced that it received notification from the Federal Trade Commission (“FTC”) that the FTC closed its investigation and would take no action against the proposed transaction. As a result, closing conditions related to the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, have been satisfied. The proposed transaction remains subject to the satisfaction of a number of customary closing conditions, and Zillow anticipates that it will be completed as early as February 17, 2015. During the year ended December 31, 2014, Zillow incurred a total of $21.3 million in acquisition-related costs related to the transaction, which includes $5.0 million of investment banking fees.
	Certain Significant Risks and Uncertainties
	We operate in a dynamic industry and, accordingly, can be affected by a variety of factors. For example, we believe that changes in any of the following areas could have a significant negative effect on us in terms of our future financial position, results of operations or cash flows: our ability to successfully integrate and realize the benefits of our past or future strategic acquisitions or investments, including our proposed acquisition of Trulia; rates of revenue growth; engagement and usage of our products; scaling and adaptation of existing technology and network infrastructure; competition in our market; management of our growth; qualified employees and key personnel; protection of our brand and intellectual property; changes in government regulation affecting our business; intellectual property infringement and other claims; protection of customers’ information and privacy concerns; and security measures related to our mobile applications and websites, among other things.

Summary_of_Significant_Account

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Note 2. Summary of Significant Accounting Policies
	Basis of Presentation
	The accompanying consolidated financial statements include Zillow, Inc. and our wholly-owned subsidiary, Zillow (Canada), Inc. All significant intercompany balances and transactions have been eliminated in consolidation. These consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“GAAP”).
	Use of Estimates
	The preparation of financial statements in conformity with GAAP requires management to make certain estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and the related disclosures at the date of the financial statements, as well as the reported amounts of revenue and expenses during the periods presented. On an ongoing basis, we evaluate our estimates, including those related to revenue recognition, the allowance for doubtful accounts, website development costs, goodwill, recoverability of intangible assets with definite lives and other long-lived assets, and for share-based compensation, among others. To the extent there are material differences between these estimates, judgments, or assumptions and actual results, our financial statements will be affected. In many cases, the accounting treatment of a particular transaction is specifically dictated by GAAP and does not require management’s judgment in its application.
	Reclassifications
	Certain immaterial reclassifications have been made in the consolidated balance sheets and statements of operations to conform data for prior periods to the current format.
	Concentrations of Credit Risk
	Financial instruments, which potentially subject us to concentrations of credit risk, consist primarily of cash and cash equivalents, investments and accounts receivable. We place cash and cash equivalents and investments with major financial institutions, which management assesses to be of high credit quality, in order to limit exposure of our investments.
	Credit risk with respect to accounts receivable is dispersed due to the large number of customers. Further, our credit risk on accounts receivable is mitigated by the relatively short payment terms that we offer. Collateral is not required for accounts receivable. We maintain an allowance for doubtful accounts such that receivables are stated at net realizable value.
	Cash and Cash Equivalents
	Cash includes currency on hand as well as demand deposits with banks or financial institutions. Cash equivalents include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Our cash equivalents include only investments with original maturities of three months or less. We regularly maintain cash in excess of federally insured limits at financial institutions.
	Investments
	Our investments consist of fixed income securities, which include U.S. government agency securities, corporate notes and bonds, municipal securities, commercial paper and certificates of deposit. Securities with maturities greater than three months but less than one year are classified as short-term investments. Securities with maturities greater than one year are classified as long-term investments. Our investments are classified as held-to-maturity and are recorded at amortized cost, as we do not intend to sell the investments, and it is not more likely than not that we will be required to sell these investments prior to maturity. The amortized cost of our investments approximates their fair value.
	We have restricted investment balances primarily used to guarantee various letters of credit (see Note 12). The restricted investment balances are carried at cost, which approximates fair value.
	Accounts Receivable and Allowance for Doubtful Accounts
	Accounts receivable are generally due within 30 days and are recorded net of the allowance for doubtful accounts. We consider accounts outstanding longer than the contractual terms past due. We review accounts receivable on a regular basis and estimate an amount of losses for uncollectible accounts based on our historical collections experience, age of the receivable, knowledge of the customer and the condition of the general economy and industry as a whole. We record changes in our estimate to the allowance for doubtful accounts through bad debt expense and relieve the allowance when accounts are ultimately determined to be uncollectible. Bad debt expense is included in general and administrative expenses.
	Property and Equipment
	Property and equipment is recorded at cost and depreciated using the straight-line method over the estimated useful lives of the related assets. The useful lives are as follows:
	Computer equipment	3 years
	Purchased software	3 years
	Office equipment, furniture and fixtures	5 to 7 years
	Leasehold improvements	Shorter of expected useful life or lease term
	Maintenance and repair costs are charged to expense as incurred. Major improvements, which extend the useful life of the related asset, are capitalized. Upon disposal of a fixed asset, we record a gain or loss based on the differences between the proceeds received and the net book value of the disposed asset.
	Website and Software Development Costs
	The costs incurred in the preliminary stages of development are expensed as incurred. Once an application has reached the development stage, internal and external costs, if direct and incremental and deemed by management to be significant, are capitalized in property and equipment and amortized on a straight-line basis over their estimated useful lives. Maintenance and enhancement costs, including those costs in the post-implementation stages, are typically expensed as incurred, unless such costs relate to substantial upgrades and enhancements to the website or software that result in added functionality, in which case the costs are capitalized and amortized on a straight-line basis over the estimated useful lives. Amortization expense related to capitalized website and software development costs is included in technology and development expense.
	Capitalized development activities placed in service are amortized over the expected useful lives of those releases, currently estimated at one year. The estimated useful lives of website and software development activities are reviewed frequently and adjusted as appropriate to reflect upcoming development activities that may include significant upgrades and/or enhancements to the existing functionality.
	Goodwill
	Goodwill represents the excess of the cost of an acquired business over the fair value of the assets acquired at the date of acquisition. We assess the impairment of goodwill on an annual basis, in our fourth quarter, or whenever events or changes in circumstances indicate that goodwill may be impaired.
	We assess goodwill for possible impairment by first performing a qualitative assessment to determine whether it is more likely than not that the fair value of our reporting unit is less than its carrying amount. If we determine that it is not more likely than not that the fair value of our reporting unit is less than its carrying amount, then the first and second steps of the goodwill impairment test are unnecessary. If we determine that it is more likely than not that the fair value of our reporting unit is less than its carrying amount, we perform the two-step goodwill impairment test. The first step of the goodwill impairment test identifies if there is potential goodwill impairment. If step one indicates that an impairment may exist, a second step is performed to measure the amount of the goodwill impairment, if any. Goodwill impairment exists when the estimated fair value of goodwill is less than its carrying value. If impairment exists, the carrying value of the goodwill is reduced to fair value through an impairment charge recorded in our statements of operations.
	Intangible Assets
	We purchase and license data content from multiple data providers. This data content consists of U.S. county data about home details (e.g., the number of bedrooms, bathrooms, square footage) and other information relating to the purchase price of homes, both current and historical, as well as imagery, mapping and parcel data that is displayed on our mobile applications and websites. Our home details data not only provides information about a home and its related transactions which is displayed on our mobile applications and websites, but is also used in our proprietary valuation algorithms to produce Zestimates, Rent Zestimates and Zillow Home Value Indexes. License agreement terms vary by vendor. In some instances, we retain perpetual rights to this information after the contract ends; in other instances, the information and data are licensed only during the fixed term of the agreement. Additionally, certain data license agreements provide for uneven payment amounts throughout the life of the contract term.
	We capitalize payments made to third parties for data licenses that we expect to provide future economic benefit through the recovery of the costs of these arrangements via the generation of our revenue and margins. For data license contracts that include uneven payment amounts, we capitalize the payments as they are made as an intangible asset and amortize the total contract value over the estimated useful life. For contracts in which we have perpetual rights to the data, the total contract value is amortized on a straight-line basis over the life of the contract plus two years, which is equivalent to the estimated useful life of the asset. For contracts in which we do not have access to the data beyond the contractual term, the total contract value is amortized on a straight line basis over the term of the contract. We evaluate data content contracts for potential capitalization at the inception of the arrangement as well as each time periodic payments to third parties are made.
	The amortization period for the capitalized purchased content is based on our best estimate of the useful life of the asset, which ranges from two to nine years. The determination of the useful life includes consideration of a variety of factors including, but not limited to, our assessment of the expected use of the asset and contractual provisions that may limit the useful life, as well as an assessment of when the data is expected to become obsolete based on our estimates of the diminishing value of the data over time. We evaluate the useful life of the capitalized purchased data content each reporting period to determine whether events and circumstances warrant a revision to the remaining useful life. If we determine the estimate of the asset’s useful life requires modification, the carrying amount of the asset is amortized prospectively over the revised useful life. The capitalized purchased data content is amortized on a straight-line basis as the pattern of delivery of the economic benefits of the data cannot reliably be determined because we do not have the ability to reliably predict future traffic to our websites and mobile applications.
	Under certain other data agreements, the underlying data is obtained on a subscription basis with consistent monthly recurring payment terms over the contractual period. Upon the expiration of such arrangements, we no longer have the right to access the related data, and therefore, the costs incurred under such contracts are not capitalized and are expensed as payments are made. We would immediately lose rights to data under these arrangements if we were to cancel the subscription and/or cease making payments under the subscription arrangements.
	We also have intangible assets for developed technology, customer relationships and trademarks which we recorded in connection with acquisitions. These intangible assets are amortized over the estimated useful life of the asset.
	Recoverability of Intangible Assets with Definite Lives and Other Long-Lived Assets
	We evaluate intangible assets and other long-lived assets for impairment whenever events or circumstances indicate that they may not be recoverable. Recoverability is measured by comparing the carrying amount of an asset group to future undiscounted net cash flows expected to be generated. We group assets for purposes of such review at the lowest level for which identifiable cash flows of the asset group are largely independent of the cash flows of the other groups of assets and liabilities. If this comparison indicates impairment, the amount of impairment to be recognized is calculated as the difference between the carrying value and the fair value of the asset group.
	Deferred Revenue
	Deferred revenue consists of prepaid advertising fees received or billed in advance of the delivery or completion of the services, and for amounts received in instances when revenue recognition criteria have not been met. Deferred revenue is recognized when the services are provided and all revenue recognition criteria have been met.
	Deferred Rent
	For our operating leases, we recognize rent expense on a straight-line basis over the terms of the leases and, accordingly, we record the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. Landlord-funded leasehold improvements are also recorded as deferred rent liabilities and are amortized as a reduction of rent expense over the non-cancelable term of the related operating lease.
	Revenue Recognition
	In general, we recognize revenue when (i) persuasive evidence of an arrangement exists, (ii) delivery has occurred or services have been rendered to the customer, (iii) the fee is fixed or determinable, and (iv) collectability is reasonably assured. We consider a signed agreement, a binding insertion order or other similar documentation reflecting the terms and conditions under which products or services will be provided to be persuasive evidence of an arrangement. Collectability is assessed based on a number of factors, including payment history and the creditworthiness of a customer. If it is determined that collection is not reasonably assured, revenue is not recognized until collection becomes reasonably assured, which is generally upon receipt of cash.
	We generate revenue from the sale of advertising services and our suite of tools to businesses and professionals primarily associated with the real estate and mortgage industries. These professionals include local real estate professionals, mortgage professionals and brand advertisers. Our two revenue categories are marketplace revenue and display revenue. Incremental direct costs incurred related to the acquisition or origination of a customer contract in a transaction that results in the deferral of revenue are expensed as incurred.
	Marketplace Revenue. Marketplace revenue consists of real estate revenue and mortgages revenue. Real estate revenue primarily includes revenue from impressions delivered under our Premier Agent program, as well as revenue generated by Zillow Rentals. Mortgages revenue primarily includes advertising sold to mortgage lenders on a cost-per-click, or CPC, basis, related to Zillow Mortgages, as well as revenue generated by Mortech, which provides subscription-based mortgage software solutions, including a product and pricing engine and lead management platform, for which we recognize revenue on a straight-line basis during the contractual period over which the services are delivered.
	Zillow’s Premier Agent program offers a suite of marketing and business technology solutions to help real estate agents grow their businesses and personal brands. The Premier Agent program allows agents to select products and services that they can tailor to meet their business and advertising needs. The program has three tiers of participation including Premier Platinum, our flagship product, as well as Premier Gold and Premier Silver, to meet different marketing and business needs of a broad range of agents. All tiers of Premier Agents receive access to a dashboard portal on our website that provides individualized program performance analytics, as well as our personalized website service, and our free customer relationship management, or CRM, tool that captures detailed information about each contact made with a Premier Agent through our mobile and web platforms. Our Premier Gold product also includes featured listings whereby the agent’s listings will appear at the top of search results on our mobile and web platforms. Our Premier Platinum product includes the dashboard portal on our website, our personalized website service, our CRM tool, featured listings, and inclusion on our buyer’s agent list, whereby the agent appears as the agent to contact for listings in the purchased zip code.
	We charge for our Platinum Premier Agent product based on the number of impressions delivered on our buyer’s agent list in zip codes purchased and a contracted maximum cost per impression. Our Platinum Premier Agent product includes multiple deliverables which are accounted for as a single unit of accounting, as the delivery or performance of the undelivered elements is based on traffic to our mobile applications and websites. We recognize revenue related to our impression-based Platinum Premier Agent product based on the lesser of (i) the actual number of impressions delivered on our buyer’s agent list during the period multiplied by the contracted maximum cost per impression, or (ii) the contractual maximum spend on a straight-line basis during the contractual period over which the services are delivered, typically over a period of six months or twelve months and then month-to-month thereafter.
	We charge a fixed subscription fee for our Premier Gold and Premier Silver subscription products. Subscription advertising revenue for our Premier Gold and Premier Silver subscription products is recognized on a straight-line basis during the contractual period over which the services are delivered, typically over a period of six months and then month-to-month thereafter.
	In Zillow Mortgages, participating qualified mortgage lenders make a prepayment to gain access to consumers interested in connecting with mortgage professionals. Consumers who request rates for mortgage loans in Zillow Mortgages are presented with personalized lender quotes from participating lenders. We only charge mortgage lenders a fee when users click for more information regarding a mortgage loan quote. Mortgage lenders who exhaust their initial prepayment can then prepay additional funds to continue to participate in the marketplace. We recognize revenue when a user clicks on a mortgage advertisement or to obtain additional information about a mortgage loan quote.
	Display Revenue. Display revenue primarily consists of graphical mobile and web advertising sold on a cost per thousand impressions, or CPM basis, to advertisers primarily in the real estate industry, including real estate brokerages, home builders, mortgage lenders and home services providers. Our advertising customers also include telecommunications, automotive, insurance and consumer products companies. We recognize display revenue as impressions are delivered to users interacting with our mobile applications or websites.
	There were no customers that generated 10% or more of our total revenue in the years ended December 31, 2014, 2013 or 2012.
	Cost of Revenue
	Our cost of revenue consists of expenses related to operating our mobile applications and websites, including associated headcount expenses, such as salaries and benefits and share-based compensation expense and bonuses. Cost of revenue also includes credit card fees, ad serving costs paid to third parties, revenue-sharing costs related to our commercial business relationships, and data center operations costs.
	Research and Development
	Research and development costs are expensed as incurred. For the years ended December 31, 2014, 2013 and 2012, expenses attributable to research and development for our business totaled $72.9 million, $41.7 million and $22.0 million, respectively. Research and development costs are recorded in technology and development expenses.
	Other Income
	Other income consists primarily of interest income earned on our cash, cash equivalents and investments.
	Share-Based Compensation
	We measure compensation expense for all share-based awards at fair value on the date of grant and recognize compensation expense over the service period on a straight-line basis for awards expected to vest.
	We use the Black-Scholes-Merton option-pricing model to determine the fair value for option awards. In valuing our option awards, we make assumptions about risk-free interest rates, dividend yields, volatility, and weighted-average expected lives, including estimated forfeiture rates. Risk-free interest rates are derived from U.S. Treasury securities as of the option award grant date. Expected dividend yield is based on our historical dividend payments, which have been zero to date. The expected volatility for our Class A common stock is estimated using a combination of our historical volatility and the published historical volatilities of industry peers in the online publishing market representing the verticals in which we operate. We estimate the weighted-average expected life of the option awards as the average of the option vesting schedule and the term of the award, since we do not have sufficient historical exercise data to provide a reasonable basis upon which to estimate expected term due to the limited period of time share-based awards have been exercisable. The term of the award is estimated using the simplified method, as awards are plain vanilla option awards. Forfeiture rates are estimated using historical actual forfeiture trends as well as our judgment of future forfeitures. These rates are evaluated at least quarterly and any change in compensation expense is recognized in the period of the change. The estimation of option awards that will ultimately vest requires judgment, and to the extent actual results or updated estimates differ from our current estimates, such amounts will be recorded as a cumulative adjustment in the period the estimates are revised. We consider many factors when estimating expected forfeitures, including employee class and historical experience. Actual results, and future changes in estimates, may differ substantially from management’s current estimates.
	For issuances of restricted stock awards, restricted stock units and restricted units, we determine the fair value of the award based on the market value of our Class A common stock at the date of grant.
	Advertising Costs
	Advertising costs are expensed as incurred. For the years ended December 31, 2014, 2013 and 2012, expenses attributable to advertising totaled $73.1 million, $38.7 million and $11.1 million, respectively. Advertising costs are recorded in sales and marketing expenses.
Income Taxes
We use the asset and liability approach for accounting and reporting income taxes, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the financial statement and tax bases of assets and liabilities at the applicable enacted tax rates. A valuation allowance against deferred tax assets would be established if, based on the weight of available evidence, it is more likely than not (a likelihood of more than 50%) that some or all of the deferred tax assets are not expected to be realized.
We establish reserves for tax-related uncertainties based on estimates of whether, and the extent to which, additional taxes will be due. We adjust these reserves in light of changing facts and circumstances, such as the closing of a tax audit, new tax legislation or the change of an estimate. To the extent that the final tax outcome of these matters is different than the amounts recorded, such differences will affect the provision for income taxes in the period in which such determination is made.
Recently Issued Accounting Standards
In August 2014, the Financial Accounting Standards Board (“FASB”) issued guidance on the disclosure of uncertainties about an entity’s ability to continue as a going concern. This standard provides guidance about management’s responsibility to evaluate whether there is substantial doubt about an entity’s ability to continue as a going concern and to provide related footnote disclosures. The guidance is effective for annual reporting periods ending after December 15, 2016, and early adoption is permitted. We expect to adopt this guidance on January 1, 2017. We do not expect the adoption of this guidance to have any impact on our financial position, results of operations or cash flows.
In May 2014, the FASB issued guidance on revenue recognition. This guidance provides that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This guidance also requires more detailed disclosures to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. This guidance is effective for interim and annual reporting periods beginning after December 15, 2016, early adoption is not permitted, and must be applied retrospectively or modified retrospectively. We expect to adopt this guidance on January 1, 2017. We have not yet determined the impact the adoption of this guidance will have on our financial position, results of operations or cash flows, if any.

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value Measurements	Note 3. Fair Value Measurements
	Accounting standards define fair value as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market in an orderly transaction between market participants on the measurement date. The standards also establish a fair value hierarchy, which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. There are three levels of inputs that may be used to measure fair value:
		•		Level 1—Quoted prices in active markets for identical assets or liabilities.
		•		Level 2—Assets and liabilities valued based on observable market data for similar instruments, such as quoted prices for similar assets or liabilities.
		•		Level 3—Unobservable inputs that are supported by little or no market activity; instruments valued based on the best available data, some of which is internally developed, and considers risk premiums that a market participant would require.
	We applied the following methods and assumptions in estimating our fair value measurements:
	Cash equivalents—Cash equivalents are comprised of highly liquid investments with original maturities of less than three months. The fair value measurement of these assets is based on quoted market prices in active markets and these assets are recorded at fair value.
	Short-term and long-term investments—Our investments consist of fixed income securities, which include U.S. government agency securities, corporate notes and bonds, municipal securities, commercial paper and certificates of deposit. The fair value measurement of these assets is based on observable market-based inputs or inputs that are derived principally from or corroborated by observable market data by correlation or other means.
	Of the short-term investments and long-term investments on hand as of December 31, 2014, 74.8% mature in 2015 and the remaining 25.2% mature in 2016.
	The following tables present the fair value of cash equivalents and investments as of the dates presented (in thousands):
			December 31, 2014
			Total		Level 1		Level 2
	Cash equivalents:
	Money market funds		$	98,645	$	98,645	$	—
	Foreign government securities			9,035		—		9,035
	Certificates of deposit			2,975		—		2,975
	Short-term investments:
	U.S government agency securities			118,342		118,342		—
	Corporate notes and bonds			78,746		—		78,746
	Municipal securities			26,256		—		26,256
	Foreign government securities			8,570		—		8,570
	Commercial paper			7,987		—		7,987
	Certificates of deposit			6,928		—		6,928
	Long-term investments:
	U.S government agency securities			63,515		63,515		—
	Municipal securities			12,917		—		12,917
	Corporate notes and bonds			6,694		—		6,694
	Certificates of deposit			200		—		200
	Total		$	440,810	$	280,502	$	160,308
			31-Dec-13
			Total		Level 1		Level 2
	Cash equivalents:
	Money market funds		$	184,941	$	184,941	$	—
	U.S government agency securities			3,306		3,306		—
	Short-term investments:
	U.S government agency securities			78,448		78,448		—
	Commercial paper			3,998		—		3,998
	Corporate notes and bonds			11,085		—		11,085
	Long-term investments:
	U.S government agency securities			112,623		112,623		—
	Corporate notes and bonds			29,812		—		29,812
	Total		$	424,213	$	379,318	$	44,895
	We did not have any Level 3 assets as of December 31, 2014 or 2013. There were no liabilities measured at fair value as of December 31, 2014 or 2013.

Accounts_Receivable_net

Accounts Receivable, net	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Accounts Receivable, net	Note 4. Accounts Receivable, net
	The following table presents the detail of accounts receivable as of the dates presented (in thousands):
		December 31,
		2014			2013
	Accounts receivable	$	17,373		$	13,793
	Unbilled accounts receivable		4,122			3,291
	Less: allowance for doubtful accounts		(2,811	)		(1,850	)
	Accounts receivable, net	$	18,684		$	15,234
	The following table presents the changes in the allowance for doubtful accounts for the periods presented (in thousands):
		Year Ended December 31,
		2014			2013			2012
	Allowance for doubtful accounts:
	Balance, beginning of period	$	1,850		$	965		$	683
	Additions charged to expense		2,529			1,907			1,227
	Less: write-offs, net of recoveries and other adjustments		(1,568	)		(1,022	)		(945	)
	Balance, end of period	$	2,811		$	1,850		$	965

Property_and_Equipment_net

Property and Equipment, net	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Property and Equipment, net	Note 5. Property and Equipment, net
	The following table presents the detail of property and equipment as of the dates presented (in thousands):
		December 31,
		2014			2013
	Website development costs	$	65,224		$	50,408
	Computer equipment		13,243			8,238
	Leasehold improvements		10,617			7,320
	Software		3,431			1,807
	Construction-in-progress		9,307			3,289
	Office equipment, furniture and fixtures		6,482			3,661
	Property and equipment		108,304			74,723
	Less: accumulated amortization and depreciation		(66,704	)		(47,315	)
	Property and equipment, net	$	41,600		$	27,408
	We recorded amortization and depreciation expense related to property and equipment, other than website development costs, of $6.1 million, $3.5 million and $1.6 million, respectively, during the years ended December 31, 2014, 2013 and 2012.
	We capitalized $22.2 million, $17.3 million and $11.5 million, respectively, in website development costs during the years ended December 31, 2014, 2013 and 2012. Amortization expense for website development costs included in technology and development expenses was $18.3 million, $12.2 million and $6.9 million, respectively, for the years ended December 31, 2014, 2013 and 2012.
	Construction-in-progress primarily consists of website development costs that are capitalizable, but for which the associated applications had not yet been placed in service.

Goodwill

Goodwill	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	Note 6. Goodwill
	The following table presents the change in goodwill from December 31, 2013 through December 31, 2014 (in thousands):
	Balance as of December 31, 2013	$	93,213
	Goodwill recorded in connection with an acquisition		3,139
	Balance as of December 31, 2014	$	96,352
	In June 2014, Zillow entered into an asset purchase agreement, pursuant to which Zillow acquired substantially all of the operating assets, including intellectual property rights and intangible assets, of the acquiree. The acquisition has been accounted for as a business combination, and assets acquired and liabilities assumed were recorded at their estimated fair values as of the acquisition date, and were not significant. The results of operations related to the acquisition have been included in our consolidated financial statements since the date of acquisition, and are not significant. Pro forma financial information for the acquisition accounted for as a business combination has not been presented, as the effects were not material to our consolidated financial statements. The goodwill recorded in connection with the acquisition is deductible for tax purposes.

Intangible_Assets

Intangible Assets	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	Note 7. Intangible Assets
	The following tables present the detail of intangible assets subject to amortization as of the dates presented (in thousands):
		December 31, 2014
		Cost		Accumulated			Net
				Amortization
	Purchased content	$	24,615	$	(13,904	)	$	10,711
	Developed technology		13,595		(5,322	)		8,274
	Customer relationships		9,225		(3,386	)		5,838
	Trademarks		3,261		(1,327	)		1,934
	Total	$	50,696	$	(23,939	)	$	26,757
		December 31, 2013
		Cost		Accumulated			Net
				Amortization
	Purchased content	$	12,968	$	(8,846	)	$	4,122
	Developed technology		18,835		(4,417	)		14,418
	Customer relationships		9,775		(1,799	)		7,976
	Trademarks		3,261		(628	)		2,633
	Total	$	44,839	$	(15,690	)	$	29,149
	In October 2014, we entered into an agreement containing a non-cancelable purchase commitment with escalating payments for content related to our mobile applications and websites that expires in October 2021. The total amount due for this content over the seven year contractual term is approximately $50 million. As the data license obtained under this agreement includes uneven payment amounts, we capitalize the payments as they are made as an intangible asset and amortize the total contract value over the estimated useful life. We have perpetual rights to the data under the agreement. The total contract value is amortized on a straight-line basis over the life of the contract plus two years, which is equivalent to the estimated useful life of the asset.
	Amortization expense recorded for intangible assets for the years ended December 31, 2014, 2013 and 2012 was $11.1 million, $7.6 million and $4.3 million, respectively, and these amounts are included in technology and development expenses. The remaining weighted-average amortization period for all intangible assets as of December 31, 2014 and 2013 was approximately 6.4 years and 4.5 years, respectively.
	For the year ended December 31, 2014, technology and development expense includes $3.3 million related to the impairment of certain acquired intangible assets primarily obtained in connection with our 2012 acquisition of RentJuice Corporation (“RentJuice”). In December 2014, Zillow’s management recommended and Zillow’s Board of Directors approved the shutdown of RentJuice.
	Estimated future amortization expense for intangible assets, including amortization related to future commitments (see Note 12), as of December 31, 2014 is as follows (in thousands):
	2015	$	11,092
	2016		13,514
	2017		10,647
	2018		8,671
	2019		6,900
	All future years		24,128
	Total future amortization expense	$	74,952

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	Note 8. Income Taxes
	We are subject to federal and state income taxes in the United States and Canada. For the years ended December 31, 2014, 2013 and 2012, we did not have a material amount of reportable taxable income and, therefore, no related tax liability or expense has been recorded in the consolidated financial statements. We recorded an income tax benefit of $4.1 million for the year ended December 31, 2013 due to a deferred tax liability generated in connection with Zillow’s August 26, 2013 acquisition of StreetEasy, Inc. that can be used to realize certain deferred tax assets for which we had previously provided a full valuation allowance.
	The following table summarizes the components of our income tax benefit for the periods presented (in thousands):
		Year Ended December 31,
		2014			2013			2012
	Federal	$	—		$	3,783		$	—
	State		—			328			—
	Deferred income tax benefit	$	—		$	4,111		$	—
	The following table presents a reconciliation of the federal statutory rate and our effective tax rate for the periods presented:
		Year Ended December 31,
		2014			2013			2012
	Tax expense at federal statutory rate		(34.0	%)		(34.0	%)		34	%
	State income taxes, net of federal tax benefit		(1.5	%)		(5.8	%)		0	%
	Nondeductible expenses		15.3	%		3.1	%		9.2	%
	Share-based compensation		0.7	%		0.2	%		3.5	%
	Research and development credits		(3.2	%)		(23.3	%)		0	%
	Valuation allowance		22.7	%		35	%		(46.7	%)
	Effective tax rate		0	%		(24.8	%)		0	%
	Deferred federal, state and foreign income taxes reflect the net tax impact of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and such amounts for tax purposes. The following table presents the significant components of our deferred tax assets and liabilities as of the dates presented (in thousands):
		December 31,
		2014			2013
	Deferred tax assets:
	Federal and state net operating loss carryforwards	$	25,665		$	24,152
	Share-based compensation		12,680			4,467
	Goodwill		1,355			1,776
	Start-up and organizational costs		430			491
	Research and development credits		6,493			5,123
	Accruals and reserves		2,339			901
	Deferred rent		4,248			2,666
	Other		167			749
	Total deferred tax assets		53,377			40,325
	Deferred tax liabilities:
	Website and software development costs		(7,263	)		(4,927	)
	Intangibles		(6,052	)		(6,519	)
	Depreciation and amortization		(2,838	)		(1,579	)
	Net deferred tax assets before valuation allowance		37,224			27,300
	Less: valuation allowance		(37,224	)		(27,300	)
	Net deferred tax assets	$	—		$	—
	Realization of deferred tax assets is dependent upon the generation of future taxable income, if any, the timing and amount of which are uncertain. We have provided a full valuation allowance against the net deferred tax assets as of December 31, 2014 and 2013 because, based on the weight of available evidence, it is more likely than not (a likelihood of more than 50%) that some or all of the deferred tax assets will not be realized. The valuation allowance increased by $9.9 million during the year ended December 31, 2014 and increased by $5.9 million during the year ended December 31, 2013.
	We have accumulated federal tax losses of approximately $358.6 million and $236.5 million as of December 31, 2014 and 2013, respectively, which are available to reduce future taxable income. We have accumulated state tax losses of approximately $7.2 million and $6.1 million (tax effected) as of December 31, 2014 and 2013. As of December 31, 2014, approximately $286.1 million of our net operating loss carryforwards relate to tax deductible share-based compensation in excess of amounts recognized for financial reporting purposes. To the extent that net operating loss carryforwards, if realized, relate to share-based compensation, the resulting tax benefits will be recorded to shareholders’ equity rather than to the statement of operations. Additionally, we have research and development credit carryforwards of $6.5 million and $5.1 million, respectively, as of December 31, 2014 and 2013, which are available to reduce future tax liabilities. The tax loss and research and development credit carryforwards begin to expire in 2025. Under Sections 382 and 383 of the Internal Revenue Code, if a corporation undergoes an ownership change, the corporation’s ability to use its pre-change net operating loss carryforwards and other pre-change tax attributes, such as research tax credits, to offset its post-change income or income tax liability may be limited. In connection with our August 2013 public offering of our Class A Common stock, we experienced an ownership change that triggered Sections 382 and 383, which may limit our ability to utilize net operating loss and tax credit carryforwards.
	Tax years from 2011 through 2014 are currently open for audit by federal and state taxing authorities. We are currently under income tax examination for federal income tax purposes for the year ended December 31, 2012. As of December 31, 2014, we do not anticipate any material adjustments resulting from the tax examination.
	Changes for unrecognized tax benefits for the periods presented are as follows (in thousands):
	Balance at January 1, 2012	$	1,225
	Gross increases—prior period tax positions		30
	Balance at December 31, 2012	$	1,255
	Gross increases—prior and current period tax positions		3,868
	Balance at December 31, 2013	$	5,123
	Gross increases—current period tax positions		1,946
	Gross decreases—prior period tax positions		(576	)
	Balance at December 31, 2014	$	6,493
	We do not anticipate that the amount of existing unrecognized tax benefits will significantly increase or decrease within the next 12 months. Accrued interest and penalties related to unrecognized tax benefits are recorded as income tax expense and are zero.

Shareholders_Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Shareholders' Equity	Note 9. Shareholders’ Equity
	Our board of directors has the authority to fix and determine and to amend the number of shares of any series of preferred stock that is wholly unissued or to be established and to fix and determine and to amend the designation, preferences, voting powers and limitations, and the relative, participating, optional or other rights, of any series of shares of preferred stock that is wholly unissued or to be established, subject in each case to certain approval rights of holders of our outstanding Class B common stock. There was no preferred stock issued and outstanding as of December 31, 2014 or 2013.
	Our Class A common stock has no preferences or privileges and is not redeemable. Holders of Class A common stock are entitled to one vote for each share.
	Our Class B common stock has no preferences or privileges and is not redeemable. At any time after the date of issuance, each share of Class B common stock, at the option of the holder, may be converted into one share of Class A common stock, or automatically converted upon the affirmative vote by or written consent of holders of a majority of the shares of the Class B common stock. During the year ended December 31, 2014, 251,445 shares of Class B common stock were converted into Class A common stock at the option of the holders. Holders of Class B common stock are entitled to 10 votes for each share.
	In September 2012, we sold 3,844,818 shares of our Class A common stock, including 419,818 shares of our Class A common stock pursuant to the underwriters’ option to purchase additional shares, and certain shareholders sold 575,000 shares of our Class A common stock, at a price of $43.00 per share. We received net proceeds of $156.7 million after deducting underwriting discounts and commissions and offering expenses payable by us. We received no proceeds from the sale of our Class A common stock by the selling shareholders.
	In August 2013, we sold 3,253,522 shares of our Class A common stock, including 753,522 shares of our Class A common stock pursuant to the underwriters’ option to purchase additional shares, and certain shareholders sold 2,523,486 shares of our Class A common stock, at a price of $82.00 per share. We received net proceeds of $253.9 million after deducting underwriting discounts and commissions and offering expenses payable by us. We received no proceeds from the sale of our Class A common stock by the selling shareholders.
	The following shares of Class A common stock have been reserved for future issuance as of the dates presented:
		December 31,		December 31,
		2014		2013
	Class A common option awards outstanding		5,799,764		5,156,706
	Class A common stock available for grant under equity plan		672,606		1,144,762
	Restricted stock units outstanding		125,602		121,123
	Shares issuable upon conversion of outstanding Class B common stock		6,217,447		6,468,892
	Total		12,815,419		12,891,483

ShareBased_Awards

Share-Based Awards	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Awards	Note 10. Share-Based Awards
	On July 19, 2011, our 2011 Incentive Plan (as amended and/or restated from time to time, the “2011 Plan”) became effective and serves as the successor to our 2005 Equity Incentive Plan (the “2005 Plan”). Under the 2011 Plan 3,800,000 shares of Class A common stock are reserved for issuance. The number of shares of Class A common stock available for issuance under the 2011 Plan automatically increases on the first day of each of our fiscal years beginning in 2013 by a number of shares equal to the least of (a) 3.5% of our outstanding Class A common stock and Class B common stock on a fully diluted basis as of the end of our immediately preceding fiscal year, (b) 3,500,000 shares, and (c) a lesser amount determined by our board of directors; provided, however, that any shares from any increases in previous years that are not actually issued will continue to be available for issuance under the 2011 Plan. In addition, shares previously available for grant under the 2005 Plan, but not issued or subject to outstanding awards under the 2005 Plan as of July 19, 2011, and shares subject to outstanding awards under the 2005 Plan that subsequently cease to be subject to such awards (other than by reason of exercise of the awards) are available for grant under the 2011 Plan. The 2011 Plan is administered by the compensation committee of the board of directors. Under the terms of the 2011 Plan, the compensation committee may grant equity awards, including incentive stock options, nonqualified stock options, restricted stock, restricted stock units or restricted units to employees, officers, directors, consultants, agents, advisors and independent contractors. The compensation committee has also authorized certain senior executive officers to grant equity awards under the 2011 Plan, within limits prescribed by the compensation committee.
	Option Awards
	All option awards granted from inception through December 31, 2014 are nonqualified stock options, with the exception of substituted incentive stock options for 15,143 shares of Zillow’s Class A common stock that were granted in connection with the December 14, 2012 acquisition of HotPads, Inc. Option awards under the 2011 Plan are granted with an exercise price per share not less than 100% of the fair market value of our Class A common stock on the date of grant, with the exception of substituted option awards granted in connection with acquisitions, and are exercisable at such times and under such conditions as determined by the compensation committee. Under the 2011 Plan, the maximum term of an option award is ten years from the date of grant. Any portion of an option award that is not vested and exercisable on the date of a participant’s termination of service expires on such date. Employees generally forfeit their rights to exercise vested option awards after 3 months following their termination of employment or 12 months in the event of termination by reason of death, disability or retirement. Option awards granted under the 2011 Plan are typically granted with seven-year terms and typically vest 25% after 12 months and ratably thereafter over the next 36 months, except for option awards granted under the Stock Option Grant Program for Nonemployee Directors (“Nonemployee Director Awards”), which are fully vested and exercisable on the date of grant, and except for certain option awards that were granted to our chief executive officer in December 2012 and January 2013.
	The following table summarizes option award activity for the year ended December 31, 2014:
		Shares			Number of			Weighted-		Weighted-		Aggregate
		Available			Shares			Average		Average		Intrinsic
		for Grant			Subject to			Exercise		Remaining		Value
					Existing			Price Per		Contractual
					Option			Share		Life (Years)
					Awards
	Outstanding at January 1, 2014		1,513,264			5,156,706		$	27.09		5.43	$	283,008,505
	Authorized increase in plan shares		1,563,827			—			—
	Granted		(2,219,458	)		2,219,458			97.06
	Exercised		—			(1,323,509	)		18.08
	Forfeited or cancelled		252,891			(252,891	)		62.76
	Outstanding at December 31, 2014		1,110,524			5,799,764			54.37		5.32		311,040,401
	Vested and exercisable at December 31, 2014					1,685,583			21.95		3.77		141,486,370
	The shares available for grant in the above table exclude option awards for an aggregate of 25,385 shares that were granted in 2013 in substitution of option awards previously granted by StreetEasy, Inc. Pursuant to the terms of the 2011 Plan, such substituted option awards do not reduce the number of shares available for future issuance under the 2011 Plan. As of December 31, 2014, the shares available for grant in the above table do not include 139,002 shares of restricted stock and 298,916 restricted stock units granted under our 2011 Plan. Aggregate intrinsic value represents the difference between the fair market value of our Class A common stock and the exercise price of outstanding, in-the-money options.
	As of December 31, 2014, there was a total of $90.7 million in unrecognized compensation cost related to unvested option awards, which is expected to be recognized over a weighted-average period of 3.1 years. The total intrinsic value of option awards exercised during the years ended December 31, 2014, 2013 and 2012 was $124.0 million, $114.4 million and $49.7 million, respectively.
	The fair value of option awards granted, excluding Nonemployee Director Awards and certain option awards granted to the Company’s chief executive officer in December 2012 and January 2013, is estimated at the date of grant using the Black-Scholes-Merton option-pricing model, assuming no dividends and with the following assumptions for the periods presented:
		Year Ended December 31,
		2014		2013	2012
	Expected volatility	53% – 57%		50% – 54%	49% – 52%
	Expected dividend yields	—		—	—
	Average risk-free interest rate	1.37% – 1.55%		0.70% – 1.27%	0.53% – 0.76%
	Weighted-average expected life	4.58 years		4.58 years	4.58 years
	Weighted-average fair value of option awards granted	$44.34		$21.26	$13.79
	In March 2014, option awards for an aggregate of 23,010 shares of our Class A common stock were granted as Nonemployee Director Awards. The fair value of option awards granted for the Nonemployee Director Awards, $32.60 per share, is estimated at the date of grant using the Black-Scholes-Merton option-pricing model, assuming no dividends, expected volatility of 54%, a risk-free interest rate of 0.69%, and a weighted-average expected life of 3.5 years. During the year ended December 31, 2014, share-based compensation expense recognized in our statement of operations related to the March 2014 Nonemployee Director Awards was $0.8 million, and is included in general and administrative expenses.
	On January 24, 2013, an option award for 500,000 shares of our Class A common stock was granted to the Company’s chief executive officer. The fair value of the option award, $19.00 per share, is estimated at the date of grant using the Black-Scholes-Merton option-pricing model, assuming no dividends, expected volatility of 51%, a risk-free interest rate of 0.70% and a weighted-average expected life of 7.3 years. In December 2012, an option award for 500,000 shares of our Class A common stock was granted to the Company’s chief executive officer. The fair value of the option award, $12.23 per share, is estimated at the date of grant using the Black-Scholes-Merton option-pricing model, assuming no dividends, expected volatility of 49%, a risk-free interest rate of 0.60%, and a weighted-average expected life of 5.0 years.
	The fair value of option awards vested for the years ended December 31, 2014, 2013 and 2012 was $1.8 million, $1.2 million and $0.8 million, respectively.
	The following table summarizes information about option awards outstanding and option awards vested and exercisable as of December 31, 2014:
		Option Awards Outstanding								Option Awards Vested and Exercisable
	Exercise Price or Range	Number			Weighted-			Weighted-		Number		Weighted-
		Outstanding			Average			Average		Exercisable		Average Exercise
					Remaining			Exercise				Price
					Contractual Life			Price
					(Years)
	$1.95—$19.84		888,955			2.8		$	3.87		790,891	$	3.78
	$24.80—$29.69		582,168			4.79			28.19		170,611		28.07
	$30.46—$36.30		545,314			4.14			31.08		295,518		31.03
	$36.36—$38.60		1,268,964			6.23			36.43		273,343		36.5
	$38.97—$81.97		343,766			5.42			60.99		106,943		54.31
	$82.05		1,019,380			6.01			82.05		—		—
	$82.74—$107.94		593,028			6.29			95.2		48,277		88.38
	$109.93—$144.07		530,891			6.65			126.56		—		—
	$144.94		21,478			6.65			144.94		—		—
	$160.32		5,820			6.57			160.32		—		—
	Total		5,799,764			5.32			54.37		1,685,583		21.95
	Restricted Stock Awards
	The following table summarizes restricted stock award activity for the year ended December 31, 2014:
		Shares of			Weighted-
		Restricted Stock			Average Grant-
					Date Fair
					Value
	Unvested outstanding at January 1, 2014		230,127		$	30.43
	Granted		3,255			80.91
	Vested		(146,547	)		30.48
	Forfeited or cancelled		—			—
	Unvested outstanding at December 31, 2014		86,835			32.25
	The total fair value of shares of restricted stock awards vested for the years ended December 31, 2014, 2013 and 2012 was $4.5 million, $3.4 million and $1.0 million, respectively.
	The fair value of the outstanding restricted stock awards will be recorded as share-based compensation expense over the vesting period. As of December 31, 2014, there was $2.5 million of total unrecognized compensation cost related to restricted stock awards, which is expected to be recognized over a weighted-average period of 1.1 years.
	Restricted Stock Units
	The following table summarizes activity for restricted stock units for the year ended December 31, 2014:
	Restricted			Weighted-
	Stock			Average Grant-
	Units			Date Fair
				Value
Unvested outstanding at January 1, 2014		121,123		$	64.07
Granted		102,264			102.95
Vested		(64,935	)		76.28
Forfeited or cancelled		(32,850	)		72.4
Unvested outstanding at December 31, 2014		125,602			85.67
In April 2014, pursuant to the terms of an Amended and Restated Executive Employment Agreement and a Restricted Stock Unit Award Notice and Restricted Stock Unit Award Agreement entered into between Zillow and an employee, Zillow granted to the employee restricted stock units for 59,320 shares of our Class A common stock, which vest quarterly over four years beginning on the vesting commencement date of March 26, 2014, subject to the recipient’s continued full-time employment or service to Zillow. In the event of termination of service or employment by Zillow without cause or upon the resignation by such employee for good reason, the employee will receive 24 months’ accelerated vesting of the restricted stock units, except that in the event of such a termination in connection with a change in control, the restricted stock units will become fully vested. The employee will be entitled to receive one share of Zillow’s Class A common stock for each then outstanding unit that becomes vested. The grant date fair value of the restricted stock units is approximately $5.4 million.
In June 2014, pursuant to the terms of Restricted Stock Unit Award Notices and Restricted Stock Unit Award Agreements entered into between Zillow and certain employees, Zillow granted to the employees restricted stock units for a total of 24,880 shares of our Class A common stock, which vest ratably after each six-month period over two years beginning on the vesting commencement date of June 3, 2014, subject to the recipients’ continued full-time employment or service to Zillow. In the event of termination of service of employment by Zillow without cause, 50% of the then unvested restricted stock units will become vested units, and the recipient will be entitled to receive one share of Zillow’s Class A common stock for each then outstanding unit. The grant date fair value of the restricted stock units is approximately $3.2 million.
The total fair value of vested restricted stock units was $7.4 million, $10.8 million and $0 million, respectively, for the years ended December 31, 2014, 2013 and 2012.
The fair value of the outstanding restricted stock units will be recorded as share-based compensation expense over the vesting period. As of December 31, 2014, there was $10.8 million of total unrecognized compensation cost related to restricted stock units, which is expected to be recognized over a weighted-average period of 2.57 years.
Share-Based Compensation Expense
The following table presents the effects of share-based compensation in our statements of operations during the periods presented (in thousands):
	Year Ended December 31,
	2014			2013			2012
Cost of revenue	$	1,844		$	737		$	380
Sales and marketing		7,320			10,969			2,433
Technology and development		11,681			4,660			1,886
General and administrative		13,240			7,070			1,912
	$	34,085		$	23,436		$	6,611

Net_Income_Loss_Per_Share

Net Income (Loss) Per Share	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Net Income (Loss) Per Share	Note 11. Net Income (Loss) Per Share
	Basic net income (loss) per share is computed by dividing net income (loss) by the weighted-average number of common shares (including Class A common stock and Class B common stock) outstanding during the period. In the calculation of basic net income (loss) per share, undistributed earnings are allocated assuming all earnings during the period were distributed.
	Diluted net income (loss) per share is computed by dividing net income (loss) by the weighted-average number of common shares (including Class A common stock and Class B common stock) outstanding during the period and potentially dilutive Class A common stock equivalents, except in cases where the effect of the Class A common stock equivalent would be antidilutive. Potential Class A common stock equivalents consist of Class A common stock issuable upon exercise of option awards and Class A common stock underlying unvested restricted stock, restricted stock units and restricted units using the treasury stock method.
	For the periods presented, the following Class A common stock equivalents were included in the computation of diluted net income per share because they had a dilutive impact (in thousands):
		Year Ended December 31,
		2014		2013		2012
	Class A common stock issuable upon the exercise of option awards		—		—		2,469
	Class A common stock underlying unvested restricted stock awards, restricted stock units and restricted units		—		—		46
	Total Class A common stock equivalents		—		—		2,515
	For the periods presented, the following Class A common stock equivalents were excluded from the calculations of diluted net loss per share because their effect would have been antidilutive (in thousands):
		Year Ended December 31,
		2014		2013		2012
	Class A common stock issuable upon the exercise of option awards		2,903		3,179		—
	Class A common stock underlying unvested restricted stock awards, restricted stock units and restricted units		118		171		—
	Total Class A common stock equivalents		3,021		3,350		—
	In the event of liquidation, dissolution, distribution of assets or winding-up of the Company, the holders of all classes of common stock have equal rights to receive all the assets of the Company after the rights of the holders of preferred stock have been satisfied. We have not presented net income (loss) per share under the two-class method for our Class A common stock and Class B common stock because it would be the same for each class due to equal dividend and liquidation rights for each class.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 12. Commitments and Contingencies
	Lease Commitments
	We have various operating leases for office space and equipment. In March 2011, we entered into a lease agreement for office space that houses our corporate headquarters in Seattle, Washington (as amended from time to time, the “Seattle Lease”). Pursuant to the terms of the Seattle Lease, we lease a total of approximately 178,000 square feet, and we are obligated to make escalating monthly lease payments that began in December 2012 and continue through December 2024. In April 2012, we entered into a lease agreement for office space in Irvine, California (as amended from time to time, the “Irvine Lease”). Pursuant to the terms of the Irvine Lease, we lease a total of approximately 60,000 square feet under which we are obligated to make escalating monthly lease payments which began in August 2012 and continue through July 2022. In November 2012, we entered into an operating lease in San Francisco, California for 18,353 square feet under which we are obligated to make escalating monthly lease payments which began in December 2012 and continue through November 2018. In February 2014, we entered into an operating lease in New York, New York (as amended from time to time, the “New York Lease”). Pursuant to the terms of the New York Lease, we lease a total of approximately 39,900 square feet, and we are obligated to make escalating monthly lease payments that began in August 2014 and continue through November 2024. We lease additional office space in Chicago, Illinois, Lincoln, Nebraska, and Vancouver, British Columbia.
	Future minimum payments for all operating leases as of December 31, 2014 are as follows (in thousands):
	2015	$	9,809
	2016		11,464
	2017		15,231
	2018		16,610
	2019		15,114
	All future years		80,270
	Total future minimum lease payments	$	148,498
	Rent expense for the years ended December 31, 2014, 2013 and 2012, was $7.5 million, $4.1 million and $2.6 million, respectively.
	Purchase Commitments
	As of December 31, 2014, we had non-cancelable purchase commitments for content related to our mobile applications and websites totaling $45.8 million. The amounts due for this content as of December 31, 2014 is as follows (in thousands):
	2015	$	13,256
	2016		6,070
	2017		4,701
	2018		5,250
	2019		6,000
	All future years		10,500
	Total future purchase commitments	$	45,777
	Letters of Credit
	We have executed standby letters of credit of $1.8 million in connection with our Seattle Lease and $1.1 million in connection with the operating lease of our New York office. The letters of credit are secured by our investments and are effective until 60 days after the expiration date of the lease.
	Legal Proceedings
	In March 2010, Smarter Agent, LLC (“Smarter Agent”) filed a complaint against us and multiple other defendants, including HotPads, Inc. (“HotPads”), for patent infringement in the U.S. District Court for the District of Delaware. The complaint alleges, among other things, that our mobile technology infringes three patents held by Smarter Agent purporting to cover: a “Global positioning-based real estate database access device and method,” a “Position-based information access device and method” and a “Position-based information access device and method of searching,” and seeks an injunction against the alleged infringing activities and an unspecified award for damages. In November 2010, the U.S. Patent and Trademark Office granted our petition for re-examination of the three patents-in-suit, and, to date, all claims of all three patents remain rejected in the re-examination proceedings, including through appeals to the Patent Trial and Appeal Board. In March 2011, the court granted a stay of the litigation pending the completion of the re-examination proceedings. In addition, in October 2011, Smarter Agent filed a substantially similar complaint against Diverse Solutions, Inc. (“Diverse Solutions”), StreetEasy, and other defendants, for patent infringement in the U.S. District Court for the District of Delaware. On October 31, 2011, we acquired substantially all of the operating assets and certain liabilities of Diverse Solutions, including the Smarter Agent complaint against Diverse Solutions. On December 14, 2012, we acquired HotPads, and took responsibility for the Smarter Agent complaint against HotPads. On August 26, 2013, we acquired StreetEasy, and took responsibility for the Smarter Agent complaint against StreetEasy. We have not recorded an accrual related to these complaints as of December 31, 2014 or 2013, as we do not believe a material loss is probable.
	In September 2010, LendingTree, LLC (“LendingTree”) filed a complaint against us for patent infringement in the U.S. District Court for the Western District of North Carolina. The complaint alleged, among other things, that our website technology infringes two patents purporting to cover a “Method and computer network for coordinating a loan over the internet.” The complaint sought, among other things, a judgment that we infringed certain patents held by LendingTree, an injunction against the alleged infringing activities and an award for damages. We denied the allegations and asserted defenses and counterclaims seeking declarations that we are not infringing the patents and that the patents are invalid. In March 2014, a federal jury found that Zillow does not infringe the patents and that the patents asserted by LendingTree are invalid. In April, 2014, LendingTree filed two motions for judgment as a matter of law and for a new trial, all of which we opposed. In October 2014, the Court issued an order upholding the jury verdict and denying LendingTree’s motions. We have not recorded an accrual related to this complaint as of December 31, 2014 or 2013, as we do not believe a material loss is probable.
	In November 2012, a securities class action lawsuit was filed in the U.S. District Court for the Western District of Washington at Seattle against us and certain of our executive officers seeking unspecified damages. A consolidated amended complaint was filed in June 2013. The complaint purports to state claims for violations of federal securities laws on behalf of a class of those who purchased our common stock between February 15, 2012 and November 6, 2012. The complaint generally alleges, among other things, that during the period between February 15, 2012 and November 6, 2012, we issued materially false and misleading statements regarding our business practices and financial results. In August 2013, we moved to dismiss the lawsuit. On October 20, 2014, the Court issued an order granting our motion to dismiss the consolidated amended complaint with prejudice. Also on October 20, 2014, the Court entered a judgment dismissing the complaint with prejudice. On November 19, 2014, plaintiffs filed a notice of appeal of the October 20, 2014 judgment of dismissal with prejudice. Plaintiffs’ opening appellate brief must be filed by February 27, 2015. We have not recorded an accrual related to this lawsuit as of December 31, 2014 or 2013, as we do not believe a material loss is probable.
	In March 2014, Move, Inc., the National Association of Realtors and three related entities, filed a complaint against us and Errol Samuelson, our Chief Industry Development Officer, in the Superior Court of the State of Washington in King County, alleging, among other things, that Zillow and Mr. Samuelson misappropriated plaintiffs’ trade secrets in connection with Mr. Samuelson joining Zillow in March 2014. The complaint seeks, among other things, an injunction against the alleged misappropriations and Mr. Samuelson working for us, as well as unspecified damages. In April 2014, the court denied the plaintiffs’ motion for a preliminary injunction prohibiting Mr. Samuelson from working for us. Plaintiffs renewed their motion for a preliminary injunction and on September 30, 2014, the court granted that request and entered a preliminary injunction. Zillow filed a motion requesting that the court reconsider that decision, which the court denied. On September 22, 2014, Zillow filed a notice for discretionary review by the Washington Court of Appeals, followed by a motion for discretionary review on October 7, 2014. Samuelson also filed a motion for discretionary review. Zillow’s and Samuelson’s motions for discretionary review were granted on November 19, 2014. On January 26, 2015, the plaintiffs filed a contempt motion for alleged violation of the preliminary injunction, which Zillow and Samuelson opposed. The parties are awariting a ruling from the Superior Court. On February 3, 2015, the parties entered into a stipulation, later adopted by order of the court, that Zillow and Samuelson shall withdraw the appeal and the last of the terms of the preliminary injunction will expire on March 22, 2015. The trial date was also extended to October 26, 2015. We deny the allegations of any wrongdoing and intend to vigorously defend the claims in the lawsuit. We have not recorded an accrual related to these complaints as of December 31, 2014, as we do not believe a material loss is probable.
	In August 2014, four purported class action lawsuits were filed by plaintiffs against Trulia and its directors, Zillow, and Zebra Holdco, Inc. in connection with Zillow’s proposed acquisition of Trulia. One of those purported class actions, captioned Collier et al. v. Trulia, Inc., et al., was brought in the Superior Court of the State of California for the County of San Francisco, however on October 7, 2014, plaintiff in the Collier action filed a new complaint in the Delaware Court of Chancery alleging substantially the same claims and seeking substantially the same relief as the original complaint filed in California. On October 8, 2014, plaintiff in the Collier action filed a request for dismissal of the California case without prejudice. The other three of the purported class action lawsuits, captioned Shue et al. v. Trulia, Inc., et al., Sciabacucci et al. v. Trulia, Inc., et al., and Steinberg et al. v. Trulia, Inc. et al., were brought in the Delaware Court of Chancery. All four lawsuits allege that Trulia’s directors breached their fiduciary duties to Trulia stockholders, and that the other defendants aided and abetted such breaches, by seeking to sell Trulia through an allegedly unfair process and for an unfair price and on unfair terms. All lawsuits seek, among other things, equitable relief that would enjoin the consummation of Zillow’s proposed acquisition of Trulia and attorneys’ fees and costs. The Delaware actions also seek rescission of the Merger Agreement (to the extent it has already been implemented) or rescissory damages and orders directing the defendants to account for alleged damages suffered by the plaintiffs and the purported class as a result of the defendants’ alleged wrongdoing. On September 24, 2014, plaintiff in the Sciabacucci action filed (1) a motion for expedited proceedings, (2) a motion for a preliminary injunction, (3) a request for production of documents from defendants, and (4) notice of depositions. On October 13, 2014, the Delaware Court of Chancery issued an order consolidating all of the Delaware actions into one matter captioned In re Trulia, Inc. Stockholder Litigation and appointed Rigrodsky & Long as lead counsel. On October 13 and 14, 2014, the above-referenced motions were refiled under the consolidated case number. On November 14, 2014, plaintiffs again refiled their motion for a preliminary injunction challenging the proposed acquisition. On November 19, 2014, the parties entered into a Memorandum of Understanding, documenting the agreement-in-principle for the settlement of the consolidated litigation, pursuant to which Trulia agreed to make certain supplemental disclosures in a Form 8-K. The Memorandum of Understanding was filed with the Chancery Court that same day. The parties are currently conducting confirmatory discovery. We have not recorded an accrual related to these lawsuits as of December 31, 2014, as we do not believe a material loss is probable.
	In addition to the matters discussed above, from time to time, we are involved in litigation and claims that arise in the ordinary course of business. Although we cannot be certain of the outcome of any litigation and claims, nor the amount of damages and exposure that we could incur, we currently believe that the final disposition of such matters will not have a material effect on our financial position, results of operations or cash flow. Regardless of the outcome, litigation can have an adverse impact on us because of defense and settlement costs, diversion of management resources and other factors.
	Indemnifications
	In the ordinary course of business, we enter into contractual arrangements under which we agree to provide indemnification of varying scope and terms to business partners and other parties with respect to certain matters, including, but not limited to, losses arising out of the breach of such agreements and out of intellectual property infringement claims made by third parties. In these circumstances, payment may be conditional on the other party making a claim pursuant to the procedures specified in the particular contract. Further, our obligations under these agreements may be limited in terms of time and/or amount, and in some instances, we may have recourse against third parties for certain payments. In addition, we have indemnification agreements with certain of our directors and executive officers that require us, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The terms of such obligations may vary.

Segment_Information_and_Revenu

Segment Information and Revenue	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Segment Information and Revenue	Note 13. Segment Information and Revenue
	We have one reportable segment. Our reportable segment has been identified based on how our chief operating decision-maker manages our business, makes operating decisions and evaluates operating performance. The chief executive officer acts as the chief operating decision-maker and reviews financial and operational information on an entity-wide basis. We have one business activity and there are no segment managers who are held accountable for operations, operating results or plans for levels or components. Accordingly, we have determined that we have a single reporting segment and operating unit structure.
	The chief executive officer reviews information about revenue categories, including marketplace revenue and display revenue. The following table presents our revenue categories during the periods presented (in thousands):
		Year Ended December 31,
		2014		2013		2012
	Marketplace revenue:
	Real estate	$	239,039	$	132,901	$	75,900
	Mortgages		28,203		21,812		10,770
	Total Marketplace revenue		267,242		154,713		86,670
	Display revenue		58,651		42,832		30,180
	Total revenue	$	325,893	$	197,545	$	116,850

Subsequent_Events

Subsequent Events	12 Months Ended
	Dec. 31, 2014
Subsequent Events [Abstract]
Subsequent Events	Note 14. Subsequent Events
	Pursuant to its terms, the Platform Services Agreement, dated as of April 7, 2011, by and between Zillow and Threewide Corporation (“Threewide”) will expire on April 7, 2015. Zillow will not incur any early termination penalties as a result of the agreement’s expiration. Under the terms of the agreement, Threewide granted to Zillow a nonexclusive license to display listings on Zillow’s mobile applications and websites.
	On January 7, 2015, option awards for a total of 650,000 shares of our Class A common stock were granted to certain of the Company’s executive officers. One-sixteenth of the total number of shares subject to the option awards will vest and become exercisable on the first anniversary of the vesting commencement date. An additional 1/192nd of the total number of shares subject to the option awards will vest and become exercisable monthly thereafter over the next three years so that this portion of the award will be vested and exercisable four years from the vesting commencement date. One-sixteenth of the total number of shares subject to the option awards will vest and become exercisable on the two-year anniversary of the vesting commencement date. An additional 1/192nd of the total number of shares subject to the option awards will vest and become exercisable monthly thereafter over the next three years so that this portion of the award will be vested and exercisable five years from the vesting commencement date. One-sixteenth of the total number of shares subject to the option awards will vest and become exercisable on the three-year anniversary of the vesting commencement date. An additional 1/192nd of the total number of shares subject to the option awards will vest and become exercisable monthly thereafter over the next three years so that this portion of the award will be vested and exercisable six years from the vesting commencement date. One-sixteenth of the total number of shares subject to the option awards will vest and become exercisable on the four-year anniversary of the vesting commencement date. An additional 1/192nd of the total number of shares subject to the option awards will vest and become exercisable monthly thereafter over the next three years so that this portion of the award will be vested and exercisable seven years from the vesting commencement date. The option awards have a ten-year term. The option awards are subject to shareholder approval of a share increase under the Company’s Amended and Restated 2011 Incentive Plan, and no portion of the option awards are exercisable until such shareholder approval has been obtained.
	On February 13, 2015, Zillow announced that it received notification from the Federal Trade Commission (“FTC”) that the FTC closed its investigation and would take no action against the proposed acquisition of Trulia (see Note 1). As a result, closing conditions related to the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, have been satisfied. Zillow anticipates that the proposed acquisition will be completed as early as February 17, 2015.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation
	The accompanying consolidated financial statements include Zillow, Inc. and our wholly-owned subsidiary, Zillow (Canada), Inc. All significant intercompany balances and transactions have been eliminated in consolidation. These consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“GAAP”).
Use of Estimates	Use of Estimates
	The preparation of financial statements in conformity with GAAP requires management to make certain estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and the related disclosures at the date of the financial statements, as well as the reported amounts of revenue and expenses during the periods presented. On an ongoing basis, we evaluate our estimates, including those related to revenue recognition, the allowance for doubtful accounts, website development costs, goodwill, recoverability of intangible assets with definite lives and other long-lived assets, and for share-based compensation, among others. To the extent there are material differences between these estimates, judgments, or assumptions and actual results, our financial statements will be affected. In many cases, the accounting treatment of a particular transaction is specifically dictated by GAAP and does not require management’s judgment in its application.
Reclassifications	Reclassifications
	Certain immaterial reclassifications have been made in the consolidated balance sheets and statements of operations to conform data for prior periods to the current format.
Concentrations of Credit Risk	Concentrations of Credit Risk
	Financial instruments, which potentially subject us to concentrations of credit risk, consist primarily of cash and cash equivalents, investments and accounts receivable. We place cash and cash equivalents and investments with major financial institutions, which management assesses to be of high credit quality, in order to limit exposure of our investments.
	Credit risk with respect to accounts receivable is dispersed due to the large number of customers. Further, our credit risk on accounts receivable is mitigated by the relatively short payment terms that we offer. Collateral is not required for accounts receivable. We maintain an allowance for doubtful accounts such that receivables are stated at net realizable value.
Cash and Cash Equivalents	Cash and Cash Equivalents
	Cash includes currency on hand as well as demand deposits with banks or financial institutions. Cash equivalents include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Our cash equivalents include only investments with original maturities of three months or less. We regularly maintain cash in excess of federally insured limits at financial institutions.
Investments	Investments
	Our investments consist of fixed income securities, which include U.S. government agency securities, corporate notes and bonds, municipal securities, commercial paper and certificates of deposit. Securities with maturities greater than three months but less than one year are classified as short-term investments. Securities with maturities greater than one year are classified as long-term investments. Our investments are classified as held-to-maturity and are recorded at amortized cost, as we do not intend to sell the investments, and it is not more likely than not that we will be required to sell these investments prior to maturity. The amortized cost of our investments approximates their fair value.
	We have restricted investment balances primarily used to guarantee various letters of credit (see Note 12). The restricted investment balances are carried at cost, which approximates fair value.
Accounts Receivable and Allowance for Doubtful Accounts	Accounts Receivable and Allowance for Doubtful Accounts
	Accounts receivable are generally due within 30 days and are recorded net of the allowance for doubtful accounts. We consider accounts outstanding longer than the contractual terms past due. We review accounts receivable on a regular basis and estimate an amount of losses for uncollectible accounts based on our historical collections experience, age of the receivable, knowledge of the customer and the condition of the general economy and industry as a whole. We record changes in our estimate to the allowance for doubtful accounts through bad debt expense and relieve the allowance when accounts are ultimately determined to be uncollectible. Bad debt expense is included in general and administrative expenses.
Property and Equipment	Property and Equipment
	Property and equipment is recorded at cost and depreciated using the straight-line method over the estimated useful lives of the related assets. The useful lives are as follows:
	Computer equipment		3 years
	Purchased software		3 years
	Office equipment, furniture and fixtures		5 to 7 years
	Leasehold improvements		Shorter of expected useful life or lease term
	Maintenance and repair costs are charged to expense as incurred. Major improvements, which extend the useful life of the related asset, are capitalized. Upon disposal of a fixed asset, we record a gain or loss based on the differences between the proceeds received and the net book value of the disposed asset.
Website and Software Development Costs	Website and Software Development Costs
	The costs incurred in the preliminary stages of development are expensed as incurred. Once an application has reached the development stage, internal and external costs, if direct and incremental and deemed by management to be significant, are capitalized in property and equipment and amortized on a straight-line basis over their estimated useful lives. Maintenance and enhancement costs, including those costs in the post-implementation stages, are typically expensed as incurred, unless such costs relate to substantial upgrades and enhancements to the website or software that result in added functionality, in which case the costs are capitalized and amortized on a straight-line basis over the estimated useful lives. Amortization expense related to capitalized website and software development costs is included in technology and development expense.
	Capitalized development activities placed in service are amortized over the expected useful lives of those releases, currently estimated at one year. The estimated useful lives of website and software development activities are reviewed frequently and adjusted as appropriate to reflect upcoming development activities that may include significant upgrades and/or enhancements to the existing functionality.
Goodwill	Goodwill
	Goodwill represents the excess of the cost of an acquired business over the fair value of the assets acquired at the date of acquisition. We assess the impairment of goodwill on an annual basis, in our fourth quarter, or whenever events or changes in circumstances indicate that goodwill may be impaired.
	We assess goodwill for possible impairment by first performing a qualitative assessment to determine whether it is more likely than not that the fair value of our reporting unit is less than its carrying amount. If we determine that it is not more likely than not that the fair value of our reporting unit is less than its carrying amount, then the first and second steps of the goodwill impairment test are unnecessary. If we determine that it is more likely than not that the fair value of our reporting unit is less than its carrying amount, we perform the two-step goodwill impairment test. The first step of the goodwill impairment test identifies if there is potential goodwill impairment. If step one indicates that an impairment may exist, a second step is performed to measure the amount of the goodwill impairment, if any. Goodwill impairment exists when the estimated fair value of goodwill is less than its carrying value. If impairment exists, the carrying value of the goodwill is reduced to fair value through an impairment charge recorded in our statements of operations.
Intangible Assets	Intangible Assets
	We purchase and license data content from multiple data providers. This data content consists of U.S. county data about home details (e.g., the number of bedrooms, bathrooms, square footage) and other information relating to the purchase price of homes, both current and historical, as well as imagery, mapping and parcel data that is displayed on our mobile applications and websites. Our home details data not only provides information about a home and its related transactions which is displayed on our mobile applications and websites, but is also used in our proprietary valuation algorithms to produce Zestimates, Rent Zestimates and Zillow Home Value Indexes. License agreement terms vary by vendor. In some instances, we retain perpetual rights to this information after the contract ends; in other instances, the information and data are licensed only during the fixed term of the agreement. Additionally, certain data license agreements provide for uneven payment amounts throughout the life of the contract term.
	We capitalize payments made to third parties for data licenses that we expect to provide future economic benefit through the recovery of the costs of these arrangements via the generation of our revenue and margins. For data license contracts that include uneven payment amounts, we capitalize the payments as they are made as an intangible asset and amortize the total contract value over the estimated useful life. For contracts in which we have perpetual rights to the data, the total contract value is amortized on a straight-line basis over the life of the contract plus two years, which is equivalent to the estimated useful life of the asset. For contracts in which we do not have access to the data beyond the contractual term, the total contract value is amortized on a straight line basis over the term of the contract. We evaluate data content contracts for potential capitalization at the inception of the arrangement as well as each time periodic payments to third parties are made.
	The amortization period for the capitalized purchased content is based on our best estimate of the useful life of the asset, which ranges from two to nine years. The determination of the useful life includes consideration of a variety of factors including, but not limited to, our assessment of the expected use of the asset and contractual provisions that may limit the useful life, as well as an assessment of when the data is expected to become obsolete based on our estimates of the diminishing value of the data over time. We evaluate the useful life of the capitalized purchased data content each reporting period to determine whether events and circumstances warrant a revision to the remaining useful life. If we determine the estimate of the asset’s useful life requires modification, the carrying amount of the asset is amortized prospectively over the revised useful life. The capitalized purchased data content is amortized on a straight-line basis as the pattern of delivery of the economic benefits of the data cannot reliably be determined because we do not have the ability to reliably predict future traffic to our websites and mobile applications.
	Under certain other data agreements, the underlying data is obtained on a subscription basis with consistent monthly recurring payment terms over the contractual period. Upon the expiration of such arrangements, we no longer have the right to access the related data, and therefore, the costs incurred under such contracts are not capitalized and are expensed as payments are made. We would immediately lose rights to data under these arrangements if we were to cancel the subscription and/or cease making payments under the subscription arrangements.
	We also have intangible assets for developed technology, customer relationships and trademarks which we recorded in connection with acquisitions. These intangible assets are amortized over the estimated useful life of the asset.
	Recoverability of Intangible Assets with Definite Lives and Other Long-Lived Assets
	We evaluate intangible assets and other long-lived assets for impairment whenever events or circumstances indicate that they may not be recoverable. Recoverability is measured by comparing the carrying amount of an asset group to future undiscounted net cash flows expected to be generated. We group assets for purposes of such review at the lowest level for which identifiable cash flows of the asset group are largely independent of the cash flows of the other groups of assets and liabilities. If this comparison indicates impairment, the amount of impairment to be recognized is calculated as the difference between the carrying value and the fair value of the asset group.
Deferred Revenue	Deferred Revenue
	Deferred revenue consists of prepaid advertising fees received or billed in advance of the delivery or completion of the services, and for amounts received in instances when revenue recognition criteria have not been met. Deferred revenue is recognized when the services are provided and all revenue recognition criteria have been met.
Deferred Rent	Deferred Rent
	For our operating leases, we recognize rent expense on a straight-line basis over the terms of the leases and, accordingly, we record the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. Landlord-funded leasehold improvements are also recorded as deferred rent liabilities and are amortized as a reduction of rent expense over the non-cancelable term of the related operating lease.
Revenue Recognition	Revenue Recognition
	In general, we recognize revenue when (i) persuasive evidence of an arrangement exists, (ii) delivery has occurred or services have been rendered to the customer, (iii) the fee is fixed or determinable, and (iv) collectability is reasonably assured. We consider a signed agreement, a binding insertion order or other similar documentation reflecting the terms and conditions under which products or services will be provided to be persuasive evidence of an arrangement. Collectability is assessed based on a number of factors, including payment history and the creditworthiness of a customer. If it is determined that collection is not reasonably assured, revenue is not recognized until collection becomes reasonably assured, which is generally upon receipt of cash.
	We generate revenue from the sale of advertising services and our suite of tools to businesses and professionals primarily associated with the real estate and mortgage industries. These professionals include local real estate professionals, mortgage professionals and brand advertisers. Our two revenue categories are marketplace revenue and display revenue. Incremental direct costs incurred related to the acquisition or origination of a customer contract in a transaction that results in the deferral of revenue are expensed as incurred.
	Marketplace Revenue. Marketplace revenue consists of real estate revenue and mortgages revenue. Real estate revenue primarily includes revenue from impressions delivered under our Premier Agent program, as well as revenue generated by Zillow Rentals. Mortgages revenue primarily includes advertising sold to mortgage lenders on a cost-per-click, or CPC, basis, related to Zillow Mortgages, as well as revenue generated by Mortech, which provides subscription-based mortgage software solutions, including a product and pricing engine and lead management platform, for which we recognize revenue on a straight-line basis during the contractual period over which the services are delivered.
	Zillow’s Premier Agent program offers a suite of marketing and business technology solutions to help real estate agents grow their businesses and personal brands. The Premier Agent program allows agents to select products and services that they can tailor to meet their business and advertising needs. The program has three tiers of participation including Premier Platinum, our flagship product, as well as Premier Gold and Premier Silver, to meet different marketing and business needs of a broad range of agents. All tiers of Premier Agents receive access to a dashboard portal on our website that provides individualized program performance analytics, as well as our personalized website service, and our free customer relationship management, or CRM, tool that captures detailed information about each contact made with a Premier Agent through our mobile and web platforms. Our Premier Gold product also includes featured listings whereby the agent’s listings will appear at the top of search results on our mobile and web platforms. Our Premier Platinum product includes the dashboard portal on our website, our personalized website service, our CRM tool, featured listings, and inclusion on our buyer’s agent list, whereby the agent appears as the agent to contact for listings in the purchased zip code.
	We charge for our Platinum Premier Agent product based on the number of impressions delivered on our buyer’s agent list in zip codes purchased and a contracted maximum cost per impression. Our Platinum Premier Agent product includes multiple deliverables which are accounted for as a single unit of accounting, as the delivery or performance of the undelivered elements is based on traffic to our mobile applications and websites. We recognize revenue related to our impression-based Platinum Premier Agent product based on the lesser of (i) the actual number of impressions delivered on our buyer’s agent list during the period multiplied by the contracted maximum cost per impression, or (ii) the contractual maximum spend on a straight-line basis during the contractual period over which the services are delivered, typically over a period of six months or twelve months and then month-to-month thereafter.
	We charge a fixed subscription fee for our Premier Gold and Premier Silver subscription products. Subscription advertising revenue for our Premier Gold and Premier Silver subscription products is recognized on a straight-line basis during the contractual period over which the services are delivered, typically over a period of six months and then month-to-month thereafter.
	In Zillow Mortgages, participating qualified mortgage lenders make a prepayment to gain access to consumers interested in connecting with mortgage professionals. Consumers who request rates for mortgage loans in Zillow Mortgages are presented with personalized lender quotes from participating lenders. We only charge mortgage lenders a fee when users click for more information regarding a mortgage loan quote. Mortgage lenders who exhaust their initial prepayment can then prepay additional funds to continue to participate in the marketplace. We recognize revenue when a user clicks on a mortgage advertisement or to obtain additional information about a mortgage loan quote.
	Display Revenue. Display revenue primarily consists of graphical mobile and web advertising sold on a cost per thousand impressions, or CPM basis, to advertisers primarily in the real estate industry, including real estate brokerages, home builders, mortgage lenders and home services providers. Our advertising customers also include telecommunications, automotive, insurance and consumer products companies. We recognize display revenue as impressions are delivered to users interacting with our mobile applications or websites.
	There were no customers that generated 10% or more of our total revenue in the years ended December 31, 2014, 2013 or 2012.
Cost of Revenue	Cost of Revenue
	Our cost of revenue consists of expenses related to operating our mobile applications and websites, including associated headcount expenses, such as salaries and benefits and share-based compensation expense and bonuses. Cost of revenue also includes credit card fees, ad serving costs paid to third parties, revenue-sharing costs related to our commercial business relationships, and data center operations costs.
Research and Development	Research and Development
	Research and development costs are expensed as incurred. For the years ended December 31, 2014, 2013 and 2012, expenses attributable to research and development for our business totaled $72.9 million, $41.7 million and $22.0 million, respectively. Research and development costs are recorded in technology and development expenses.
Other Income	Other Income
	Other income consists primarily of interest income earned on our cash, cash equivalents and investments.
Share-Based Compensation	Share-Based Compensation
	We measure compensation expense for all share-based awards at fair value on the date of grant and recognize compensation expense over the service period on a straight-line basis for awards expected to vest.
	We use the Black-Scholes-Merton option-pricing model to determine the fair value for option awards. In valuing our option awards, we make assumptions about risk-free interest rates, dividend yields, volatility, and weighted-average expected lives, including estimated forfeiture rates. Risk-free interest rates are derived from U.S. Treasury securities as of the option award grant date. Expected dividend yield is based on our historical dividend payments, which have been zero to date. The expected volatility for our Class A common stock is estimated using a combination of our historical volatility and the published historical volatilities of industry peers in the online publishing market representing the verticals in which we operate. We estimate the weighted-average expected life of the option awards as the average of the option vesting schedule and the term of the award, since we do not have sufficient historical exercise data to provide a reasonable basis upon which to estimate expected term due to the limited period of time share-based awards have been exercisable. The term of the award is estimated using the simplified method, as awards are plain vanilla option awards. Forfeiture rates are estimated using historical actual forfeiture trends as well as our judgment of future forfeitures. These rates are evaluated at least quarterly and any change in compensation expense is recognized in the period of the change. The estimation of option awards that will ultimately vest requires judgment, and to the extent actual results or updated estimates differ from our current estimates, such amounts will be recorded as a cumulative adjustment in the period the estimates are revised. We consider many factors when estimating expected forfeitures, including employee class and historical experience. Actual results, and future changes in estimates, may differ substantially from management’s current estimates.
	For issuances of restricted stock awards, restricted stock units and restricted units, we determine the fair value of the award based on the market value of our Class A common stock at the date of grant.
Advertising Costs	Advertising Costs
	Advertising costs are expensed as incurred. For the years ended December 31, 2014, 2013 and 2012, expenses attributable to advertising totaled $73.1 million, $38.7 million and $11.1 million, respectively. Advertising costs are recorded in sales and marketing expenses.
Income Taxes	Income Taxes
	We use the asset and liability approach for accounting and reporting income taxes, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the financial statement and tax bases of assets and liabilities at the applicable enacted tax rates. A valuation allowance against deferred tax assets would be established if, based on the weight of available evidence, it is more likely than not (a likelihood of more than 50%) that some or all of the deferred tax assets are not expected to be realized.
	We establish reserves for tax-related uncertainties based on estimates of whether, and the extent to which, additional taxes will be due. We adjust these reserves in light of changing facts and circumstances, such as the closing of a tax audit, new tax legislation or the change of an estimate. To the extent that the final tax outcome of these matters is different than the amounts recorded, such differences will affect the provision for income taxes in the period in which such determination is made.
Recently Issued Accounting Standards	Recently Issued Accounting Standards
	In August 2014, the Financial Accounting Standards Board (“FASB”) issued guidance on the disclosure of uncertainties about an entity’s ability to continue as a going concern. This standard provides guidance about management’s responsibility to evaluate whether there is substantial doubt about an entity’s ability to continue as a going concern and to provide related footnote disclosures. The guidance is effective for annual reporting periods ending after December 15, 2016, and early adoption is permitted. We expect to adopt this guidance on January 1, 2017. We do not expect the adoption of this guidance to have any impact on our financial position, results of operations or cash flows.
	In May 2014, the FASB issued guidance on revenue recognition. This guidance provides that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This guidance also requires more detailed disclosures to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. This guidance is effective for interim and annual reporting periods beginning after December 15, 2016, early adoption is not permitted, and must be applied retrospectively or modified retrospectively. We expect to adopt this guidance on January 1, 2017. We have not yet determined the impact the adoption of this guidance will have on our financial position, results of operations or cash flows, if any.
Fair Value	Accounting standards define fair value as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market in an orderly transaction between market participants on the measurement date. The standards also establish a fair value hierarchy, which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. There are three levels of inputs that may be used to measure fair value:
		•		Level 1—Quoted prices in active markets for identical assets or liabilities.
		•		Level 2—Assets and liabilities valued based on observable market data for similar instruments, such as quoted prices for similar assets or liabilities.
		•		Level 3—Unobservable inputs that are supported by little or no market activity; instruments valued based on the best available data, some of which is internally developed, and considers risk premiums that a market participant would require.
	We applied the following methods and assumptions in estimating our fair value measurements:
	Cash equivalents—Cash equivalents are comprised of highly liquid investments with original maturities of less than three months. The fair value measurement of these assets is based on quoted market prices in active markets and these assets are recorded at fair value.
	Short-term and long-term investments—Our investments consist of fixed income securities, which include U.S. government agency securities, corporate notes and bonds, municipal securities, commercial paper and certificates of deposit. The fair value measurement of these assets is based on observable market-based inputs or inputs that are derived principally from or corroborated by observable market data by correlation or other means.
Net Income (Loss) Per Share	Basic net income (loss) per share is computed by dividing net income (loss) by the weighted-average number of common shares (including Class A common stock and Class B common stock) outstanding during the period. In the calculation of basic net income (loss) per share, undistributed earnings are allocated assuming all earnings during the period were distributed.
	Diluted net income (loss) per share is computed by dividing net income (loss) by the weighted-average number of common shares (including Class A common stock and Class B common stock) outstanding during the period and potentially dilutive Class A common stock equivalents, except in cases where the effect of the Class A common stock equivalent would be antidilutive. Potential Class A common stock equivalents consist of Class A common stock issuable upon exercise of option awards and Class A common stock underlying unvested restricted stock, restricted stock units and restricted units using the treasury stock method.
Segment Information and Revenue	We have one reportable segment. Our reportable segment has been identified based on how our chief operating decision-maker manages our business, makes operating decisions and evaluates operating performance. The chief executive officer acts as the chief operating decision-maker and reviews financial and operational information on an entity-wide basis. We have one business activity and there are no segment managers who are held accountable for operations, operating results or plans for levels or components. Accordingly, we have determined that we have a single reporting segment and operating unit structure.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Useful Lives	The useful lives are as follows:
	Computer equipment	3 years
	Purchased software	3 years
	Office equipment, furniture and fixtures	5 to 7 years
	Leasehold improvements	Shorter of expected useful life or lease term

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value Measu of Cash Equivalents and Investments	The following tables present the fair value of cash equivalents and investments as of the dates presented (in thousands):
		December 31, 2014
		Total		Level 1		Level 2
	Cash equivalents:
	Money market funds	$	98,645	$	98,645	$	—
	Foreign government securities		9,035		—		9,035
	Certificates of deposit		2,975		—		2,975
	Short-term investments:
	U.S government agency securities		118,342		118,342		—
	Corporate notes and bonds		78,746		—		78,746
	Municipal securities		26,256		—		26,256
	Foreign government securities		8,570		—		8,570
	Commercial paper		7,987		—		7,987
	Certificates of deposit		6,928		—		6,928
	Long-term investments:
	U.S government agency securities		63,515		63,515		—
	Municipal securities		12,917		—		12,917
	Corporate notes and bonds		6,694		—		6,694
	Certificates of deposit		200		—		200
	Total	$	440,810	$	280,502	$	160,308
		31-Dec-13
		Total		Level 1		Level 2
	Cash equivalents:
	Money market funds	$	184,941	$	184,941	$	—
	U.S government agency securities		3,306		3,306		—
	Short-term investments:
	U.S government agency securities		78,448		78,448		—
	Commercial paper		3,998		—		3,998
	Corporate notes and bonds		11,085		—		11,085
	Long-term investments:
	U.S government agency securities		112,623		112,623		—
	Corporate notes and bonds		29,812		—		29,812
	Total	$	424,213	$	379,318	$	44,895

Accounts_Receivable_net_Tables

Accounts Receivable, net (Tables)	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Accounts Receivable	The following table presents the detail of accounts receivable as of the dates presented (in thousands):
		December 31,
		2014			2013
	Accounts receivable	$	17,373		$	13,793
	Unbilled accounts receivable		4,122			3,291
	Less: allowance for doubtful accounts		(2,811	)		(1,850	)
	Accounts receivable, net	$	18,684		$	15,234
Allowance for Doubtful Accounts	The following table presents the changes in the allowance for doubtful accounts for the periods presented (in thousands):
		Year Ended December 31,
		2014			2013			2012
	Allowance for doubtful accounts:
	Balance, beginning of period	$	1,850		$	965		$	683
	Additions charged to expense		2,529			1,907			1,227
	Less: write-offs, net of recoveries and other adjustments		(1,568	)		(1,022	)		(945	)
	Balance, end of period	$	2,811		$	1,850		$	965

Property_and_Equipment_net_Tab

Property and Equipment, net (Tables)	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Detail of Property and Equipment	The following table presents the detail of property and equipment as of the dates presented (in thousands):
		December 31,
		2014			2013
	Website development costs	$	65,224		$	50,408
	Computer equipment		13,243			8,238
	Leasehold improvements		10,617			7,320
	Software		3,431			1,807
	Construction-in-progress		9,307			3,289
	Office equipment, furniture and fixtures		6,482			3,661
	Property and equipment		108,304			74,723
	Less: accumulated amortization and depreciation		(66,704	)		(47,315	)
	Property and equipment, net	$	41,600		$	27,408

Goodwill_Tables

Goodwill (Tables)	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Change in Goodwill	The following table presents the change in goodwill from December 31, 2013 through December 31, 2014 (in thousands):
	Balance as of December 31, 2013	$	93,213
	Goodwill recorded in connection with an acquisition		3,139
	Balance as of December 31, 2014	$	96,352

Intangible_Assets_Tables

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	The following tables present the detail of intangible assets subject to amortization as of the dates presented (in thousands):
		December 31, 2014
		Cost		Accumulated			Net
				Amortization
	Purchased content	$	24,615	$	(13,904	)	$	10,711
	Developed technology		13,595		(5,322	)		8,274
	Customer relationships		9,225		(3,386	)		5,838
	Trademarks		3,261		(1,327	)		1,934
	Total	$	50,696	$	(23,939	)	$	26,757
		December 31, 2013
		Cost		Accumulated			Net
				Amortization
	Purchased content	$	12,968	$	(8,846	)	$	4,122
	Developed technology		18,835		(4,417	)		14,418
	Customer relationships		9,775		(1,799	)		7,976
	Trademarks		3,261		(628	)		2,633
	Total	$	44,839	$	(15,690	)	$	29,149
Estimated Future Amortization Expense for Intangible Assets	Estimated future amortization expense for intangible assets, including amortization related to future commitments (see Note 12), as of December 31, 2014 is as follows (in thousands):
	2015	$	11,092
	2016		13,514
	2017		10,647
	2018		8,671
	2019		6,900
	All future years		24,128
	Total future amortization expense	$	74,952

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Components of Income Tax Benefit	The following table summarizes the components of our income tax benefit for the periods presented (in thousands):
		Year Ended December 31,
		2014			2013			2012
	Federal	$	—		$	3,783		$	—
	State		—			328			—
	Deferred income tax benefit	$	—		$	4,111		$	—
Reconciliation of Federal Statutory Rate and Effective Tax Rate	The following table presents a reconciliation of the federal statutory rate and our effective tax rate for the periods presented:
		Year Ended December 31,
		2014			2013			2012
	Tax expense at federal statutory rate		(34.0	%)		(34.0	%)		34	%
	State income taxes, net of federal tax benefit		(1.5	%)		(5.8	%)		0	%
	Nondeductible expenses		15.3	%		3.1	%		9.2	%
	Share-based compensation		0.7	%		0.2	%		3.5	%
	Research and development credits		(3.2	%)		(23.3	%)		0	%
	Valuation allowance		22.7	%		35	%		(46.7	%)
	Effective tax rate		0	%		(24.8	%)		0	%
Deferred Tax Assets and Liabilities	The following table presents the significant components of our deferred tax assets and liabilities as of the dates presented (in thousands):
		December 31,
		2014			2013
	Deferred tax assets:
	Federal and state net operating loss carryforwards	$	25,665		$	24,152
	Share-based compensation		12,680			4,467
	Goodwill		1,355			1,776
	Start-up and organizational costs		430			491
	Research and development credits		6,493			5,123
	Accruals and reserves		2,339			901
	Deferred rent		4,248			2,666
	Other		167			749
	Total deferred tax assets		53,377			40,325
	Deferred tax liabilities:
	Website and software development costs		(7,263	)		(4,927	)
	Intangibles		(6,052	)		(6,519	)
	Depreciation and amortization		(2,838	)		(1,579	)
	Net deferred tax assets before valuation allowance		37,224			27,300
	Less: valuation allowance		(37,224	)		(27,300	)
	Net deferred tax assets	$	—		$	—
Changes in Unrecognized Tax Benefits	Changes for unrecognized tax benefits for the periods presented are as follows (in thousands):
	Balance at January 1, 2012	$	1,225
	Gross increases—prior period tax positions		30
	Balance at December 31, 2012	$	1,255
	Gross increases—prior and current period tax positions		3,868
	Balance at December 31, 2013	$	5,123
	Gross increases—current period tax positions		1,946
	Gross decreases—prior period tax positions		(576	)
	Balance at December 31, 2014	$	6,493

Shareholders_Equity_Tables

Shareholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Class A Common Stock Reserved for Future Issuance	The following shares of Class A common stock have been reserved for future issuance as of the dates presented:
		December 31,		December 31,
		2014		2013
	Class A common option awards outstanding		5,799,764		5,156,706
	Class A common stock available for grant under equity plan		672,606		1,144,762
	Restricted stock units outstanding		125,602		121,123
	Shares issuable upon conversion of outstanding Class B common stock		6,217,447		6,468,892
	Total		12,815,419		12,891,483

ShareBased_Awards_Tables

Share-Based Awards (Tables)	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Option Award Activity	The following table summarizes option award activity for the year ended December 31, 2014:
		Shares			Number of			Weighted-		Weighted-		Aggregate
		Available			Shares			Average		Average		Intrinsic
		for Grant			Subject to			Exercise		Remaining		Value
					Existing			Price Per		Contractual
					Option			Share		Life (Years)
					Awards
	Outstanding at January 1, 2014		1,513,264			5,156,706		$	27.09		5.43	$	283,008,505
	Authorized increase in plan shares		1,563,827			—			—
	Granted		(2,219,458	)		2,219,458			97.06
	Exercised		—			(1,323,509	)		18.08
	Forfeited or cancelled		252,891			(252,891	)		62.76
	Outstanding at December 31, 2014		1,110,524			5,799,764			54.37		5.32		311,040,401
	Vested and exercisable at December 31, 2014					1,685,583			21.95		3.77		141,486,370
Fair Value of Option Awards Granted, Excluding Non Employee Director Awards, Estimated at Date of Grant Using Black Scholes Merton Option Pricing Model	The fair value of option awards granted, excluding Nonemployee Director Awards and certain option awards granted to the Company’s chief executive officer in December 2012 and January 2013, is estimated at the date of grant using the Black-Scholes-Merton option-pricing model, assuming no dividends and with the following assumptions for the periods presented:
		Year Ended December 31,
		2014		2013	2012
	Expected volatility	53% – 57%		50% – 54%	49% – 52%
	Expected dividend yields	—		—	—
	Average risk-free interest rate	1.37% – 1.55%		0.70% – 1.27%	0.53% – 0.76%
	Weighted-average expected life	4.58 years		4.58 years	4.58 years
	Weighted-average fair value of option awards granted	$44.34		$21.26	$13.79
Summary of Option Awards Outstanding and Option Awards Vested and Exercisable	The following table summarizes information about option awards outstanding and option awards vested and exercisable as of December 31, 2014:
		Option Awards Outstanding								Option Awards Vested and Exercisable
	Exercise Price or Range	Number			Weighted-			Weighted-		Number		Weighted-
		Outstanding			Average			Average		Exercisable		Average Exercise
					Remaining			Exercise				Price
					Contractual Life			Price
					(Years)
	$1.95—$19.84		888,955			2.8		$	3.87		790,891	$	3.78
	$24.80—$29.69		582,168			4.79			28.19		170,611		28.07
	$30.46—$36.30		545,314			4.14			31.08		295,518		31.03
	$36.36—$38.60		1,268,964			6.23			36.43		273,343		36.5
	$38.97—$81.97		343,766			5.42			60.99		106,943		54.31
	$82.05		1,019,380			6.01			82.05		—		—
	$82.74—$107.94		593,028			6.29			95.2		48,277		88.38
	$109.93—$144.07		530,891			6.65			126.56		—		—
	$144.94		21,478			6.65			144.94		—		—
	$160.32		5,820			6.57			160.32		—		—
	Total		5,799,764			5.32			54.37		1,685,583		21.95
Summary of Restricted Stock Award Activity	The following table summarizes restricted stock award activity for the year ended December 31, 2014:
		Shares of			Weighted-
		Restricted Stock			Average Grant-
					Date Fair
					Value
	Unvested outstanding at January 1, 2014		230,127		$	30.43
	Granted		3,255			80.91
	Vested		(146,547	)		30.48
	Forfeited or cancelled		—			—
	Unvested outstanding at December 31, 2014		86,835			32.25
Summary of Restricted Stock Units Activity	The following table summarizes activity for restricted stock units for the year ended December 31, 2014:
		Restricted			Weighted-
		Stock			Average Grant-
		Units			Date Fair
					Value
	Unvested outstanding at January 1, 2014		121,123		$	64.07
	Granted		102,264			102.95
	Vested		(64,935	)		76.28
	Forfeited or cancelled		(32,850	)		72.4
	Unvested outstanding at December 31, 2014		125,602			85.67
Effects of Share Based Compensation in Statements of Operations	The following table presents the effects of share-based compensation in our statements of operations during the periods presented (in thousands):
		Year Ended December 31,
		2014			2013			2012
	Cost of revenue	$	1,844		$	737		$	380
	Sales and marketing		7,320			10,969			2,433
	Technology and development		11,681			4,660			1,886
	General and administrative		13,240			7,070			1,912
		$	34,085		$	23,436		$	6,611

Net_Income_Loss_Per_Share_Tabl

Net Income (Loss) Per Share (Tables)	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Dilutive Securities Included in Computation of Earnings Per Share	For the periods presented, the following Class A common stock equivalents were included in the computation of diluted net income per share because they had a dilutive impact (in thousands):
		Year Ended December 31,
		2014		2013		2012
	Class A common stock issuable upon the exercise of option awards		—		—		2,469
	Class A common stock underlying unvested restricted stock awards, restricted stock units and restricted units		—		—		46
	Total Class A common stock equivalents		—		—		2,515
Antidilutive Securities Excluded from Computation of Earnings Per Share	For the periods presented, the following Class A common stock equivalents were excluded from the calculations of diluted net loss per share because their effect would have been antidilutive (in thousands):
		Year Ended December 31,
		2014		2013		2012
	Class A common stock issuable upon the exercise of option awards		2,903		3,179		—
	Class A common stock underlying unvested restricted stock awards, restricted stock units and restricted units		118		171		—
	Total Class A common stock equivalents		3,021		3,350		—

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Future Minimum Payments for All Operating Leases	Future minimum payments for all operating leases as of December 31, 2014 are as follows (in thousands):
	2015	$	9,809
	2016		11,464
	2017		15,231
	2018		16,610
	2019		15,114
	All future years		80,270
	Total future minimum lease payments	$	148,498
Purchase Commitments for Content Related to Mobile Applications and Websites	The amounts due for this content as of December 31, 2014 is as follows (in thousands):
	2015	$	13,256
	2016		6,070
	2017		4,701
	2018		5,250
	2019		6,000
	All future years		10,500
	Total future purchase commitments	$	45,777

Segment_Information_and_Revenu1

Segment Information and Revenue (Tables)	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Revenue Categories	The following table presents our revenue categories during the periods presented (in thousands):
		Year Ended December 31,
		2014		2013		2012
	Marketplace revenue:
	Real estate	$	239,039	$	132,901	$	75,900
	Mortgages		28,203		21,812		10,770
	Total Marketplace revenue		267,242		154,713		86,670
	Display revenue		58,651		42,832		30,180
	Total revenue	$	325,893	$	197,545	$	116,850

Organization_and_Description_o1

Organization and Description of Business - Additional Information (Detail) (USD $)	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jul. 28, 2014
Organization And Description Of Business [Line Items]
Agreement date	28-Jul-14
Acquisition-related costs	$21,493,000	$376,000	$1,267,000
Investment banking fees	5,000,000
Trulia Merger | Plan | Class A Common Stock
Organization And Description Of Business [Line Items]
Convertible common stock				0.444
Zillow Merger | Plan | Class A Common Stock
Organization And Description Of Business [Line Items]
Convertible common stock				1
Zillow Merger | Plan | Class B Common Stock
Organization And Description Of Business [Line Items]
Convertible common stock				1
Zillow Merger | Certain circumstances
Organization And Description Of Business [Line Items]
Termination fee payable				69,800,000
Zillow Merger | Additional other certain circumstances
Organization And Description Of Business [Line Items]
Termination fee payable				150,000,000

Useful_Lives_Detail

Useful Lives (Detail)	12 Months Ended
	Dec. 31, 2014
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment	3 years
Purchased software
Property, Plant and Equipment [Line Items]
Property and equipment	3 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment	Shorter of expected useful life or lease term
Minimum | Office equipment, furniture, and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment	5 years
Maximum | Office equipment, furniture, and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment	7 years

Summary_of_Significant_Account3

Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended
	Oct. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
		Customer	Customer	Customer
		Categories
Schedule Of Significant Accounting Policies [Line Items]
Amortization period	2 years
Amortization period, spread on perpetual rights contracts		2 years
Number of revenue categories		2
Number of customers generating more than 10% of total revenue		0	0	0
Research and development costs		$86,406,000	$48,498,000	$26,614,000
Minimum | Customer Concentration Risk | Sales Revenue, Net
Schedule Of Significant Accounting Policies [Line Items]
Percentage of revenue		10.00%	10.00%	10.00%
Technology and Development
Schedule Of Significant Accounting Policies [Line Items]
Research and development costs		72,900,000	41,700,000	22,000,000
Sales and Marketing
Schedule Of Significant Accounting Policies [Line Items]
Advertising expense		$73,100,000	$38,700,000	$11,100,000
Software Development
Schedule Of Significant Accounting Policies [Line Items]
Amortization period		1 year
Purchased Content | Minimum
Schedule Of Significant Accounting Policies [Line Items]
Amortization period		2 years
Purchased Content | Maximum
Schedule Of Significant Accounting Policies [Line Items]
Amortization period		9 years

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Original maturities date of money market funds	Less than three months
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on recurring basis	0	$0
Liabilities measured at fair value	0	$0
Mature in 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment maturity, percentage	74.80%
Investment maturity, year	2015
Mature in 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment maturity, percentage	25.20%
Investment maturity, year	2016

Fair_Value_of_Cash_Equivalents

Fair Value of Cash Equivalents and Investments (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$246,829	$93,531
Long-term investments	83,326	142,435
Total	440,810	424,213
Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	98,645	184,941
Foreign Government Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	9,035
Short-term investments	8,570
Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	2,975
Short-term investments	6,928
Long-term investments	200
US Government Agencies Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		3,306
Short-term investments	118,342	78,448
Long-term investments	63,515	112,623
Corporate Notes and Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	78,746	11,085
Long-term investments	6,694	29,812
Municipal Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	26,256
Long-term investments	12,917
Commercial Paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	7,987	3,998
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	280,502	379,318
Fair Value, Inputs, Level 1 | Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	98,645	184,941
Fair Value, Inputs, Level 1 | US Government Agencies Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		3,306
Short-term investments	118,342	78,448
Long-term investments	63,515	112,623
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	160,308	44,895
Fair Value, Inputs, Level 2 | Foreign Government Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	9,035
Short-term investments	8,570
Fair Value, Inputs, Level 2 | Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	2,975
Short-term investments	6,928
Long-term investments	200
Fair Value, Inputs, Level 2 | Corporate Notes and Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	78,746	11,085
Long-term investments	6,694	29,812
Fair Value, Inputs, Level 2 | Municipal Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	26,256
Long-term investments	12,917
Fair Value, Inputs, Level 2 | Commercial Paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$7,987	$3,998

Accounts_Receivable_Detail

Accounts Receivable (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Receivables [Abstract]
Accounts receivable	$17,373	$13,793
Unbilled accounts receivable	4,122	3,291
Less: allowance for doubtful accounts	-2,811	-1,850	-965	-683
Accounts receivable, net	$18,684	$15,234

Allowance_for_Doubtful_Account

Allowance for Doubtful Accounts (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Allowance for doubtful accounts:
Balance, beginning of period	$1,850	$965	$683
Additions charged to expense	2,529	1,907	1,227
Less: write-offs, net of recoveries and other adjustments	-1,568	-1,022	-945
Balance, end of period	$2,811	$1,850	$965

Detail_of_Property_and_Equipme

Detail of Property and Equipment (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]
Property and equipment	$108,304	$74,723
Less: accumulated amortization and depreciation	-66,704	-47,315
Property and equipment, net	41,600	27,408
Software Development
Property, Plant and Equipment [Line Items]
Property and equipment	65,224	50,408
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment	13,243	8,238
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment	10,617	7,320
Software
Property, Plant and Equipment [Line Items]
Property and equipment	3,431	1,807
Construction-in-progress
Property, Plant and Equipment [Line Items]
Property and equipment	9,307	3,289
Office equipment, furniture, and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment	$6,482	$3,661

Property_and_Equipment_Net_Add

Property and Equipment, Net - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Amortization and depreciation expense related to property and equipment other than website development costs	$6,100,000	$3,500,000	$1,600,000
Capitalization of website development costs	22,200,000	17,300,000	11,500,000
Amortization of website development costs and intangible assets included in technology and development	29,487,000	19,791,000	11,179,000
Technology and Development
Property, Plant and Equipment [Line Items]
Amortization of website development costs and intangible assets included in technology and development	11,100,000	7,600,000	4,300,000
Technology and Development | Software Development
Property, Plant and Equipment [Line Items]
Amortization of website development costs and intangible assets included in technology and development	$18,300,000	$12,200,000	$6,900,000

Change_in_Goodwill_Detail

Change in Goodwill (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Balance as of December 31, 2013	$93,213
Goodwill recorded in connection with an acquisition	3,139
Balance as of December 31, 2014	$96,352

Intangible_Assets_Detail

Intangible Assets (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Finite-Lived Intangible Assets [Line Items]
Cost	$50,696	$44,839
Accumulated Amortization	-23,939	-15,690
Net	26,757	29,149
Purchased Content
Finite-Lived Intangible Assets [Line Items]
Cost	24,615	12,968
Accumulated Amortization	-13,904	-8,846
Net	10,711	4,122
Developed Technology
Finite-Lived Intangible Assets [Line Items]
Cost	13,595	18,835
Accumulated Amortization	-5,322	-4,417
Net	8,274	14,418
Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Cost	9,225	9,775
Accumulated Amortization	-3,386	-1,799
Net	5,838	7,976
Trademarks
Finite-Lived Intangible Assets [Line Items]
Cost	3,261	3,261
Accumulated Amortization	-1,327	-628
Net	$1,934	$2,633

Intangible_Assets_Additional_I

Intangible Assets - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended
	Oct. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Non-cancelable purchase commitment, expiration date	2021-10
Non-cancelable purchase commitment for content	$50,000,000	$45,777,000
Non-cancelable purchase commitment, contractual term	7 years
Estimated useful life of the asset	2 years
Amortization of website development costs and intangible assets included in technology and development		29,487,000	19,791,000	11,179,000
Remaining weighted-average amortization period		6 years 4 months 24 days	4 years 6 months
RentJuice Corporation
Finite-Lived Intangible Assets [Line Items]
Impairment of acquired intangible assets		3,300,000
Technology and Development
Finite-Lived Intangible Assets [Line Items]
Amortization of website development costs and intangible assets included in technology and development		$11,100,000	$7,600,000	$4,300,000

Estimated_Future_Amortization_

Estimated Future Amortization Expense for Intangible Assets (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Goodwill and Intangible Assets Disclosure [Abstract]
2015	$11,092
2016	13,514
2017	10,647
2018	8,671
2019	6,900
All future years	24,128
Total future amortization expense	$74,952

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Income Tax [Line Items]
Income tax liability	$0	$0	$0
Income tax(benefit) expense		-4,111,000
Minimum estimated percentage of deferred tax unrealized	50.00%
Increase/decrease in valuation allowance	9,900,000	5,900,000
Income tax year open for audit	Tax years from 2011 through 2014 are currently open for audit by federal and state taxing authorities.
Unrecognized income tax accrued interest and penalties	0
Research And Development
Schedule Of Income Tax [Line Items]
Net operating loss carryforwards	6,500,000	5,100,000
Tax credit carryforwards expiration year	2025
Change in unrecognized tax benefits period	12 months
Share Based Compensation Liability
Schedule Of Income Tax [Line Items]
Net operating loss carryforwards	286,100,000
Federal
Schedule Of Income Tax [Line Items]
Net operating loss carryforwards	358,600,000	236,500,000
State
Schedule Of Income Tax [Line Items]
Net operating loss carryforwards	$7,200,000	$6,100,000

Components_of_Income_Tax_Benef

Components of Income Tax Benefit (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Federal	$3,783
State	328
Deferred income tax benefit	$4,111

Reconciliation_of_Federal_Stat

Reconciliation of Federal Statutory Rate and Effective Tax rate (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Tax expense at federal statutory rate	-34.00%	-34.00%	34.00%
State income taxes, net of federal tax benefit	-1.50%	-5.80%	0.00%
Nondeductible expenses	15.30%	3.10%	9.20%
Share-based compensation	0.70%	0.20%	3.50%
Research and development credits	-3.20%	-23.30%	0.00%
Valuation allowance	22.70%	35.00%	-46.70%
Effective tax rate	0.00%	-24.80%	0.00%

Deferred_Tax_Assets_and_Liabil

Deferred Tax Assets and Liabilities (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Deferred tax assets:
Federal and state net operating loss carryforwards	$25,665	$24,152
Share-based compensation	12,680	4,467
Goodwill	1,355	1,776
Start-up and organizational costs	430	491
Research and development credits	6,493	5,123
Accruals and reserves	2,339	901
Deferred rent	4,248	2,666
Other	167	749
Total deferred tax assets	53,377	40,325
Deferred tax liabilities:
Website and software development costs	-7,263	-4,927
Intangibles	-6,052	-6,519
Depreciation and amortization	-2,838	-1,579
Net deferred tax assets before valuation allowance	37,224	27,300
Less: valuation allowance	-37,224	-27,300
Net deferred tax assets	$0	$0

Changes_in_Unrecognized_Tax_Be

Changes in Unrecognized Tax Benefits (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Unrecognized tax benefits beginning balance	$5,123	$1,255	$1,225
Gross increases-prior and current-period tax positions	1,946
Gross increases-prior-period tax positions		3,868
Gross increases-current-period tax positions			30
Gross decreases-prior period tax positions	-576
Unrecognized tax benefits ending balance	$6,493	$5,123	$1,255

Shareholders_Equity_Additional

Shareholders' Equity - Additional Information (Detail) (USD $)	1 Months Ended		12 Months Ended
In Millions, except Share data, unless otherwise specified	Aug. 31, 2013	Sep. 30, 2012	Dec. 31, 2014	Dec. 31, 2013
			VotesperShare
Class of Stock [Line Items]
Preferred stock, shares issued			0	0
Preferred stock, shares outstanding			0	0
Net proceeds from issuance of common stock	$253.90	$156.70
Class A Common Stock
Class of Stock [Line Items]
Common stock holders voting right			1
Conversion of common stock conversion ratio			1
Number of common stock issued			0
Issuance of Class A common stock, shares	3,253,522	3,844,818
Class A Common Stock | Over-Allotment Option
Class of Stock [Line Items]
Issuance of Class A common stock, shares	753,522	419,818
Class A Common Stock | Private Placement
Class of Stock [Line Items]
Issuance of Class A common stock, shares	2,523,486	575,000
Class A common stock at an offering price	$82	$43
Class B Common Stock
Class of Stock [Line Items]
Common stock holders voting right			10
Number of common stock converted			251,445

Class_A_Common_Stock_Reserved_

Class A Common Stock Reserved for Future Issuance (Detail)	Dec. 31, 2014	Dec. 31, 2013
Class of Stock [Line Items]
Total	12,815,419	12,891,483
Class B Common Stock
Class of Stock [Line Items]
Shares issuable upon conversion of outstanding Class B common stock	6,217,447	6,468,892
Option Awards
Class of Stock [Line Items]
Class A common option awards outstanding	5,799,764	5,156,706
Class A common stock available for grant under equity plan	672,606	1,144,762
Restricted Stock Units
Class of Stock [Line Items]
Restricted stock units outstanding	125,602	121,123

ShareBased_Awards_Additional_I

Share-Based Awards - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended			1 Months Ended	0 Months Ended	1 Months Ended		9 Months Ended
	Apr. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2014	Jan. 24, 2013	Dec. 31, 2012	Jun. 30, 2014	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, option awards, exercises in period, total intrinsic value		$124,000,000	$114,400,000	$49,700,000
Fair value of option award granted		$44.34	$21.26	$13.79
Weighted-average expected life		4 years 6 months 29 days	4 years 6 months 29 days	4 years 6 months 29 days
Recognized compensation cost		34,085,000	23,436,000	6,611,000
Fair value of option awards vested		1,800,000	1,200,000	800,000
Accelerated vesting period received by employee		24 months
Terms of restricted stock unit award		In the event of termination of service or employment by Zillow without cause or upon the resignation by such employee for good reason, the employee will receive 24 months' accelerated vesting of the restricted stock units, except that in the event of such a termination in connection with a change in control, the restricted stock units will become fully vested. The employee will be entitled to receive one share of Zillow's Class A common stock for each then outstanding unit
Fair value of restricted shares issued	5,400,000
HotPads, Inc.
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Substituted incentive option awards granted in connection with acquisition		15,143
StreetEasy, Inc.
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Substituted incentive option awards granted in connection with acquisition		25,385
Non Employee Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option award of Class A common stock granted					23,010
Fair value of option award granted					$32.60
Expected volatility					54.00%
Risk-free interest rate					0.69%
Weighted-average expected life					3 years 6 months
Recognized compensation cost		800,000
Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option award of Class A common stock granted						500,000	500,000
Fair value of option award granted						$19	$12.23
Expected volatility						51.00%	49.00%
Risk-free interest rate						0.70%	0.60%
Weighted-average expected life						7 years 3 months 18 days	5 years
2011 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in number of shares of common stock available for issuance percentage		3.50%
Increase in number of shares of common stock available for issuance		3,500,000
Total number of shares available for issuance under awards		3,800,000
Exercise price per share fixed		100.00%
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding		86,835	230,127
Number of shares granted		3,255
Total unrecognized compensation cost		2,500,000
Unrecognized compensation cost expected recognition period		1 year 1 month 6 days
Total fair value of restricted stock vested		4,500,000	3,400,000	1,000,000
Restricted Stock | 2011 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares outstanding		139,002
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of vested units in the event of termination of employment		50.00%
Restricted stock unit, award vesting period	4 years							2 years
Number of shares outstanding		125,602	121,123
Number of shares granted	59,320	102,264						24,880
Total unrecognized compensation cost		10,800,000
Unrecognized compensation cost expected recognition period		2 years 6 months 26 days
Total fair value of restricted stock vested		7,400,000	10,800,000	0
Vesting commencement date of restricted shares									26-Mar-14
Terms of restricted stock unit award		In the event of termination of service of employment by Zillow without cause, 50% of the then unvested restricted stock units will become vested units, and the recipient will be entitled to receive one share of Zillow's Class A common stock for each then outstanding unit.
Fair value of restricted shares issued		3,200,000
Restricted Stock Units | Restricted Stock Unit Award Notice and Restricted Stock Unit Award Agreement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting commencement date of restricted shares		3-Jun-14
Restricted Stock Units | 2011 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted		298,916
Option Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of shares available for issuance under awards		1,110,524	1,513,264
Total unrecognized compensation cost		$90,700,000
Unrecognized compensation cost expected recognition period		3 years 1 month 6 days
Option award of Class A common stock granted		2,219,458
Option Awards | 2011 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period		7 years
Share based compensation arrangement by share based payment, award minimum exercisable period		3 months
Share based compensation arrangement by share based payment, award maximum exercisable period		12 months
Options vesting rights		Option awards granted under the 2011 Plan are typically granted with seven-year terms and typically vest 25% after 12 months and ratably thereafter over the next 36 months
Percentage of vested units in the event of termination of employment		25.00%
Option Awards | 2011 Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period		10 years
Restricted stock unit, award vesting period		36 months
Option Awards | 2011 Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock unit, award vesting period		12 months

Summary_of_Option_Award_Activi

Summary of Option Award Activity (Detail) (Option Awards, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Option Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Available for Grant, Beginning Balance	1,513,264
Shares Available for Grant, Authorized increase in plan shares	1,563,827
Shares Available for Grant, Granted	-2,219,458
Shares Available for Grant, Exercised	0
Shares Available for Grant, Forfeited or cancelled	252,891
Shares Available for Grant, Ending Balance	1,110,524	1,513,264
Number of Shares Subject to Existing Option Awards, Beginning Balance	5,156,706
Number of Shares Subject to Existing Option Awards, Authorized increase in plan shares	0
Number of Shares Subject to Existing Option Awards, Granted	2,219,458
Number of Shares Subject to Existing Option Awards, Exercised	-1,323,509
Number of Shares Subject to Existing Option Awards, Forfeited or cancelled	-252,891
Number of Shares Subject to Existing Option Awards, Ending Balance	5,799,764	5,156,706
Number of Shares Subject to Existing Option Awards, Vested and exercisable	1,685,583
Weighted-Average Exercise Price Per Share, Beginning Balance	$27.09
Weighted-Average Exercise Price Per Share, Authorized increase in plan shares	$0
Weighted-Average Exercise Price Per Share, Granted	$97.06
Weighted-Average Exercise Price Per Share, Exercised	$18.08
Weighted-Average Exercise Price Per Share, Forfeited or cancelled	$62.76
Weighted-Average Exercise Price Per Share, Ending Balance	$54.37	$27.09
Weighted-Average Exercise Price Per Share, Vested and exercisable	$21.95
Weighted-Average Remaining Contractual Life (Years)	5 years 3 months 26 days	5 years 5 months 5 days
Weighted-Average Remaining Contractual Life (Years), Vested and exercisable	3 years 9 months 7 days
Aggregate Intrinsic Value	$311,040,401	$283,008,505
Aggregate Intrinsic Value Vested, and exercisable	$141,486,370

Fair_Value_of_Option_Awards_Gr

Fair Value of Option Awards Granted, Excluding Non Employee Director Awards, Estimated at Date of Grant Using Black Scholes Merton Option Pricing Model (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected volatility, minimum	53.00%	50.00%	49.00%
Expected volatility, maximum	57.00%	54.00%	52.00%
Expected dividend yields
Risk-free interest rate, minimum	1.37%	0.70%	0.53%
Risk-free interest rate, maximum	1.55%	1.27%	0.76%
Weighted-average expected life	4 years 6 months 29 days	4 years 6 months 29 days	4 years 6 months 29 days
Weighted-average fair value of options granted	$44.34	$21.26	$13.79

Summary_of_Option_Awards_Outst

Summary of Option Awards Outstanding and Option Awards Vested and Exercisable (Detail) (Option Awards, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option Awards Outstanding, Number Outstanding	5,799,764	5,156,706
Option Awards Outstanding, Weighted- Average Remaining Contractual Life (Years)	5 years 3 months 26 days	5 years 5 months 5 days
Option Awards Outstanding, Weighted Average Exercise Price	$54.37	$27.09
Option Awards Vested and Exercisable, Number Exercisable	1,685,583
Option Awards Vested and Exercisable, Weighted Average Exercise Price	$21.95
$1.95 - $19.84
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option Awards Outstanding, Exercise Price, lower limit	$1.95
Option Awards Outstanding, Exercise Price, upper limit	$19.84
Option Awards Outstanding, Number Outstanding	888,955
Option Awards Outstanding, Weighted- Average Remaining Contractual Life (Years)	2 years 9 months 18 days
Option Awards Outstanding, Weighted Average Exercise Price	$3.87
Option Awards Vested and Exercisable, Number Exercisable	790,891
Option Awards Vested and Exercisable, Weighted Average Exercise Price	$3.78
$24.80 - $29.69
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option Awards Outstanding, Exercise Price, lower limit	$24.80
Option Awards Outstanding, Exercise Price, upper limit	$29.69
Option Awards Outstanding, Number Outstanding	582,168
Option Awards Outstanding, Weighted- Average Remaining Contractual Life (Years)	4 years 9 months 15 days
Option Awards Outstanding, Weighted Average Exercise Price	$28.19
Option Awards Vested and Exercisable, Number Exercisable	170,611
Option Awards Vested and Exercisable, Weighted Average Exercise Price	$28.07
$30.46 - $36.30
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option Awards Outstanding, Exercise Price, lower limit	$30.46
Option Awards Outstanding, Exercise Price, upper limit	$36.30
Option Awards Outstanding, Number Outstanding	545,314
Option Awards Outstanding, Weighted- Average Remaining Contractual Life (Years)	4 years 1 month 21 days
Option Awards Outstanding, Weighted Average Exercise Price	$31.08
Option Awards Vested and Exercisable, Number Exercisable	295,518
Option Awards Vested and Exercisable, Weighted Average Exercise Price	$31.03
$36.36 - $38.60
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option Awards Outstanding, Exercise Price, lower limit	$36.36
Option Awards Outstanding, Exercise Price, upper limit	$38.60
Option Awards Outstanding, Number Outstanding	1,268,964
Option Awards Outstanding, Weighted- Average Remaining Contractual Life (Years)	6 years 2 months 23 days
Option Awards Outstanding, Weighted Average Exercise Price	$36.43
Option Awards Vested and Exercisable, Number Exercisable	273,343
Option Awards Vested and Exercisable, Weighted Average Exercise Price	$36.50
$38.97 - $81.97
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option Awards Outstanding, Exercise Price, lower limit	$38.97
Option Awards Outstanding, Exercise Price, upper limit	$81.97
Option Awards Outstanding, Number Outstanding	343,766
Option Awards Outstanding, Weighted- Average Remaining Contractual Life (Years)	5 years 5 months 1 day
Option Awards Outstanding, Weighted Average Exercise Price	$60.99
Option Awards Vested and Exercisable, Number Exercisable	106,943
Option Awards Vested and Exercisable, Weighted Average Exercise Price	$54.31
$82.05
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option Awards Outstanding, Exercise Price, lower limit	$82.05
Option Awards Outstanding, Number Outstanding	1,019,380
Option Awards Outstanding, Weighted- Average Remaining Contractual Life (Years)	6 years 4 days
Option Awards Outstanding, Weighted Average Exercise Price	$82.05
$82.74 - $107.94
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option Awards Outstanding, Exercise Price, lower limit	$82.74
Option Awards Outstanding, Exercise Price, upper limit	$107.94
Option Awards Outstanding, Number Outstanding	593,028
Option Awards Outstanding, Weighted- Average Remaining Contractual Life (Years)	6 years 3 months 15 days
Option Awards Outstanding, Weighted Average Exercise Price	$95.20
Option Awards Vested and Exercisable, Number Exercisable	48,277
Option Awards Vested and Exercisable, Weighted Average Exercise Price	$88.38
$109.93 - $144.07
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option Awards Outstanding, Exercise Price, lower limit	$109.93
Option Awards Outstanding, Exercise Price, upper limit	$144.07
Option Awards Outstanding, Number Outstanding	530,891
Option Awards Outstanding, Weighted- Average Remaining Contractual Life (Years)	6 years 7 months 24 days
Option Awards Outstanding, Weighted Average Exercise Price	$126.56
$144.94
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option Awards Outstanding, Exercise Price, lower limit	$144.94
Option Awards Outstanding, Number Outstanding	21,478
Option Awards Outstanding, Weighted- Average Remaining Contractual Life (Years)	6 years 7 months 24 days
Option Awards Outstanding, Weighted Average Exercise Price	$144.94
$160.32
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Option Awards Outstanding, Exercise Price, lower limit	$160.32
Option Awards Outstanding, Number Outstanding	5,820
Option Awards Outstanding, Weighted- Average Remaining Contractual Life (Years)	6 years 6 months 26 days
Option Awards Outstanding, Weighted Average Exercise Price	$160.32

Summary_of_Restricted_Stock_Aw

Summary of Restricted Stock Award Activity (Detail) (Restricted Stock, USD $)	12 Months Ended
	Dec. 31, 2014
Restricted Stock
Shares of Restricted Stock
Unvested outstanding, beginning balance	230,127
Granted	3,255
Vested	-146,547
Forfeited or cancelled	0
Unvested outstanding, ending balance	86,835
Weighted-Average Grant-Date Fair Value
Unvested outstanding, beginning balance	$30.43
Granted	$80.91
Vested	$30.48
Forfeited or cancelled	$0
Unvested outstanding, ending balance	$32.25

Summary_of_Restricted_Stock_Un

Summary of Restricted Stock Units Activity (Detail) (Restricted Stock Units, USD $)	1 Months Ended		12 Months Ended
	Jun. 30, 2014	Apr. 30, 2014	Dec. 31, 2014
Restricted Stock Units
Restricted Stock Units
Unvested outstanding, beginning balance			121,123
Granted	24,880	59,320	102,264
Vested			-64,935
Forfeited or cancelled			-32,850
Unvested outstanding, ending balance			125,602
Weighted-Average Grant-Date Fair Value
Unvested outstanding, beginning balance			$64.07
Granted			$102.95
Vested			$76.28
Forfeited or cancelled			$72.40
Unvested outstanding, ending balance			$85.67

Effects_of_Share_Based_Compens

Effects of Share Based Compensation in Statements of Operations (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation	$34,085	$23,436	$6,611
Cost of Revenue
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation	1,844	737	380
Sales and Marketing
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation	7,320	10,969	2,433
Technology and Development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation	11,681	4,660	1,886
General and Administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation	$13,240	$7,070	$1,912

Dilutive_Securities_Included_i

Dilutive Securities Included in Computation of Earnings Per Share (Detail) (Class A Common Stock)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2012
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Class A common stock equivalents included in the computation of diluted net income per share	2,515
Option Awards
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Class A common stock equivalents included in the computation of diluted net income per share	2,469
Restricted Stock and Restricted Stock Units
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Class A common stock equivalents included in the computation of diluted net income per share	46

Antidilutive_Securities_Exclud

Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) (Class A Common Stock)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Class A common stock equivalents excluded from calculations of diluted net loss per share	3,021	3,350
Option Awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Class A common stock equivalents excluded from calculations of diluted net loss per share	2,903	3,179
Restricted Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Class A common stock equivalents excluded from calculations of diluted net loss per share	118	171

Commitments_and_Contingencies_1

Commitments and Contingencies - Additional Information (Detail) (USD $)	12 Months Ended			1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Nov. 30, 2010	Mar. 31, 2010	Sep. 30, 2010	Oct. 31, 2014	Feb. 28, 2014	Nov. 30, 2012	Apr. 30, 2012	Mar. 01, 2011
				Patent	Patent	Patent		sqft	sqft	sqft	sqft
Property Subject to or Available for Operating Lease [Line Items]
Rent expense	$7,500,000	$4,100,000	$2,600,000
Non-cancelable purchase commitments for content	45,777,000						50,000,000
Expiration date of lease	60 days
Smarter Agent
Property Subject to or Available for Operating Lease [Line Items]
Number of patents infringed					3
Number of patents-in-suit				3
Smarter Agent | Diverse Solutions
Property Subject to or Available for Operating Lease [Line Items]
Acquisition date	31-Oct-11
Smarter Agent | StreetEasy, Inc.
Property Subject to or Available for Operating Lease [Line Items]
Acquisition date	26-Aug-13
Smarter Agent | HotPads, Inc.
Property Subject to or Available for Operating Lease [Line Items]
Acquisition date	14-Dec-12
Lending Tree
Property Subject to or Available for Operating Lease [Line Items]
Number of patents infringed						2
Allegations and asserted defenses	In March 2014, a federal jury found that Zillow does not infringe the patents and that the patents asserted by LendingTree are invalid.
Operating Lease
Property Subject to or Available for Operating Lease [Line Items]
Rentable area of the premises								39,900	18,353	60,000	178,000
Seattle
Property Subject to or Available for Operating Lease [Line Items]
Outstanding letters of credit	1,800,000
New York
Property Subject to or Available for Operating Lease [Line Items]
Outstanding letters of credit	$1,100,000

Future_Minimum_Payments_for_Al

Future Minimum Payments for All Operating Leases (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Commitments and Contingencies Disclosure [Abstract]
2015	$9,809
2016	11,464
2017	15,231
2018	16,610
2019	15,114
All future years	80,270
Total future minimum lease payments	$148,498

Purchase_Commitments_for_Conte

Purchase Commitments for Content Related to Mobile Applications and Websites (Detail) (USD $)	Dec. 31, 2014	Oct. 31, 2014
In Thousands, unless otherwise specified
Commitments and Contingencies Disclosure [Abstract]
2015	$13,256
2016	6,070
2017	4,701
2018	5,250
2019	6,000
All future years	10,500
Total future purchase commitments	$45,777	$50,000

Segment_Information_and_Revenu2

Segment Information and Revenue - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2014
	Segment
Segment Reporting [Abstract]
Number of reportable segment	1

Revenue_Categories_Detail

Revenue Categories (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues:
Total Marketplace revenue	$267,242	$154,713	$86,670
Display revenue	58,651	42,832	30,180
Total revenue	325,893	197,545	116,850
Real Estate Revenue
Revenues:
Total Marketplace revenue	239,039	132,901	75,900
Mortgages Revenue
Revenues:
Total Marketplace revenue	$28,203	$21,812	$10,770

Subsequent_Events_Additional_I

Subsequent Events - Additional Information (Detail)	12 Months Ended	0 Months Ended
	Dec. 31, 2014	Jan. 07, 2015
Threewide Corporation
Subsequent Event [Line Items]
Platform services agreement date	7-Apr-11
Platform services agreement expiration date	7-Apr-15
Executive Officer
Subsequent Event [Line Items]
Options granted to date under various plan	One-sixteenth of the total number of shares subject to the option awards will vest and become exercisable on the two-year anniversary of the vesting commencement date. An additional 1/192nd of the total number of shares subject to the option awards will vest and become exercisable monthly thereafter over the next three years so that this portion of the award will be vested and exercisable five years from the vesting commencement date. One-sixteenth of the total number of shares subject to the option awards will vest and become exercisable on the three-year anniversary of the vesting commencement date. An additional 1/192nd of the total number of shares subject to the option awards will vest and become exercisable monthly thereafter over the next three years so that this portion of the award will be vested and exercisable six years from the vesting commencement date. One-sixteenth of the total number of shares subject to the option awards will vest and become exercisable on the four-year anniversary of the vesting commencement date. An additional 1/192nd of the total number of shares subject to the option awards will vest and become exercisable monthly thereafter over the next three years so that this portion of the award will be vested and exercisable seven years from the vesting commencement date.
Subsequent Events | Executive Officer
Subsequent Event [Line Items]
Stock option of Class A common stock granted		650,000
Sharebased payment award term		10 years