Zillow (ZG) 10-K 18 Feb 14 2013 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2013	Jun. 30, 2013	Feb. 11, 2014	Feb. 11, 2014
			Class A Common Stock	Class B Common Stock
Document Information [Line Items]	'	'	'	'
Document Type	'10-K	'	'	'
Amendment Flag	'false	'	'	'
Document Period End Date	31-Dec-13	'	'	'
Document Fiscal Year Focus	'2013	'	'	'
Document Fiscal Period Focus	'FY	'	'	'
Trading Symbol	'Z	'	'	'
Entity Registrant Name	'ZILLOW INC	'	'	'
Entity Central Index Key	'0001334814	'	'	'
Current Fiscal Year End Date	'--12-31	'	'	'
Entity Well-known Seasoned Issuer	'Yes	'	'	'
Entity Current Reporting Status	'Yes	'	'	'
Entity Voluntary Filers	'No	'	'	'
Entity Filer Category	'Large Accelerated Filer	'	'	'
Entity Common Stock, Shares Outstanding	'	'	33,011,384	6,468,892
Entity Public Float	'	$1,270,616,234	'	'

Balance_Sheets

Balance Sheets (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$201,760	$150,040
Short-term investments	93,531	44,054
Accounts receivable, net of allowance for doubtful accounts of $1,850 and $965 at December 31, 2013 and 2012, respectively	15,234	8,655
Prepaid expenses and other current assets	4,987	2,652
Total current assets	315,512	205,401
Long-term investments	142,435	9,389
Property and equipment, net	27,408	16,948
Goodwill	93,213	54,284
Intangible assets, net	29,149	21,248
Other assets	346	279
Total assets	608,063	307,549
Current liabilities:	'	'
Accounts payable	4,724	3,158
Accrued expenses and other current liabilities	11,377	6,318
Accrued compensation and benefits	4,440	2,514
Deferred revenue	12,298	8,349
Deferred rent, current portion	546	401
Total current liabilities	33,385	20,740
Deferred rent, net of current portion	6,882	6,492
Commitments and contingencies (Note 13)	'	'
Shareholders' equity:	'	'
Additional paid-in capital	651,913	351,981
Accumulated deficit	-84,121	-71,668
Total shareholders' equity	567,796	280,317
Total liabilities and shareholders' equity	608,063	307,549
Convertible Preferred Stock	'	'
Shareholders' equity:	'	'
Preferred stock	'	'
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

Balance_Sheets_Parenthetical

Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, except Share data, unless otherwise specified
Accounts receivable, allowance for doubtful accounts	$1,850	$965
Convertible Preferred Stock	'	'
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	30,000,000	30,000,000
Preferred stock, shares issued	'	'
Preferred stock, shares outstanding	'	'
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	32,934,074	26,414,414
Common stock, shares outstanding	32,934,074	26,414,414
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	6,468,892	7,462,526
Common stock, shares outstanding	6,468,892	7,462,526

Statements_of_Operations

Statements of Operations (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Income Statement [Abstract]	'		'		'
Revenue	$197,545		$116,850		$66,053
Costs and expenses:	'		'		'
Cost of revenue (exclusive of amortization)	18,810	[1]	14,043	[1]	10,575	[1]
Sales and marketing	108,891		49,105		25,725
Technology and development	48,498		26,614		14,143
General and administrative	38,295	[2]	21,291	[2]	14,613	[2]
Total costs and expenses	214,494		111,053		65,056
Income (loss) from operations	-16,949		5,797		997
Other income	385		142		105
Income (loss) before income taxes	-16,564		5,939		1,102
Income tax benefit	4,111		'		'
Net income (loss)	-12,453		5,939		1,102
Net income (loss) attributable to common shareholders	($12,453)		$5,939		'
Net income (loss) per share attributable to common shareholders-basic	($0.35)		$0.20		'
Net income (loss) per share attributable to common shareholders-diluted	($0.35)		$0.18		'
Weighted-average shares outstanding-basic	36,029		30,194		19,815
Weighted-average shares outstanding-diluted	36,029		32,709		22,305
[1]	Amortization of website development costs and intangible assets included in technology and development $ 19,791 $ 11,179 $ 5,384
[2]	General and administrative includes a facility exit charge as follows: $ - $ - $ 1,737

Statements_of_Operations_Paren

Statements of Operations (Parenthetical) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statement [Abstract]	'	'	'
Amortization of website development costs and intangible assets included in technology and development	$19,791	$11,179	$5,384
General and administrative includes a facility exit charge as follows	'	'	$1,737

Statements_of_Shareholders_Equ

Statements of Shareholders' Equity (USD $)	Total	Convertible Preferred Stock - Series A	Convertible Preferred Stock - Series B	Convertible Preferred Stock - Series C	Class A Common Stock	Class B Common Stock	Class C Common Stock	Additional Paid-in Capital	Accumulated Deficit
In Thousands, except Share data	USD ($)	USD ($)	USD ($)	USD ($)	USD ($)	USD ($)		USD ($)	USD ($)
Beginning Balance at Dec. 31, 2010	$17,448	$2	$1	$1	'	$1	'	$96,152	($78,709)
Beginning Balance (in shares) at Dec. 31, 2010	'	17,931,034	6,933,103	6,489,660	1,290,602	9,528,313	2,305,980	'	'
Issuance of Class A common stock upon exercise of stock options	2,917	'	'	'	'	'	'	2,917	'
Issuance of Class A common stock upon exercise of stock options (in shares)	'	'	'	'	1,169,121	'	'	'	'
Share-based compensation expense	2,545	'	'	'	'	'	'	2,545	'
Class A common stock issued in connection with an acquisition	910	'	'	'	'	'	'	910	'
Class A common stock issued in connection with an acquisition (in shares)	'	'	'	'	207,100	'	'	'	'
Conversion of convertible preferred stock to Class A common stock in connection with initial public offering	'	-2	-1	-1	1	'	'	3	'
Conversion of convertible preferred stock to Class A common stock in connection with initial public offering (in shares)	'	-17,931,034	-6,933,103	-6,489,660	9,276,190	'	'	'	'
Conversion of Class C common stock to Class A common stock in connection with initial public offering (in shares)	'	'	'	'	2,305,980	'	-2,305,980	'	'
Issuance of Class A common stock in connection with public offering, net of issuance costs of $12900 for the year ended December 31, 2013 and $8601 for the year ended December 31, 2012 and $8,835 for the year ended December 31, 2011	70,791	'	'	'	1	'	'	70,790	'
Issuance of Class A common stock in connection with public offering (in shares)	'	'	'	'	3,981,300	'	'	'	'
Issuance of Class A common stock in concurrent private placement in connection with initial public offering	5,500	'	'	'	'	'	'	5,500	'
Issuance of Class A common stock in concurrent private placement in connection with initial public offering (in shares)	'	'	'	'	274,999	'	'	'	'
Issuance of restricted shares of Class A common stock	'	'	'	'	75,000	'	'	'	'
Net income and total comprehensive income	1,102	'	'	'	'	'	'	'	1,102
Ending Balance at Dec. 31, 2011	101,213	'	'	'	2	1	'	178,817	-77,607
Ending 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	'	'	'	'
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 $12900 for the year ended December 31, 2013 and $8601 for the year ended December 31, 2012 and $8,835 for the year ended December 31, 2011	156,727	'	'	'	1	'	'	156,726	'
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 and total comprehensive income	5,939	'	'	'	'	'	'	'	5,939
Ending Balance at Dec. 31, 2012	280,317	'	'	'	3	1	'	351,981	-71,668
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	-993,634	'	'	'
Conversion of convertible preferred stock to Class A common stock in connection with initial public offering (in shares)	'	'	'	'	9,276,190	'	'	'	'
Conversion of Class C common stock to Class A common stock in connection with initial public offering (in shares)	'	'	'	'	2,305,980	'	'	'	'
Issuance of Class A common stock in connection with public offering, net of issuance costs of $12900 for the year ended December 31, 2013 and $8601 for the year ended December 31, 2012 and $8,835 for the year ended December 31, 2011	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 and total comprehensive income	-12,453	'	'	'	'	'	'	'	-12,453
Ending Balance at Dec. 31, 2013	$567,796	'	'	'	$3	$1	'	$651,913	($84,121)
Ending Balance (in shares) at Dec. 31, 2013	'	'	'	'	32,934,074	6,468,892	'	'	'

Statements_of_Shareholders_Equ1

Statements of Shareholders' Equity (Parenthetical) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement Of Stockholders Equity [Abstract]	'	'	'
Stock issuance costs	$12,900	$8,601	$8,835

Statements_of_Cash_Flows

Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating activities	'	'	'
Net income (loss)	($12,453)	$5,939	$1,102
Adjustments to reconcile net income (loss) to net cash provided by operating activities:	'	'	'
Depreciation and amortization	23,254	12,773	7,190
Facility exit charge	'	'	1,737
Share-based compensation expense	23,436	6,611	1,945
Release of valuation allowance on certain deferred tax assets	-4,111	'	'
Loss on disposal of property and equipment	910	353	157
Bad debt expense	1,907	1,227	594
Deferred rent	400	5,469	1,243
Amortization of bond premium	624	751	181
Changes in operating assets and liabilities:	'	'	'
Accounts receivable	-7,571	-3,458	-2,208
Prepaid expenses and other assets	-1,543	650	-2,882
Accounts payable	1,497	991	916
Accrued expenses	1,038	1,776	2,460
Deferred revenue	3,910	2,530	2,391
Net cash provided by operating activities	31,298	35,612	14,826
Investing activities	'	'	'
Proceeds from investment maturities	53,000	28,434	4,750
Purchases of investments	-236,147	-38,397	-47,772
Purchases of property and equipment	-22,047	-15,991	-7,686
Purchases of intangible assets	-3,925	-4,073	-1,135
Acquisitions, net of cash acquired of $0 in 2013, $2,879 in 2012 and $0 in 2011	-42,708	-67,645	-6,540
Net cash used in investing activities	-251,827	-97,672	-58,383
Financing activities	'	'	'
Proceeds from exercise of Class A common stock options	18,350	7,448	2,917
Proceeds from public offering, net of offering costs	253,899	156,726	70,788
Proceeds from concurrent private placement	'	'	5,500
Net cash provided by financing activities	272,249	164,174	79,205
Net increase in cash and cash equivalents during period	51,720	102,114	35,648
Cash and cash equivalents at beginning of period	150,040	47,926	12,278
Cash and cash equivalents at end of period	201,760	150,040	47,926
Noncash transactions:	'	'	'
Capitalized share-based compensation	3,817	2,379	600
Class A common stock issued in connection with an acquisition	'	'	910
Write-off of fully depreciated property and equipment	$3,697	$2,986	$2,133

Statements_of_Cash_Flows_Paren

Statements of Cash Flows (Parenthetical) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement Of Cash Flows [Abstract]	'	'	'
Convertible Preferred Stock	$0	$2,879	$0

Organization_and_Description_o

Organization and Description of Business	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Organization and Description of Business	'
	Note 1. Organization and Description of Business
	Zillow, Inc. (the “Company,” “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 Mortgage Marketplace, 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, Agentfolio, Mortech, HotPads and StreetEasy. Zillow provides products and services to help consumers through every stage of homeownership – buying, selling, renting, borrowing and remodeling.
	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: 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; acquisitions and investments; 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, 2013
Accounting Policies [Abstract]	'
Summary of Significant Accounting Policies	'
	Note 2. Summary of Significant Accounting Policies
	Basis of Presentation
	These 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. Estimates are used for 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. 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.
	Prior Period Adjustments
	The balance sheet as of December 31, 2012 has been revised to correct an immaterial error in the presentation of property and equipment, net and current and noncurrent deferred rent, which were understated by equal amounts of $3.3 million, related to leasehold improvements made that were funded by landlord allowances. The statement of cash flows for the year ended December 31, 2012 has been revised to correct the immaterial error in net cash provided by operating activities and net cash used in investing activities, which were understated by equal amounts of $3.3 million.
	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, commercial paper, and corporate notes and bonds. 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.
	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 five to 7.5 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 but unrecognized subscription revenue, 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, primarily on an individual subscription basis, and mortgage professionals and brand advertisers. Our two revenue categories are marketplace revenue and display revenue.
	Marketplace Revenue. Marketplace revenue consists of real estate revenue and mortgages revenue. Real estate revenue primarily includes subscriptions sold to real estate agents under our Premier Agent program, as well as revenue generated by Zillow Rentals. Mortgages revenue primarily includes Zillow Mortgage Marketplace advertising sold to mortgage lenders on a cost-per-click, or CPC, basis. Mortgages revenue also includes revenue generated by Mortech, a company we acquired in November 2012 that 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 original flagship subscription 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 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 customers for our Platinum Premier Agent subscription product based on the number of impressions delivered on our buyer’s agent list in zip codes purchased. Our Platinum Premier Agent subscription 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 subscription 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, which is typically over a period of six 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 Mortgage Marketplace, 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 Mortgage Marketplace 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 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, 2013, 2012 or 2011.
	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 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, 2013, 2012 and 2011, expenses attributable to research and development for our business totaled $41.7 million, $22.0 million and $10.7 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 stock options. In valuing our options, 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 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 options as the average of the vesting option 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 share options. 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 stock options 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 and restricted stock 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, 2013, 2012 and 2011, expenses attributable to advertising totaled $38.7 million, $11.1 million and $4.0 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 July 2013, the Financial Accounting Standards Board (“FASB”) issued guidance on the presentation of certain unrecognized tax benefits in the financial statements. This guidance provides that a liability related to an unrecognized tax benefit must be offset against a deferred tax asset for a net operating loss carryforward, a similar tax loss or a tax credit carryforward if such settlement is required or expected in the event the uncertain tax position is disallowed. This guidance is effective for interim and annual reporting periods beginning after December 15, 2013, with earlier adoption permitted, and may be applied prospectively or retrospectively. We expect to adopt this guidance on January 1, 2014. The adoption of this guidance is not expected to have a significant impact on our financial position, results of operations or cash flows, as we have provided a full valuation allowance against our net deferred tax assets.
In February 2013, the FASB issued guidance on the reporting of amounts reclassified out of accumulated other comprehensive income. An entity must report the effect of significant reclassifications out of accumulated other comprehensive income on the respective line items in net income if the amount being reclassified is required under GAAP to be reclassified in its entirety to net income. For other amounts that are not required under GAAP to be reclassified in their entirety to net income in the same reporting period, an entity is required to cross-reference other disclosures required under GAAP that provide additional detail about those amounts. This guidance is effective for interim and annual reporting periods beginning after December 15, 2012, with earlier adoption permitted, and must be applied prospectively. We adopted this guidance on January 1, 2013. The adoption of this guidance did not have any impact on our financial position, results of operations or cash flows, as we do not have any items of other comprehensive income in any period presented.
In June 2011, the FASB issued guidance on the presentation of comprehensive income to increase the prominence of other comprehensive income in the financial statements. An entity has the option to present the components of net income and comprehensive income in either one or two consecutive financial statements. This guidance is effective for interim and annual reporting periods beginning after December 15, 2011, with earlier adoption permitted, and must be applied retrospectively. We adopted this guidance on January 1, 2012. The adoption of this guidance did not have any impact on our financial position, results of operations or cash flows as we do not have any items of other comprehensive income in any period presented, and therefore, we are not required to report other comprehensive income or comprehensive income.

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2013
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, therefore, these assets are recorded at fair value on a recurring basis and classified as Level 1 in the fair value hierarchy.
	Short-term and long-term investments—Our investments consist of fixed income securities, which include U.S. government agency securities, commercial paper, and corporate notes and bonds. 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. Our U.S. government agency securities are classified as Level 1 in the fair value hierarchy. Our commercial paper and corporate notes and bonds are classified as Level 2 in the fair value hierarchy.
	Of the short-term investments and long-term investments on hand as of December 31, 2013, 39.6% mature in 2014 and the remaining 60.4% mature in 2015.
	The following tables present the balances of assets measured at fair value on a recurring basis as of the dates presented (in thousands):
			December 31, 2013
			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
			December 31, 2012
			Total		Level 1		Level 2
	Cash equivalents:
	Money market funds		$	143,246	$	143,246	$	—
	Short-term investments:
	U.S government agency securities			26,085		26,085		—
	Commercial paper			16,965		—		16,965
	Corporate notes and bonds			1,004		—		1,004
	Long-term investments:
	U.S government agency securities			7,079		7,079		—
	Corporate notes and bonds			2,310		—		2,310
	Total		$	196,689	$	176,410	$	20,279
	We did not have any Level 3 assets measured at fair value on a recurring basis as of December 31, 2013 or 2012. There were no liabilities measured at fair value on a recurring basis as of December 31, 2013 or 2012.

Accounts_Receivable_Net

Accounts Receivable, Net	12 Months Ended
	Dec. 31, 2013
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,
		2013			2012
	Accounts receivable	$	13,793		$	9,503
	Unbilled accounts receivable		3,291			117
	Less: allowance for doubtful accounts		(1,850	)		(965	)
	Accounts receivable, net	$	15,234		$	8,655
	The following table presents the changes in the allowance for doubtful accounts for the periods presented (in thousands):
		Year Ended December 31,
		2013			2012			2011
	Allowance for doubtful accounts:
	Balance, beginning of period	$	965		$	683		$	501
	Additions charged to expense		1,907			1,227			594
	Less: write-offs, net of recoveries and other adjustments		(1,022	)		(945	)		(412	)
	Balance, end of period	$	1,850		$	965		$	683

Property_and_Equipment_Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2013
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,
		2013			2012
	Website development costs	$	50,408		$	33,448
	Computer equipment		8,238			8,380
	Leasehold improvements		7,320			4,145
	Software		1,807			1,209
	Construction-in-progress		3,289			3,093
	Office equipment, furniture and fixtures		3,661			2,186
	Property and equipment		74,723			52,461
	Less: accumulated amortization and depreciation		(47,315	)		(35,513	)
	Property and equipment, net	$	27,408		$	16,948
	We recorded amortization and depreciation expense related to property and equipment other than website development costs of $3.5 million, $1.6 million and $1.8 million, respectively, during the years ended December 31, 2013, 2012 and 2011.
	We capitalized $17.3 million, $11.5 million and $5.5 million, respectively, in website development costs during the years ended December 31, 2013, 2012 and 2011. Amortization expense for website development costs included in technology and development expenses was $12.2 million, $6.9 million and $4.1 million, respectively, for the years ended December 31, 2013, 2012 and 2011.
	Construction-in-progress primarily consists of website development costs that are capitalizable, but for which the associated applications had not been placed in service.

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2013
Business Combinations [Abstract]	'
Acquisitions	'
	Note 6. Acquisitions
	StreetEasy, Inc.
	On August 26, 2013, through our wholly owned subsidiary, Strawberry Acquisition, Inc., a Delaware corporation (“Merger Sub”), we consummated our acquisition of StreetEasy, Inc., formerly known as NMD Interactive, Inc., d/b/a StreetEasy, a Delaware corporation (“StreetEasy”), pursuant to an Agreement and Plan of Merger (the “Merger Agreement”) by and among Zillow, StreetEasy, Merger Sub and Shareholder Representative Services LLC, acting as the stockholder representative, dated August 16, 2013. Under the terms and subject to the conditions of the Merger Agreement, Merger Sub merged with and into StreetEasy with StreetEasy remaining as the surviving company and a wholly owned subsidiary of Zillow (the “Merger”). On December 30, 2013, StreetEasy was merged with and into the Company, with the Company remaining as the surviving entity. The acquisition aligns with our growth strategies, including focusing on consumers and deepening, strengthening, and expanding our marketplaces. With the addition of StreetEasy, we expanded our audience and brand awareness by leveraging StreetEasy’s leadership among both consumers and professionals in the New York region and, in particular, the New York for-sale and rentals market.
	The total Merger consideration payable to StreetEasy equity holders was approximately $50 million in cash, less certain transaction expenses and as adjusted at closing based on StreetEasy’s net working capital, cash and debt. All vested options to purchase shares of StreetEasy’s common stock were cancelled and, in settlement of such cancellation, the holders of such options became entitled to receive cash payments representing a portion of the Merger consideration as described in the Merger Agreement. A portion of the Merger consideration has been attributed to the substitution of unvested stock options of StreetEasy outstanding as of the closing for stock options to purchase shares of our Class A common stock at an exchange ratio implied by the Merger consideration as described in the Merger Agreement. In connection with the closing, $5 million of the Merger consideration otherwise payable to StreetEasy stockholders and holders of vested stock options has been deposited in a third-party escrow account to secure certain indemnification obligations of those equity holders. As of December 31, 2013, accrued expenses and other current liabilities includes $5.5 million payable to certain equity holders of StreetEasy who have not yet claimed their Merger consideration in connection with the acquisition, and prepaid expenses and other current assets includes $0.5 million related to an adjustment to StreetEasy’s net working capital.
	Our acquisition of StreetEasy has been accounted for as a business combination, and assets acquired and liabilities assumed were recorded at their estimated fair values as of August 26, 2013. Goodwill, which represents the expected synergies from combining the acquired assets and the operations of the acquirer, as well as intangible assets that do not qualify for separate recognition, is measured as of the acquisition date as the excess of consideration transferred, which is also measured at fair value, and the net of the fair values of the assets acquired and the liabilities assumed as of the acquisition date. The purchase price was approximately $48.2 million, as summarized in the following table (in thousands):
	Cash payable for the outstanding stock of StreetEasy	$	42,821
	Cash payable for the cancellation of vested options to purchase shares of StreetEasy’s common stock		2,989
	Certain transaction expenses and other costs incurred by StreetEasy		1,924
	Substituted unvested stock options attributable to pre-combination service		430
	Total purchase price	$	48,164
	The fair value of StreetEasy’s unvested stock options substituted in connection with the acquisition that relate to post-combination services will be recorded as share-based compensation expense over the related vesting periods.
	Identifiable intangible assets acquired consisted of the following (in thousands):
					Estimated
					Amortization
					Period
					(in years)
	Developed technology	$	4,500			5
	Customer relationships		4,900			5
	Trademarks		2,200			5
	Total intangible assets acquired	$	11,600
	The preliminary estimated fair value of the intangible assets acquired was determined by the Company, and we considered or relied in part upon a valuation report of a third-party expert. We used a cost approach to measure the fair value of the developed technology based on the estimated cost to recreate the technology. We used an income approach to measure the fair value of the customer relationships based on the excess earnings method, whereby the fair value is estimated based upon the present value of cash flows that the applicable asset is expected to generate. We used an income approach to measure the fair value of the trademarks based on the relief-from-royalty method. These fair value measurements were based on Level 3 measurements under the fair value hierarchy. Net tangible assets were valued at their respective carrying amounts, as we believe that these amounts approximate their current fair values.
	The total purchase consideration has been allocated to the assets acquired and liabilities assumed, including identifiable intangible assets, based on their respective fair values at the acquisition date. Based upon the fair values determined by us, in which we considered or relied in part upon a valuation report of a third-party expert, the total purchase price was allocated as follows (in thousands):
	Accounts receivable	$	917
	Prepaid expenses and other current assets		191
	Property and equipment		1,138
	Other identifiable tangible assets		144
	Total tangible assets		2,390
	Accounts payable		(72	)
	Accrued expenses and other current liabilities		(175	)
	Accrued compensation and benefits		(223	)
	Other identifiable liabilities		(174	)
	Net deferred tax liability		(4,111	)
	Total liabilities		(4,755	)
	Net acquired liabilities		(2,365	)
	Identifiable intangible assets		11,600
	Goodwill		38,929
	Total purchase price allocation	$	48,164
	Our estimates and assumptions related to the purchase price allocation are preliminary and subject to change during the measurement period (up to one year from the acquisition date) as we finalize the amount of goodwill recorded in connection with the acquisition, which may be impacted by an adjustment in StreetEasy’s acquisition date working capital.
	Acquisition-related expenses incurred of $0.4 million for the year ended December 31, 2013, including legal and accounting fees and other external costs directly related to the acquisition, were expensed as incurred, and are included in general and administrative expenses.
	The results of operations related to the acquisition of StreetEasy have been included in our financial statements since the date of acquisition of August 26, 2013, and are not significant.
	Unaudited Pro Forma Financial Information
	The following unaudited pro forma condensed combined financial information gives effect to the acquisition of StreetEasy as if it were consummated on January 1, 2012 (the beginning of the comparable prior reporting period), and includes pro forma adjustments related to the amortization of acquired intangible assets, share-based compensation expense and direct and incremental transaction costs reflected in the historical financial statements. The unaudited pro forma condensed combined financial information is presented for informational purposes only. The unaudited pro forma condensed combined financial information is not intended to represent or be indicative of the results of operations that would have been reported had the acquisition occurred on January 1, 2012 and should not be taken as representative of future results of operations of the combined company.
	The following table presents the unaudited pro forma condensed combined financial information (in thousands, except per share amounts):
		Year Ended
		December  31,
		2013			2012
	Revenue	$	202,086		$	122,547
	Net income (loss)	$	(14,121	)	$	4,940
	Net income (loss) per share—basic	$	(0.39	)	$	0.16
	Net income (loss) per share—diluted	$	(0.39	)	$	0.15

Goodwill

Goodwill	12 Months Ended
	Dec. 31, 2013
Goodwill And Intangible Assets Disclosure [Abstract]	'
Goodwill	'
	Note 7. Goodwill
	The following table presents the change in goodwill from December 31, 2012 through December 31, 2013 (in thousands):
	Balance as of December 31, 2012	$	54,284
	Goodwill recorded in connection with the acquisition of StreetEasy		38,929
	Balance as of December 31, 2013	$	93,213
	The goodwill recorded in connection with the acquisition of StreetEasy is not deductible for tax purposes.

Intangible_Assets

Intangible Assets	12 Months Ended
	Dec. 31, 2013
Goodwill And Intangible Assets Disclosure [Abstract]	'
Intangible Assets	'
	Note 8. Intangible Assets
	The following tables present the detail of intangible assets subject to amortization as of the dates presented (in thousands):
		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
		December 31, 2012
		Cost		Accumulated			Net
				Amortization
	Purchased content	$	9,044	$	(6,015	)	$	3,029
	Developed technology		14,335		(1,534	)		12,801
	Customer relationships		4,875		(387	)		4,488
	Trademarks		1,061		(131	)		930
	Total	$	29,315	$	(8,067	)	$	21,248
	Amortization expense recorded for intangible assets for the years ended December 31, 2013, 2012 and 2011 was $7.6 million, $4.3 million and $1.3 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, 2013 and 2012 was approximately 4.5 years and 4.9 years, respectively.
	Estimated future amortization expense for intangible assets, including amortization related to future commitments, as of December 31, 2013 is as follows (in thousands):
	2014	$	10,341
	2015		10,074
	2016		9,074
	2017		7,343
	2018		4,935
	All future years		1,261
	Total	$	43,028

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	Note 9. Income Taxes
	We are subject to federal and state income taxes in the United States. For the years ended December 31, 2013, 2012 and 2011, we did not have reportable taxable income and, therefore, no related tax liability or expense has been recorded in the 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 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,
		2013			2012			2011
	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,
		2013			2012			2011
	Tax expense at federal statutory rate		(34.0	%)		34	%		34	%
	State income taxes, net of federal tax benefit		(5.8	%)		0	%		0	%
	Nondeductible expenses		3.1	%		9.2	%		10	%
	Share-based compensation		0.2	%		3.5	%		37.1	%
	Research and development credits		(23.3	%)		0	%		(32.6	%)
	Valuation allowance		35	%		(46.7	%)		(48.5	%)
	Effective tax rate		(24.8	%)		0	%		0	%
	Deferred federal 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,
		2013			2012
	Deferred tax assets:
	Federal and state net operating loss carryforwards	$	24,152		$	19,899
	Share-based compensation		4,467			2,712
	Goodwill		1,776			591
	Start-up and organizational costs		491			554
	Research and development credits		5,123			1,255
	Accruals and reserves		901			792
	Other		3,415			1,606
	Total deferred tax assets		40,325			27,409
	Deferred tax liabilities:
	Website and software development costs		(4,927	)		(2,934	)
	Intangibles		(6,519	)		(3,037	)
	Depreciation and amortization		(1,579	)		(67	)
	Net deferred tax assets before valuation allowance		27,300			21,371
	Less: valuation allowance		(27,300	)		(21,371	)
	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, 2013 and 2012 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 $5.9 million during the year ended December 31, 2013 and decreased by $3.6 million during the year ended December 31, 2012.
	We have accumulated federal tax losses of approximately $236.5 million and $115.7 million as of December 31, 2013 and 2012, respectively, which are available to reduce future taxable income. We have accumulated state tax losses of approximately $6.1 million (tax effected) as of December 31, 2013. As of December 31, 2013, approximately $167.9 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 $5.1 million and $1.3 million, respectively, as of December 31, 2013 and 2012, 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.
	We are currently not under audit in any tax jurisdiction. Tax years from 2010 through 2013 are currently open for audit by federal and state taxing authorities.
	Changes for unrecognized tax benefits for the periods presented are as follows (in thousands):
	Balance at January 1, 2011	$	866
	Gross increases—current-period tax positions		359
	Balance at December 31, 2011	$	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
	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, 2013
Equity [Abstract]	'
Shareholders' Equity	'
	Note 10. 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, 2013 or 2012.
	Upon the effectiveness of our registration statement on Form S-1 (File No. 333-173570) on July 19, 2011, all of the outstanding shares of convertible preferred stock and all of the outstanding shares of Class C common stock automatically converted into 9,276,190 and 2,305,980 shares of Class A common stock, respectively. 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, 2013, 993,634 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,
		2013		2012
	Class A common stock options outstanding		5,156,706		5,462,672
	Class A common stock available for grant under equity plan		1,513,264		306,535
	Restricted stock units outstanding		121,123		296,004
	Shares issuable upon conversion of outstanding Class B common stock		6,468,892		7,462,526
	Total		13,259,985		13,527,737

ShareBased_Awards

Share-Based Awards	12 Months Ended
	Dec. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
Share-Based Awards	'
	Note 11. 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 replaced our 2005 Equity Incentive Plan. The 2011 Plan was subsequently amended and restated effective as of June 1, 2012, to, among other things, increase the total number of authorized shares and include the material terms of performance goals for performance-based awards. The 2011 Plan was further amended effective as of May 31, 2013 to increase the number of authorized shares of Class A common stock available for awards under the 2011 Plan by 1,500,000 shares. 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 or restricted stock 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.
	Stock Options
	All stock options granted from inception through December 31, 2013 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. Options 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 stock options 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 is ten years from the date of grant. Any portion of an option 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 options after 3 months following their termination of employment or 12 months in the event of termination by reason of death, disability or retirement. Options 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 options 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 options granted to the Company’s chief executive officer in December 2012 and January 2013 (the “Executive Awards”).
	The following table summarizes stock option activity for the year ended December 31, 2013:
		Shares			Number of			Weighted-			Weighted-		Aggregate
		Available			Shares			Average			Average		Intrinsic
		for Grant			Subject to			Exercise			Remaining		Value
					Existing			Price Per			Contractual
					Options			Share			Life (Years)
	Outstanding at January 1, 2013		321,678			5,462,672		$	14.48			4.88	$	78,912,364
	Authorized increase in plan shares		2,887,064			—			—
	Granted		(1,984,157	)		2,009,542			43.87
	Exercised		—			(2,026,829	)		9.03
	Forfeited or cancelled		288,679			(288,679	)		31.93
	Outstanding at December 31, 2013		1,513,264			5,156,706			27.09			5.43		283,008,505
	Vested and exercisable at December 31, 2013					1,575,015			12.02			3.93		109,787,836
	The shares available for grant identified in the above table exclude stock option awards for an aggregate of 25,385 shares, which stock option awards were granted in substitution of stock option awards previously granted by StreetEasy. Pursuant to the terms of the 2011 Plan, such substituted stock option awards do not reduce the number of shares available for future issuance under the 2011 Plan. As of December 31, 2013, the numbers above do not include 96,792 shares of restricted stock and 121,123 restricted stock units granted pursuant to our 2011 Plan.
	As of December 31, 2013, there was a total of $42.3 million in unrecognized compensation cost related to unvested stock options, which is expected to be recognized over a weighted-average period of 3.2 years. The total intrinsic value of options exercised during the years ended December 31, 2013, 2012 and 2011 was $114.4 million, $49.7 million and $11.3 million, respectively.
	The fair value of options granted, excluding Nonemployee Director Awards and the Executive Awards, 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,
		2013			2012			2011
	Expected volatility		50% – 54	%		49% – 52	%		49% – 52	%
	Expected dividend yields		—			—			—
	Average risk-free interest rate		0.70% – 1.27	%		0.53% – 0.76	%		0.79% – 1.87	%
	Weighted-average expected life		4.58 years			4.58 years			4.58 years
	Weighted-average fair value of options granted	$	21.26		$	13.79		$	4.66
	In March 2013, stock options for an aggregate of 30,690 shares of our Class A common stock were granted as Nonemployee Director Awards, which are fully vested and exercisable on the grant date. The fair value of options granted for the March 2013 Nonemployee Director Awards, $16.29 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 0.36%, and a weighted-average expected life of 3.5 years. During the year ended December 31, 2013, share-based compensation expense recognized in our statement of operations related to the March 2013 Nonemployee Director Awards was $0.5 million, and is included in general and administrative expenses.
	On January 24, 2013, an option for 500,000 shares of our Class A common stock was granted to the Company’s chief executive officer as an Executive Award. One-eighth of the total number of shares subject to the option will vest and become exercisable on the three-year anniversary of the grant date. An additional 1/96th of the total number of shares subject to the option 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 grant date. One-eighth of the total number of shares subject to the option will vest and become exercisable on the four-year anniversary of the grant date. An additional 1/96th of the total number of shares subject to the option 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 grant date. The option has a ten-year term. The fair value of the option, $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.
	The fair value of stock options vested for the years ended December 31, 2013, 2012 and 2011 was $1.2 million, $0.8 million and $1.0 million, respectively.
	The following table summarizes information about options outstanding and vested and exercisable stock options as of December 31, 2013:
		Options Outstanding									Options Vested and Exercisable
	Exercise Price or Range	Number			Weighted-			Weighted Average			Number		Weighted
		Outstanding			Average			Exercise Price			Exercisable		Average  Exercise
					Remaining								Price
					Contractual Life
					(Years)
	$0.08 – $3.85		839,063			3.24		$	3.43			706,969	$	3.47
	$3.89 – $5.98		683,918			4.15			3.89			341,559		3.89
	$6.32 – $29.50		830,733			5.58			25.38			173,466		20.26
	$29.69 – $30.46		527,311			5.07			30.4			177,099		30.38
	$30.60 – $36.30		284,158			5.15			32.12			112,581		31.41
	$36.36		1,393,635			7.14			36.36			2,013		36.36
	$36.72 – $89.09		518,204			6.24			57.18			61,328		42.52
	$90.05 – $96.24		65,328			6.59			94.84			—		—
	$96.25		13,756			6.69			96.25			—		—
	$99.09		600			6.67			99.09			—		—
	Total		5,156,706			5.43			27.09			1,575,015		12.02
	Restricted Stock Awards
	The following table summarizes restricted stock award activity for the year ended December 31, 2013:
		Shares of			Weighted-
		Restricted Stock			Average Grant-
					Date Fair
					Value
	Unvested outstanding at January 1, 2013		340,103		$	30.37
	Granted		3,673			44.66
	Vested		(108,379	)		30.94
	Forfeited or cancelled		(5,270	)		25.92
	Unvested outstanding at December 31, 2013		230,127			30.43
	The total fair value of shares of restricted stock awards vested for the years ended December 31, 2013, 2012 and 2011 was $3.4 million, $1.0 million and $0, 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, 2013, there was $6.9 million of total unrecognized compensation cost related to restricted stock awards, which is expected to be recognized over a weighted-average period of 2.1 years.
	Restricted Stock Units
	The following table summarizes activity for restricted stock units for the year ended December 31, 2013:
	Restricted Stock			Weighted-
	Units			Average Grant-
				Date Fair
				Value
Unvested outstanding at January 1, 2013		295,737		$	38.76
Granted		97,804			81.12
Vested		(253,384	)		42.53
Forfeited or cancelled		(19,034	)		59.26
Unvested outstanding at December 31, 2013		121,123			64.07
In April 2013, pursuant to the terms of a Restricted Stock Unit Award Notice and Restricted Stock Unit Award Agreement between Zillow and a former employee, 218,071 unvested restricted stock units held by such employee became vested, such that the former employee received one share of Zillow’s Class A common stock for each outstanding restricted stock unit. As a result of the accelerated vesting of the restricted stock units, we recognized approximately $7.1 million of share-based compensation expense during the year ended December 31, 2013, which is included within sales and marketing expense.
In September 2013, pursuant to the terms of a Restricted Stock Unit Award Notice and Restricted Stock Unit Agreement entered into between Zillow and an employee, Zillow granted to the employee restricted stock units for 26,000 shares of our Class A common stock. One twelfth of each restricted stock unit award will vest on each one-month anniversary of the vesting commencement date of September 20, 2013, subject to the recipient’s continued full-time employment or service to Zillow. In the event of termination of service during the first six months of employment by Zillow without cause or upon the resignation by such employee for good reason, 13,000 of the restricted stock units, less the number of restricted stock units that already vested prior to termination, will become vested units, and such employee 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 $2.3 million.
In connection with our acquisition of StreetEasy, in October 2013 we granted restricted stock units for an aggregate 54,929 shares of our Class A common stock to certain former employees of StreetEasy who accepted employment with Zillow. The grant date fair value of the restricted stock units is approximately $4.4 million. In general, each restricted stock unit award will vest in substantially equal installments on each one-month anniversary of the vesting commencement date over a four-year period, subject to the recipient’s continued employment with or service to Zillow.
The total fair value of vested restricted stock units was $10.8 million, $0 million and $0 million, respectively, for the years ended December 31, 2013, 2012 and 2011.
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, 2013, there was $7.8 million of total unrecognized compensation cost related to restricted stock units, which is expected to be recognized over a weighted-average period of 2.78 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,
	2013			2012			2011
Cost of revenue	$	737		$	380		$	189
Sales and marketing		10,969			2,433			388
Technology and development		4,660			1,886			546
General and administrative		7,070			1,912			822
	$	23,436		$	6,611		$	1,945

Net_Income_Loss_Per_Share_Attr

Net Income (Loss) Per Share Attributable to Common Shareholders	12 Months Ended
	Dec. 31, 2013
Earnings Per Share [Abstract]	'
Net Income (Loss) Per Share Attributable to Common Shareholders	'
	Note 12. Net Income (Loss) Per Share Attributable to Common Shareholders
	Basic net income (loss) per share attributable to common shareholders is computed by dividing net income (loss) attributable to common shareholders by the weighted-average number of common shares (including Class A common stock, Class B common stock and Class C common stock) outstanding during the period. In the calculation of basic net income (loss) per share attributable to common shareholders, undistributed earnings are allocated assuming all earnings during the period were distributed. Prior to our IPO in July 2011, net income is first allocated to the Series A, Series B and Series C convertible preferred shareholders, as the convertible preferred stock is a participating security and the preferred shareholders have contractual preferential rights to distributions. For the year ended December 31, 2011, all income was allocated to Series A, Series B and Series C convertible preferred shareholders, and as a result, there was no income attributable to common shareholders.
	Diluted net income (loss) per share attributable to common shareholders is computed by dividing net income (loss) attributable to common shareholders by the weighted-average number of common shares (including Class A common stock, Class B common stock and Class C 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 stock options and Class A common stock underlying unvested restricted stock and restricted stock 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 (loss) per share attributable to common shareholders because they had a dilutive impact (in thousands):
		Year Ended December 31,
		2013		2012		2011
	Class A common stock issuable upon the exercise of stock options		—		2,469		2,490
	Class A common stock underlying unvested restricted stock awards and restricted stock units		—		46		—
	Total Class A common stock equivalents		—		2,515		2,490
	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,
		2013		2012		2011
	Class A common stock issuable upon the exercise of stock options		3,179		—		—
	Class A common stock underlying unvested restricted stock awards		171		—		—
	Total Class A common stock equivalents		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 the preferred stock have been satisfied. We have not presented net income (loss) per share attributable to common shareholders under the two-class method for our Class A common stock, Class B common stock and Class C 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, 2013
Commitments And Contingencies Disclosure [Abstract]	'
Commitments and Contingencies	'
	Note 13. Commitments and Contingencies
	Lease Commitments
	We have various operating leases for office space and equipment. In March 2011, we entered into a lease for approximately 66,000 square feet of office space that houses our corporate headquarters in Seattle, Washington, for which we are obligated to make escalating monthly lease payments that began in December 2012 and continue through November 2022. In June 2012, we entered into a lease amendment for our corporate headquarters in Seattle, Washington, which increased the rentable area of the premises by 21,575 square feet, for which we are obligated to make escalating monthly lease payments that began in January 2013 and continue through November 2022. In April 2013, we entered into a second lease amendment for our corporate headquarters in Seattle, Washington, which increased the rentable area of the premises by 22,583 square feet as of October 1, 2013, and will increase the rentable area of the premises by an additional 22,583 square feet as of September 1, 2014, for which we are obligated to make escalating monthly lease payments beginning in January 2014 and December 2014, respectively, and continuing through November 2022. In April 2012, we entered into an operating lease in Irvine, California for 20,025 square feet under which we are obligated to make escalating monthly lease payments which began in August 2012 and continue through July 2022. In September 2013, we entered into a lease amendment for our operating lease in Irvine, California, which increased the rentable area of the premises by 20,024 square feet, for which we are obligated to make escalating monthly lease payments beginning in February 2014 and continuing 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. We lease additional office space in Chicago, Illinois, Lincoln, Nebraska, and New York, New York.
	Future minimum payments for all operating leases as of December 31, 2013 are as follows (in thousands):
	2014	$	5,353
	2015		7,005
	2016		7,368
	2017		7,446
	2018		7,494
	All future years		23,505
	Total future minimum lease payments	$	58,171
	Rent expense for the years ended December 31, 2013, 2012 and 2011, was $4.1 million, $2.6 million and $2.1 million, respectively.
	Purchase Commitments
	As of December 31, 2013, we had non-cancelable purchase commitments for content related to our mobile applications and websites totaling $13.6 million. The amount due for this content as of December 31, 2013 is as follows (in thousands):
	2014	$	4,546
	2015		4,650
	2016		3,600
	2017		817
	2018 and all future years		—
	Total future purchase commitments	$	13,613
	Line of Credit and Letters of Credit
	During March 2011, we entered into a loan and security agreement with a financial institution to establish a line of credit of $4.0 million. In April 2012, we amended our loan and security agreement to increase our line of credit from $4.0 million to $25.0 million. In September 2013, we terminated the loan and security agreement.
	In March 2011, we executed a standby letter of credit of $1.5 million in connection with the lease of our Seattle, Washington offices, and in July 2012, we amended the standby letter of credit to increase the amount to approximately $1.7 million. In connection with the April 2013 amendment to the lease of our Seattle, Washington offices, we amended our standby letter of credit to increase the amount from approximately $1.7 million to approximately $2.0 million. The letter of credit is secured by our investments and is 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 seeks, among other things, a judgment that we have infringed certain patents held by Smarter Agent, an injunctive order against the alleged infringing activities and an 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. 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 August 26, 2013, we acquired StreetEasy, including the Smarter Agent complaint against StreetEasy. On December 14, 2012, we acquired HotPads, including the Smarter Agent complaint against HotPads. We have not recorded an accrual related to these complaints as of December 31, 2013 or 2012, as we do not believe a material loss is probable. It is a reasonable possibility that a loss may be incurred; however, the possible loss or range of loss is not estimable.
	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 seeks, among other things, a judgment that we have infringed certain patents held by LendingTree, an injunctive order against the alleged infringing activities and an award for damages. We have denied the allegations and asserted counterclaims seeking declarations that we are not infringing the patents and that the patents are unenforceable and invalid. The LendingTree matter currently is subject to a trial by jury that began on February 10, 2014. We have not recorded an accrual related to this complaint as of December 31, 2013 or 2012, as we do not believe a material loss is probable. It is a reasonable possibility that a loss may be incurred; however, the possible loss or range of loss is not estimable.
	In November 2012, a securities class action lawsuit was filed against us and certain of our executive officers seeking unspecified damages in the U.S. District Court for the Western District of Washington at Seattle. 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. A consolidated amended complaint was filed in June 2013. In general, the complaint 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. That motion to dismiss is pending. We intend to deny the allegations of any wrongdoing and vigorously defend the claims in the lawsuit. We have not recorded an accrual related to this lawsuit as of December 31, 2013 or 2012, as we do not believe a material loss is probable. It is a reasonable possibility that a loss may be incurred; however, the possible loss or range of loss is not estimable.
	In January 2013, a shareholder derivative lawsuit was filed against certain of our executive officers and directors seeking unspecified damages on behalf of Zillow in the U.S. District Court for the Western District of Washington at Seattle. In general, the complaint alleged, among other things, that the defendants breached their fiduciary obligations owed to Zillow, and that as a result of the breach of such fiduciary duties, Zillow wasted corporate assets defending itself in the securities class action lawsuit described above, and that defendants were unjustly enriched by selling shares of our common stock on the basis of knowledge of adverse trends before such information was publicly disclosed. The shareholder derivative lawsuit was dismissed without prejudice on September 26, 2013, and we therefore have not recorded an accrual related to this lawsuit as of December 31, 2013 or 2012.
	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, 2013
Segment Reporting [Abstract]	'
Segment Information and Revenue	'
	Note 14. 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,
		2013		2012		2011
	Marketplace revenue:
	Real estate	$	132,396	$	75,900	$	36,749
	Mortgages		21,812		10,770		5,441
	Total Marketplace revenue		154,208		86,670		42,190
	Display revenue		43,337		30,180		23,863
	Total revenue	$	197,545	$	116,850	$	66,053

Subsequent_Events

Subsequent Events	12 Months Ended
	Dec. 31, 2013
Subsequent Events [Abstract]	'
Subsequent Events	'
	Note 15. Subsequent Events
	In January 2014, we amended our operating lease for our principal offices in Seattle, Washington, to increase the rentable area of the premises by 22,694 square feet as of October 1, 2016, for which we are obligated to make escalating monthly lease payments beginning in January 2017 and continuing through November 2022. Future minimum payments for the additional space are as follows (in thousands):
	Remainder of 2014	$	—
	2015		—
	2016		—
	2017		955
	2018		978
	All future years		4,047
	Total future minimum lease payments	$	5,980

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Basis of Presentation	'
	Basis of Presentation
	These 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. Estimates are used for 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. 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.
Prior Period Adjustments	'
	Prior Period Adjustments
	The balance sheet as of December 31, 2012 has been revised to correct an immaterial error in the presentation of property and equipment, net and current and noncurrent deferred rent, which were understated by equal amounts of $3.3 million, related to leasehold improvements made that were funded by landlord allowances. The statement of cash flows for the year ended December 31, 2012 has been revised to correct the immaterial error in net cash provided by operating activities and net cash used in investing activities, which were understated by equal amounts of $3.3 million.
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, commercial paper, and corporate notes and bonds. 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.
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 five to 7.5 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 but unrecognized subscription revenue, 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, primarily on an individual subscription basis, and mortgage professionals and brand advertisers. Our two revenue categories are marketplace revenue and display revenue.
	Marketplace Revenue. Marketplace revenue consists of real estate revenue and mortgages revenue. Real estate revenue primarily includes subscriptions sold to real estate agents under our Premier Agent program, as well as revenue generated by Zillow Rentals. Mortgages revenue primarily includes Zillow Mortgage Marketplace advertising sold to mortgage lenders on a cost-per-click, or CPC, basis. Mortgages revenue also includes revenue generated by Mortech, a company we acquired in November 2012 that 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 original flagship subscription 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 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 customers for our Platinum Premier Agent subscription product based on the number of impressions delivered on our buyer’s agent list in zip codes purchased. Our Platinum Premier Agent subscription 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 subscription 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, which is typically over a period of six 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 Mortgage Marketplace, 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 Mortgage Marketplace 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 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, 2013, 2012 or 2011.
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 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, 2013, 2012 and 2011, expenses attributable to research and development for our business totaled $41.7 million, $22.0 million and $10.7 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 stock options. In valuing our options, 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 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 options as the average of the vesting option 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 share options. 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 stock options 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 and restricted stock 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, 2013, 2012 and 2011, expenses attributable to advertising totaled $38.7 million, $11.1 million and $4.0 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 July 2013, the Financial Accounting Standards Board (“FASB”) issued guidance on the presentation of certain unrecognized tax benefits in the financial statements. This guidance provides that a liability related to an unrecognized tax benefit must be offset against a deferred tax asset for a net operating loss carryforward, a similar tax loss or a tax credit carryforward if such settlement is required or expected in the event the uncertain tax position is disallowed. This guidance is effective for interim and annual reporting periods beginning after December 15, 2013, with earlier adoption permitted, and may be applied prospectively or retrospectively. We expect to adopt this guidance on January 1, 2014. The adoption of this guidance is not expected to have a significant impact on our financial position, results of operations or cash flows, as we have provided a full valuation allowance against our net deferred tax assets.
	In February 2013, the FASB issued guidance on the reporting of amounts reclassified out of accumulated other comprehensive income. An entity must report the effect of significant reclassifications out of accumulated other comprehensive income on the respective line items in net income if the amount being reclassified is required under GAAP to be reclassified in its entirety to net income. For other amounts that are not required under GAAP to be reclassified in their entirety to net income in the same reporting period, an entity is required to cross-reference other disclosures required under GAAP that provide additional detail about those amounts. This guidance is effective for interim and annual reporting periods beginning after December 15, 2012, with earlier adoption permitted, and must be applied prospectively. We adopted this guidance on January 1, 2013. The adoption of this guidance did not have any impact on our financial position, results of operations or cash flows, as we do not have any items of other comprehensive income in any period presented.
	In June 2011, the FASB issued guidance on the presentation of comprehensive income to increase the prominence of other comprehensive income in the financial statements. An entity has the option to present the components of net income and comprehensive income in either one or two consecutive financial statements. This guidance is effective for interim and annual reporting periods beginning after December 15, 2011, with earlier adoption permitted, and must be applied retrospectively. We adopted this guidance on January 1, 2012. The adoption of this guidance did not have any impact on our financial position, results of operations or cash flows as we do not have any items of other comprehensive income in any period presented, and therefore, we are not required to report other comprehensive income or comprehensive income.
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, therefore, these assets are recorded at fair value on a recurring basis and classified as Level 1 in the fair value hierarchy.
	Short-term and long-term investments—Our investments consist of fixed income securities, which include U.S. government agency securities, commercial paper, and corporate notes and bonds. 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. Our U.S. government agency securities are classified as Level 1 in the fair value hierarchy. Our commercial paper and corporate notes and bonds are classified as Level 2 in the fair value hierarchy.
Net Income (Loss) Per Share	'
	Basic net income (loss) per share attributable to common shareholders is computed by dividing net income (loss) attributable to common shareholders by the weighted-average number of common shares (including Class A common stock, Class B common stock and Class C common stock) outstanding during the period. In the calculation of basic net income (loss) per share attributable to common shareholders, undistributed earnings are allocated assuming all earnings during the period were distributed. Prior to our IPO in July 2011, net income is first allocated to the Series A, Series B and Series C convertible preferred shareholders, as the convertible preferred stock is a participating security and the preferred shareholders have contractual preferential rights to distributions. For the year ended December 31, 2011, all income was allocated to Series A, Series B and Series C convertible preferred shareholders, and as a result, there was no income attributable to common shareholders.
	Diluted net income (loss) per share attributable to common shareholders is computed by dividing net income (loss) attributable to common shareholders by the weighted-average number of common shares (including Class A common stock, Class B common stock and Class C 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 stock options and Class A common stock underlying unvested restricted stock and restricted stock 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, 2013
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, 2013
Fair Value Disclosures [Abstract]	'
Fair Value Measurements of Assets on Recurring Basis	'
	The following tables present the balances of assets measured at fair value on a recurring basis as of the dates presented (in thousands):
		December 31, 2013
		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
		December 31, 2012
		Total		Level 1		Level 2
	Cash equivalents:
	Money market funds	$	143,246	$	143,246	$	—
	Short-term investments:
	U.S government agency securities		26,085		26,085		—
	Commercial paper		16,965		—		16,965
	Corporate notes and bonds		1,004		—		1,004
	Long-term investments:
	U.S government agency securities		7,079		7,079		—
	Corporate notes and bonds		2,310		—		2,310
	Total	$	196,689	$	176,410	$	20,279

Accounts_Receivable_Net_Tables

Accounts Receivable, Net (Tables)	12 Months Ended
	Dec. 31, 2013
Receivables [Abstract]	'
Accounts Receivable	'
	The following table presents the detail of accounts receivable as of the dates presented (in thousands):
		December 31,
		2013			2012
	Accounts receivable	$	13,793		$	9,503
	Unbilled accounts receivable		3,291			117
	Less: allowance for doubtful accounts		(1,850	)		(965	)
	Accounts receivable, net	$	15,234		$	8,655
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,
		2013			2012			2011
	Allowance for doubtful accounts:
	Balance, beginning of period	$	965		$	683		$	501
	Additions charged to expense		1,907			1,227			594
	Less: write-offs, net of recoveries and other adjustments		(1,022	)		(945	)		(412	)
	Balance, end of period	$	1,850		$	965		$	683

Property_and_Equipment_Net_Tab

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2013
Property Plant And Equipment [Abstract]	'
Details of Property and Equipment	'
	The following table presents the detail of property and equipment as of the dates presented (in thousands):
		December 31,
		2013			2012
	Website development costs	$	50,408		$	33,448
	Computer equipment		8,238			8,380
	Leasehold improvements		7,320			4,145
	Software		1,807			1,209
	Construction-in-progress		3,289			3,093
	Office equipment, furniture and fixtures		3,661			2,186
	Property and equipment		74,723			52,461
	Less: accumulated amortization and depreciation		(47,315	)		(35,513	)
	Property and equipment, net	$	27,408		$	16,948

Acquisitions_Tables

Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2013
Business Combinations [Abstract]	'
Summary of Purchase Price	'
	The purchase price was approximately $48.2 million, as summarized in the following table (in thousands):
	Cash payable for the outstanding stock of StreetEasy	$	42,821
	Cash payable for the cancellation of vested options to purchase shares of StreetEasy’s common stock		2,989
	Certain transaction expenses and other costs incurred by StreetEasy		1,924
	Substituted unvested stock options attributable to pre-combination service		430
	Total purchase price	$	48,164
Identifiable Intangible Assets Acquired	'
	Identifiable intangible assets acquired consisted of the following (in thousands):
					Estimated
					Amortization
					Period
					(in years)
	Developed technology	$	4,500			5
	Customer relationships		4,900			5
	Trademarks		2,200			5
	Total intangible assets acquired	$	11,600
Purchase Price Allocation	'
	Based upon the fair values determined by us, in which we considered or relied in part upon a valuation report of a third-party expert, the total purchase price was allocated as follows (in thousands):
	Accounts receivable	$	917
	Prepaid expenses and other current assets		191
	Property and equipment		1,138
	Other identifiable tangible assets		144
	Total tangible assets		2,390
	Accounts payable		(72	)
	Accrued expenses and other current liabilities		(175	)
	Accrued compensation and benefits		(223	)
	Other identifiable liabilities		(174	)
	Net deferred tax liability		(4,111	)
	Total liabilities		(4,755	)
	Net acquired liabilities		(2,365	)
	Identifiable intangible assets		11,600
	Goodwill		38,929
	Total purchase price allocation	$	48,164
Pro Forma Condensed Combined Financial Information	'
	The following table presents the unaudited pro forma condensed combined financial information (in thousands, except per share amounts):
		Year Ended
		December  31,
		2013			2012
	Revenue	$	202,086		$	122,547
	Net income (loss)	$	(14,121	)	$	4,940
	Net income (loss) per share—basic	$	(0.39	)	$	0.16
	Net income (loss) per share—diluted	$	(0.39	)	$	0.15

Goodwill_Tables

Goodwill (Tables)	12 Months Ended
	Dec. 31, 2013
Goodwill And Intangible Assets Disclosure [Abstract]	'
Change in Goodwill	'
	The following table presents the change in goodwill from December 31, 2012 through December 31, 2013 (in thousands):
	Balance as of December 31, 2012	$	54,284
	Goodwill recorded in connection with the acquisition of StreetEasy		38,929
	Balance as of December 31, 2013	$	93,213

Intangible_Assets_Tables

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2013
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, 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
		December 31, 2012
		Cost		Accumulated			Net
				Amortization
	Purchased content	$	9,044	$	(6,015	)	$	3,029
	Developed technology		14,335		(1,534	)		12,801
	Customer relationships		4,875		(387	)		4,488
	Trademarks		1,061		(131	)		930
	Total	$	29,315	$	(8,067	)	$	21,248
Estimated Future Amortization Expense for Intangible Assets	'
	Estimated future amortization expense for intangible assets, including amortization related to future commitments, as of December 31, 2013 is as follows (in thousands):
	2014	$	10,341
	2015		10,074
	2016		9,074
	2017		7,343
	2018		4,935
	All future years		1,261
	Total	$	43,028

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2013
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,
		2013			2012			2011
	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,
		2013			2012			2011
	Tax expense at federal statutory rate		(34.0	%)		34	%		34	%
	State income taxes, net of federal tax benefit		(5.8	%)		0	%		0	%
	Nondeductible expenses		3.1	%		9.2	%		10	%
	Share-based compensation		0.2	%		3.5	%		37.1	%
	Research and development credits		(23.3	%)		0	%		(32.6	%)
	Valuation allowance		35	%		(46.7	%)		(48.5	%)
	Effective tax rate		(24.8	%)		0	%		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,
		2013			2012
	Deferred tax assets:
	Federal and state net operating loss carryforwards	$	24,152		$	19,899
	Share-based compensation		4,467			2,712
	Goodwill		1,776			591
	Start-up and organizational costs		491			554
	Research and development credits		5,123			1,255
	Accruals and reserves		901			792
	Other		3,415			1,606
	Total deferred tax assets		40,325			27,409
	Deferred tax liabilities:
	Website and software development costs		(4,927	)		(2,934	)
	Intangibles		(6,519	)		(3,037	)
	Depreciation and amortization		(1,579	)		(67	)
	Net deferred tax assets before valuation allowance		27,300			21,371
	Less: valuation allowance		(27,300	)		(21,371	)
	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, 2011	$	866
	Gross increases—current-period tax positions		359
	Balance at December 31, 2011	$	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

Shareholders_Equity_Tables

Shareholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2013
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,
		2013		2012
	Class A common stock options outstanding		5,156,706		5,462,672
	Class A common stock available for grant under equity plan		1,513,264		306,535
	Restricted stock units outstanding		121,123		296,004
	Shares issuable upon conversion of outstanding Class B common stock		6,468,892		7,462,526
	Total		13,259,985		13,527,737

ShareBased_Awards_Tables

Share-Based Awards (Tables)	12 Months Ended
	Dec. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
Summary of Stock Option Activity	'
	The following table summarizes stock option activity for the year ended December 31, 2013:
		Shares			Number of			Weighted-			Weighted-		Aggregate
		Available			Shares			Average			Average		Intrinsic
		for Grant			Subject to			Exercise			Remaining		Value
					Existing			Price Per			Contractual
					Options			Share			Life (Years)
	Outstanding at January 1, 2013		321,678			5,462,672		$	14.48			4.88	$	78,912,364
	Authorized increase in plan shares		2,887,064			—			—
	Granted		(1,984,157	)		2,009,542			43.87
	Exercised		—			(2,026,829	)		9.03
	Forfeited or cancelled		288,679			(288,679	)		31.93
	Outstanding at December 31, 2013		1,513,264			5,156,706			27.09			5.43		283,008,505
	Vested and exercisable at December 31, 2013					1,575,015			12.02			3.93		109,787,836
Fair Value of Options Granted, Excluding Non Employee Director Awards, Estimated at Date of Grant Using Black Scholes Merton Option Pricing Model	'
	The fair value of options granted, excluding Nonemployee Director Awards and the Executive Awards, 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,
		2013			2012			2011
	Expected volatility		50% – 54	%		49% – 52	%		49% – 52	%
	Expected dividend yields		—			—			—
	Average risk-free interest rate		0.70% – 1.27	%		0.53% – 0.76	%		0.79% – 1.87	%
	Weighted-average expected life		4.58 years			4.58 years			4.58 years
	Weighted-average fair value of options granted	$	21.26		$	13.79		$	4.66
Summary of Stock Options Outstanding and Vested and Exercisable Stock Options	'
	The following table summarizes information about options outstanding and vested and exercisable stock options as of December 31, 2013:
		Options Outstanding									Options Vested and Exercisable
	Exercise Price or Range	Number			Weighted-			Weighted Average			Number		Weighted
		Outstanding			Average			Exercise Price			Exercisable		Average  Exercise
					Remaining								Price
					Contractual Life
					(Years)
	$0.08 – $3.85		839,063			3.24		$	3.43			706,969	$	3.47
	$3.89 – $5.98		683,918			4.15			3.89			341,559		3.89
	$6.32 – $29.50		830,733			5.58			25.38			173,466		20.26
	$29.69 – $30.46		527,311			5.07			30.4			177,099		30.38
	$30.60 – $36.30		284,158			5.15			32.12			112,581		31.41
	$36.36		1,393,635			7.14			36.36			2,013		36.36
	$36.72 – $89.09		518,204			6.24			57.18			61,328		42.52
	$90.05 – $96.24		65,328			6.59			94.84			—		—
	$96.25		13,756			6.69			96.25			—		—
	$99.09		600			6.67			99.09			—		—
	Total		5,156,706			5.43			27.09			1,575,015		12.02
Summary of Restricted Stock Award Activity	'
	The following table summarizes restricted stock award activity for the year ended December 31, 2013:
		Shares of			Weighted-
		Restricted Stock			Average Grant-
					Date Fair
					Value
	Unvested outstanding at January 1, 2013		340,103		$	30.37
	Granted		3,673			44.66
	Vested		(108,379	)		30.94
	Forfeited or cancelled		(5,270	)		25.92
	Unvested outstanding at December 31, 2013		230,127			30.43
Summary of Restricted Stock Units Activity	'
	The following table summarizes activity for restricted stock units for the year ended December 31, 2013:
		Restricted Stock			Weighted-
		Units			Average Grant-
					Date Fair
					Value
	Unvested outstanding at January 1, 2013		295,737		$	38.76
	Granted		97,804			81.12
	Vested		(253,384	)		42.53
	Forfeited or cancelled		(19,034	)		59.26
	Unvested outstanding at December 31, 2013		121,123			64.07
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,
		2013			2012			2011
	Cost of revenue	$	737		$	380		$	189
	Sales and marketing		10,969			2,433			388
	Technology and development		4,660			1,886			546
	General and administrative		7,070			1,912			822
		$	23,436		$	6,611		$	1,945

Net_Income_Loss_Per_Share_Attr1

Net Income (Loss) Per Share Attributable to Common Shareholders (Tables)	12 Months Ended
	Dec. 31, 2013
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 (loss) per share attributable to common shareholders because they had a dilutive impact (in thousands):
		Year Ended December 31,
		2013		2012		2011
	Class A common stock issuable upon the exercise of stock options		—		2,469		2,490
	Class A common stock underlying unvested restricted stock awards and restricted stock units		—		46		—
	Total Class A common stock equivalents		—		2,515		2,490
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,
		2013		2012		2011
	Class A common stock issuable upon the exercise of stock options		3,179		—		—
	Class A common stock underlying unvested restricted stock awards		171		—		—
	Total Class A common stock equivalents		3,350		—		—

Subsequent_Events_Tables

Subsequent Events (Tables)	12 Months Ended
	Dec. 31, 2013
Future Minimum Operating Lease Payments	'
	Future minimum payments for all operating leases as of December 31, 2013 are as follows (in thousands):
	2014	$	5,353
	2015		7,005
	2016		7,368
	2017		7,446
	2018		7,494
	All future years		23,505
	Total future minimum lease payments	$	58,171
Seattle, Washington	'
Future Minimum Operating Lease Payments	'
	Future minimum payments for the additional space are as follows (in thousands):
	Remainder of 2014	$	—
	2015		—
	2016		—
	2017		955
	2018		978
	All future years		4,047
	Total future minimum lease payments	$	5,980

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2013
Commitments And Contingencies Disclosure [Abstract]	'
Purchase Commitments for Content Related to Mobile Applications and Websites	'
	The amount due for this content as of December 31, 2013 is as follows (in thousands):
	2014	$	4,546
	2015		4,650
	2016		3,600
	2017		817
	2018 and all future years		—
	Total future purchase commitments	$	13,613

Segment_Information_and_Revenu1

Segment Information and Revenue (Tables)	12 Months Ended
	Dec. 31, 2013
Segment Reporting [Abstract]	'
Revenue Categories	'
	The following table presents our revenue categories during the periods presented (in thousands):
		Year Ended December 31,
		2013		2012		2011
	Marketplace revenue:
	Real estate	$	132,396	$	75,900	$	36,749
	Mortgages		21,812		10,770		5,441
	Total Marketplace revenue		154,208		86,670		42,190
	Display revenue		43,337		30,180		23,863
	Total revenue	$	197,545	$	116,850	$	66,053

Summary_of_Significant_Account3

Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
	Customer	Customer	Customer
	Categories
Schedule Of Significant Accounting Policies [Line Items]	'	'	'
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	$41.70	$22	$10.70
Advertising expense	38.7	11.1	4
Software Development	'	'	'
Schedule Of Significant Accounting Policies [Line Items]	'	'	'
Amortization period	'1 year	'	'
Balance sheet	'	'	'
Schedule Of Significant Accounting Policies [Line Items]	'	'	'
Immaterial error correction, amount	3.3	'	'
Cash flows	'	'	'
Schedule Of Significant Accounting Policies [Line Items]	'	'	'
Immaterial error correction, amount	$3.30	'	'
Minimum | Customer Concentration Risk | Sales Revenue, Net	'	'	'
Schedule Of Significant Accounting Policies [Line Items]	'	'	'
Percentage of revenue	10.00%	10.00%	10.00%
Purchased Content | Minimum	'	'	'
Schedule Of Significant Accounting Policies [Line Items]	'	'	'
Amortization period	'5 years	'	'
Purchased Content | Maximum	'	'	'
Schedule Of Significant Accounting Policies [Line Items]	'	'	'
Amortization period	'7 years 6 months	'	'

Useful_Lives_Detail

Useful Lives (Detail)	12 Months Ended
	Dec. 31, 2013
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

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012
		Mature in 2014	Mature in 2015	Fair Value, Inputs, Level 3	Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'	'	'	'
Original maturities date of money market funds	'Less than three months	'	'	'	'
Investment Maturity, Percentage	'	39.60%	60.40%	'	'
Investment Maturity, Year	'	'2014	'2015	'	'
Assets measured at fair value on recurring basis	'	'	'	$0	$0
Liabilities measured at fair value on recurring basis	'	'	'	$0	$0

Fair_Value_Measurement_of_Asse

Fair Value Measurement of Assets on Recurring Basis (Detail) (Fair Value, Measurements, Recurring, USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total	$424,213	$196,689
Money Market Funds	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Cash equivalents	184,941	143,246
U.S government agency securities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Cash equivalents	3,306	'
Short-term investments	78,448	26,085
Long-term investments	112,623	7,079
Commercial Paper	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Short-term investments	3,998	16,965
Corporate Notes and Bonds	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Short-term investments	11,085	1,004
Long-term investments	29,812	2,310
Fair Value, Inputs, Level 1	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total	379,318	176,410
Fair Value, Inputs, Level 1 | Money Market Funds	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Cash equivalents	184,941	143,246
Fair Value, Inputs, Level 1 | U.S government agency securities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Cash equivalents	3,306	'
Short-term investments	78,448	26,085
Long-term investments	112,623	7,079
Fair Value, Inputs, Level 1 | Commercial Paper	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Short-term investments	'	'
Fair Value, Inputs, Level 1 | Corporate Notes and Bonds	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Short-term investments	'	'
Long-term investments	'	'
Fair Value, Inputs, Level 2	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total	44,895	20,279
Fair Value, Inputs, Level 2 | Money Market Funds	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Cash equivalents	'	'
Fair Value, Inputs, Level 2 | U.S government agency securities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Cash equivalents	'	'
Short-term investments	'	'
Long-term investments	'	'
Fair Value, Inputs, Level 2 | Commercial Paper	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Short-term investments	3,998	16,965
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	11,085	1,004
Long-term investments	$29,812	$2,310

Accounts_Receivable_Detail

Accounts Receivable (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
In Thousands, unless otherwise specified
Receivables [Abstract]	'	'	'	'
Accounts receivable	$13,793	$9,503	'	'
Unbilled accounts receivable	3,291	117	'	'
Less: allowance for doubtful accounts	-1,850	-965	-683	-501
Accounts receivable, net	$15,234	$8,655	'	'

Allowance_for_Doubtful_Account

Allowance for Doubtful Accounts (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Allowance for doubtful accounts:	'	'	'
Balance, beginning of period	$965	$683	$501
Additions charged to expense	1,907	1,227	594
Less: write-offs, net of recoveries and other adjustments	-1,022	-945	-412
Balance, end of period	$1,850	$965	$683

Detail_of_Property_and_Equipme

Detail of Property and Equipment (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	$74,723	$52,461
Less: accumulated amortization and depreciation	-47,315	-35,513
Property and equipment, net	27,408	16,948
Website development costs	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	50,408	33,448
Computer equipment	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	8,238	8,380
Leasehold improvements	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	7,320	4,145
Software	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	1,807	1,209
Construction-in-progress	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	3,289	3,093
Office equipment, furniture and fixtures	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	$3,661	$2,186

Property_and_Equipment_Net_Add

Property and Equipment, Net - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]	'	'	'
Amortization and depreciation expense related to property and equipment other than website development costs	$3,500,000	$1,600,000	$1,800,000
Capitalization of website development costs	17,300,000	11,500,000	5,500,000
Amortization expense for website development costs included in technology and development expenses	19,791,000	11,179,000	5,384,000
Technology and Development	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'
Amortization expense for website development costs included in technology and development expenses	7,600,000	4,300,000	1,300,000
Technology and Development | Website development costs	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'
Amortization expense for website development costs included in technology and development expenses	$12,200,000	$6,900,000	$4,100,000

Acquisition_Additional_Informa

Acquisition - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Aug. 26, 2013
Maximum	'	'
Business Acquisition [Line Items]	'	'
Estimates and assumptions related to the purchase price allocation	'1 year	'
StreetEasy, Inc.	'	'
Business Acquisition [Line Items]	'	'
Cash paid for outstanding stock	'	$42,821,000
Consideration deposited in escrow	'	5,000,000
Accrued expenses and other current liabilities in connection with acquisition	5,500,000	'
Prepaid expenses and other current assets	500,000	191,000
Total purchase price	'	48,164,000
Acquisition-related expenses	$400,000	'

Summary_of_Purchase_Price_Deta

Summary of Purchase Price (Detail) (StreetEasy, Inc., USD $)	Aug. 26, 2013
In Thousands, unless otherwise specified
StreetEasy, Inc.	'
Business Acquisition [Line Items]	'
Cash payable for the outstanding stock of StreetEasy	$42,821
Cash payable for the cancellation of vested options to purchase shares of StreetEasy's common stock	2,989
Certain transaction expenses and other costs incurred by StreetEasy	1,924
Substituted unvested stock options attributable to pre-combination service	430
Total purchase price	$48,164

Identifiable_Intangible_Assets

Identifiable Intangible Assets Acquired (Detail) (USD $)	1 Months Ended
In Thousands, unless otherwise specified	Aug. 26, 2013
Finite-Lived Intangible Assets [Line Items]	'
Intangible assets acquired	$11,600
StreetEasy, Inc. | Developed Technology	'
Finite-Lived Intangible Assets [Line Items]	'
Intangible assets acquired	4,500
Estimated Amortization Period (in years)	'5 years
StreetEasy, Inc. | Customer Relationships	'
Finite-Lived Intangible Assets [Line Items]	'
Intangible assets acquired	4,900
Estimated Amortization Period (in years)	'5 years
StreetEasy, Inc. | Trademarks	'
Finite-Lived Intangible Assets [Line Items]	'
Intangible assets acquired	$2,200
Estimated Amortization Period (in years)	'5 years

Purchase_Price_Allocation_Deta

Purchase Price Allocation (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Aug. 26, 2013
In Thousands, unless otherwise specified			StreetEasy, Inc.	StreetEasy, Inc.
Business Acquisition [Line Items]	'	'	'	'
Accounts receivable	'	'	'	$917
Prepaid expenses and other current assets	'	'	500	191
Property and equipment	'	'	'	1,138
Other identifiable tangible assets	'	'	'	144
Total tangible assets	'	'	'	2,390
Accounts payable	'	'	'	-72
Accrued expenses and other current liabilities	'	'	'	-175
Accrued compensation and benefits	'	'	'	-223
Other identifiable liabilities	'	'	'	-174
Net deferred tax liability	'	'	'	-4,111
Total liabilities	'	'	'	-4,755
Net acquired liabilities	'	'	'	-2,365
Identifiable intangible assets	'	'	'	11,600
Goodwill	93,213	54,284	'	38,929
Total purchase price	'	'	'	$48,164

Pro_Forma_Condensed_Combined_F

Pro Forma Condensed Combined Financial Information (Detail) (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Business Combinations [Abstract]	'	'
Revenue	$202,086	$122,547
Net income (loss)	($14,121)	$4,940
Net income (loss) per share-basic	($0.39)	$0.16
Net income (loss) per share-diluted	($0.39)	$0.15

Change_in_Goodwill_Detail

Change in Goodwill (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013
Goodwill And Intangible Assets Disclosure [Abstract]	'
Balance as of December 31, 2012	$54,284
Goodwill recorded in connection with the acquisition of StreetEasy	38,929
Balance as of December 31, 2013	$93,213

Intangible_Assets_Detail

Intangible Assets (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Finite-Lived Intangible Assets [Line Items]	'	'
Cost	$44,839	$29,315
Accumulated Amortization	-15,690	-8,067
Net	29,149	21,248
Purchased Content	'	'
Finite-Lived Intangible Assets [Line Items]	'	'
Cost	12,968	9,044
Accumulated Amortization	-8,846	-6,015
Net	4,122	3,029
Developed Technology	'	'
Finite-Lived Intangible Assets [Line Items]	'	'
Cost	18,835	14,335
Accumulated Amortization	-4,417	-1,534
Net	14,418	12,801
Customer Relationships	'	'
Finite-Lived Intangible Assets [Line Items]	'	'
Cost	9,775	4,875
Accumulated Amortization	-1,799	-387
Net	7,976	4,488
Trademarks	'	'
Finite-Lived Intangible Assets [Line Items]	'	'
Cost	3,261	1,061
Accumulated Amortization	-628	-131
Net	$2,633	$930

Intangible_Assets_Additional_I

Intangible Assets - Additional Information (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
	Y	Y
Finite-Lived Intangible Assets [Line Items]	'	'	'
Amortization of website development costs and intangible assets	$19,791	$11,179	$5,384
Remaining weighted-average amortization period	4.5	4.9	'
Technology and Development	'	'	'
Finite-Lived Intangible Assets [Line Items]	'	'	'
Amortization of website development costs and intangible assets	$7,600	$4,300	$1,300

Estimated_Future_Amortization_

Estimated Future Amortization Expenses for Intangible Assets (Detail) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Goodwill And Intangible Assets Disclosure [Abstract]	'
2014	$10,341
2015	10,074
2016	9,074
2017	7,343
2018	4,935
All future years	1,261
Total	$43,028

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule Of Income Tax [Line Items]	'	'	'
Income tax liability	$0	$0	$0
Income tax expense	0	0	0
Income tax benefit, acquisition	4,111,000	'	'
Minimum estimated percentage of deferred tax unrealized	50.00%	'	'
Increase/decrease in valuation allowance	5,900,000	3,600,000	'
Income tax year open for audit	'Tax years from 2010 through 2013 are currently open for audit by federal and state taxing authorities.	'	'
Unrecognized income tax accrued interest and penalties	0	'	'
Share Based Compensation Liability	'	'	'
Schedule Of Income Tax [Line Items]	'	'	'
Net operating loss carryforwards	167,900,000	'	'
Research And Development	'	'	'
Schedule Of Income Tax [Line Items]	'	'	'
Net operating loss carryforwards	5,100,000	1,300,000	'
Tax credit carryforwards expiration year	'2025	'	'
Change in unrecognized tax benefits period	'12 months	'	'
Federal	'	'	'
Schedule Of Income Tax [Line Items]	'	'	'
Net operating loss carryforwards	236,500,000	115,700,000	'
State	'	'	'
Schedule Of Income Tax [Line Items]	'	'	'
Net operating loss carryforwards	$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	Dec. 31, 2012	Dec. 31, 2011
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, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]	'	'	'
Tax expense at federal statutory rate	-34.00%	34.00%	34.00%
State income taxes, net of federal tax benefit	-5.80%	0.00%	0.00%
Nondeductible expenses	3.10%	9.20%	10.00%
Share-based compensation	0.20%	3.50%	37.10%
Research and development credits	-23.30%	0.00%	-32.60%
Valuation allowance	35.00%	-46.70%	-48.50%
Effective tax rate	-24.80%	0.00%	0.00%

Deferred_Tax_Assets_and_Liabil

Deferred Tax Assets and Liabilities (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Deferred tax assets:	'	'
Federal and state net operating loss carryforwards	$24,152	$19,899
Share-based compensation	4,467	2,712
Goodwill	1,776	591
Start-up and organizational costs	491	554
Research and development credits	5,123	1,255
Accruals and reserves	901	792
Other	3,415	1,606
Total deferred tax assets	40,325	27,409
Deferred tax liabilities:	'	'
Website and software development costs	-4,927	-2,934
Intangibles	-6,519	-3,037
Depreciation and amortization	-1,579	-67
Net deferred tax assets before valuation allowance	27,300	21,371
Less: valuation allowance	-27,300	-21,371
Net deferred tax assets	'	'

Changes_in_Unrecognized_Tax_Be

Changes in Unrecognized Tax Benefits (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]	'	'	'
Unrecognized tax benefits beginning balance	$1,255	$1,225	$866
Gross increases-prior and current-period tax positions	3,868	'	'
Gross increases-prior-period tax positions	'	30	'
Gross increases-current-period tax positions	'	'	359
Unrecognized tax benefits ending balance	$5,123	$1,255	$1,225

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, 2013	Dec. 31, 2012	Dec. 31, 2011
			Vote
Class of Stock [Line Items]	'	'	'	'	'
Number of common stock converted	'	'	993,634	'	'
Net proceeds from issuance of common stock	253.9	156.7	'	'	'
Class A Common Stock	'	'	'	'	'
Class of Stock [Line Items]	'	'	'	'	'
Conversion of convertible preferred stock to Class A common stock in connection with initial public offering	'	'	9,276,190	'	9,276,190
Conversion of Class C common stock to Class A common stock in connection with initial public offering	'	'	2,305,980	'	2,305,980
Common stock holders voting right	'	'	1	'	'
Conversion of common stock conversion ratio	'	'	1	'	'
Number of common stock converted	'	'	993,634	2,065,787	'
Issuance of Class A common stock, shares	3,253,522	3,844,818	'	'	'
Class A Common Stock | Underwriters	'	'	'	'	'
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	'	'	-993,634	-2,065,787	'

Class_A_Common_Stock_Reserved_

Class A Common Stock Reserved for Future Issuance (Detail)	Dec. 31, 2013	Dec. 31, 2012
Class of Stock [Line Items]	'	'
Total	13,259,985	13,527,737
Class B Common Stock	'	'
Class of Stock [Line Items]	'	'
Shares issuable upon conversion of outstanding Class B common stock	6,468,892	7,462,526
Stock Options	'	'
Class of Stock [Line Items]	'	'
Class A common stock options outstanding	5,156,706	5,462,672
Class A common stock available for grant under equity plan	1,513,264	306,535
Restricted Stock Units	'	'
Class of Stock [Line Items]	'	'
Restricted stock units outstanding	121,123	296,004

ShareBased_Awards_Additional_I

Share-Based Awards - Additional Information (Detail) (USD $)

1 Months Ended

12 Months Ended

12 Months Ended

3 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

Apr. 30, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

31-May-13

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Mar. 31, 2013

Dec. 31, 2013

Sep. 30, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Sep. 30, 2013

Apr. 30, 2013

Oct. 31, 2013

Oct. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Chief Executive Officer

Portion One

Portion One

Portion One

Portion Two

Portion Two

Portion Two

StreetEasy, Inc.

HotPads, Inc.

Non Employee Director Rewards

Non Employee Director Rewards

Restricted Stock Units

Restricted Stock Units

Restricted Stock Units

Restricted Stock Units

Restricted Stock Units

Restricted Stock Units

Restricted Stock Units

Restricted Stock Units

Stock Options

Stock Options

Stock Options

Stock Options

Restricted Stock

Restricted Stock

Restricted Stock

2011 Plan

Chief Executive Officer

Chief Executive Officer

Chief Executive Officer

Chief Executive Officer

Chief Executive Officer

Chief Executive Officer

Class A Common Stock

Former Employee

StreetEasy, Inc.

StreetEasy, Inc.

Minimum

Maximum

First Vesting Range

Second Vesting Range

First Vesting Range

Second Vesting Range

Class A Common Stock

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Increase in number of authorized shares available for awards

'

'

'

'

1,500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Substituted incentive stock options granted in connection with acquisition

'

'

'

'

'

'

'

'

'

'

'

'

25,385

15,143

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exercise price per share fixed

'

100.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

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

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Term of Award from date of grant

'

'10 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Options granted to date under various plan

'

'

'

'

'

'One-eighth of the total number of shares subject to the option will vest and become exercisable on the three-year anniversary of the grant date. An additional 1/96th of the total number of shares subject to the option 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 grant date. One-eighth of the total number of shares subject to the option will vest and become exercisable on the four-year anniversary of the grant date. An additional 1/96th of the total number of shares subject to the option 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 grant date.

'

'

'

'

'

'

'

'

'

'

'One twelfth of each restricted stock unit award will vest on each one-month anniversary of the vesting commencement date of September 20, 2013, subject to the recipientbs continued full-time employment or service to Zillow. In the event of termination of service during the first six months of employment by Zillow without cause or upon the resignation by such employee for good reason, 13,000 of the restricted stock units, less the number of restricted stock units that already vested prior to termination, will become vested units, and such employee will be entitled to receive one share of Zillowbs Class A common stock for each then outstanding unit.

'

'

'

'

'

'In general, each restricted stock unit award will vest in substantially equal installments on each one-month anniversary of the vesting commencement date over a four-year period, subject to the recipient's continued employment with or service to Zillow.

'

'Options 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

'

'

'

'

'

'

'

Expiration period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'7 years

'

'

'

'

'

'

'

Vesting percentage

'

'

'

'

'

'

'

12.50%

1.04%

'

12.50%

1.05%

'

'

'

'

8.33%

'

'

'

'

'

'

'

25.00%

'

'

'

'

'

'

'

Vesting period

'

'

'

'

'

'

'6 years

'3 years

'3 years

'7 years

'4 years

'3 years

'

'

'

'

'

'

'

'

'

'

'4 years

'

'

'

'12 months

'36 months

'

'

'

'

Number of restricted stock

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

121,123

296,004

'

'

'

'

'

'

'

'

'

230,127

340,103

'

96,792

Number of restricted stock excluded

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

97,804

'

'

26,000

'

'

54,929

'

'

'

'

3,673

'

'

121,123

Total unrecognized compensation cost

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$7,800,000

'

'

'

'

'

'

$42,300,000

'

'

'

$6,900,000

'

'

'

Unrecognized compensation cost expected recognition period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'2 years 9 months 11 days

'

'

'

'

'

'

'3 years 2 months 12 days

'

'

'

'2 years 1 month 6 days

'

'

'

Share-based compensation arrangement by share-based payment award, options, exercises in period, total intrinsic value

'

114,400,000

49,700,000

11,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Stock option of Class A common stock granted

'

'

'

'

'

500,000

'

'

'

'

'

'

'

'

30,690

'

'

'

'

'

'

'

'

'

2,009,542

'

'

'

'

'

'

'

Fair value of option granted

'

$21.26

$13.79

$4.66

'

$19

'

'

'

'

'

'

'

'

$16.29

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Expected volatility

'

'

'

'

'

51.00%

'

'

'

'

'

'

'

'

51.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Risk free interest rate

'

'

'

'

'

0.70%

'

'

'

'

'

'

'

'

0.36%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Weighted-average expected life

'

'4 years 6 months 29 days

'4 years 6 months 29 days

'4 years 6 months 29 days

'

'7 years 3 months 18 days

'

'

'

'

'

'

'

'

'3 years 6 months

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Recognized compensation cost

'

23,436,000

6,611,000

1,945,000

'

'

'

'

'

'

'

'

'

'

'

500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Vesting increment

'

'

'

'

'

'

'

'

'Monthly

'

'

'Monthly

'

'

'

'

'monthly

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Term of the option

'

'

'

'

'

'10 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'5 years 5 months 5 days

'4 years 10 months 17 days

'

'

'

'

'

'

Fair value of stock option vested

'

1,200,000

800,000

1,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total fair value of restricted stock vested

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

10,800,000

0

0

'

'

'

'

'

'

'

'

3,400,000

1,000,000

0

'

Number of restricted stock units to be vested

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

253,384

'

'

'

218,071

'

'

'

'

'

'

108,379

'

'

'

Terms of restricted stock unit award

'The former employee received one share of Zillow's Class A common stock for each outstanding restricted stock unit.

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Recognized share-based compensation expense

'

7,100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Restricted stock unit stock conversion ratio

1

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Maximum units to vest termination within 6 months

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

13,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fair value of restricted shares issued

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$2,300,000

'

'

'

'

'

$4,400,000

'

'

'

'

'

'

'

'

'

Summary_of_Stock_Option_Activi

Summary of Stock Option Activity (Detail) (Stock Options, USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Stock Options	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Shares Available for Grant, Beginning Balance	321,678	'
Shares Available for Grant, Authorized increase in plan shares	2,887,064	'
Shares Available for Grant, Granted	-1,984,157	'
Shares Available for Grant, Exercised	'	'
Shares Available for Grant, Forfeited or cancelled	288,679	'
Shares Available for Grant, Ending Balance	1,513,264	321,678
Number of Shares Subject to Existing Options, Beginning Balance	5,462,672	'
Number of Shares Subject to Existing Options, Authorized increase in plan shares	'	'
Number of Shares Subject to Existing Options, Granted	2,009,542	'
Number of Shares Subject to Existing Options, Exercised	-2,026,829	'
Number of Shares Subject to Existing Options, Forfeited or cancelled	-288,679	'
Number of Shares Subject to Existing Options, Ending Balance	5,156,706	5,462,672
Number of Shares Subject to Existing Options, Vested and exercisable	1,575,015	'
Weighted-Average Exercise Price Per Share, Beginning Balance	$14.48	'
Weighted-Average Exercise Price Per Share, Authorized increase in plan shares	'	'
Weighted-Average Exercise Price Per Share, Granted	$43.87	'
Weighted-Average Exercise Price Per Share, Exercised	$9.03	'
Weighted-Average Exercise Price Per Share, Forfeited or cancelled	$31.93	'
Weighted-Average Exercise Price Per Share, Ending Balance	$27.09	$14.48
Weighted-Average Exercise Price Per Share, Vested and exercisable	$12.02	'
Weighted-Average Remaining Contractual Life (Years)	'5 years 5 months 5 days	'4 years 10 months 17 days
Weighted-Average Remaining Contractual Life (Years), Vested and exercisable	'3 years 11 months 5 days	'
Aggregate Intrinsic Value	$283,008,505	$78,912,364
Aggregate Intrinsic Value Vested, and exercisable	$109,787,836	'

Fair_Value_of_Options_Granted_

Fair Value of Options 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, 2013	Dec. 31, 2012	Dec. 31, 2011
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'	'	'
Expected volatility, minimum	50.00%	49.00%	49.00%
Expected volatility, maximum	54.00%	52.00%	52.00%
Expected dividend yields	'	'	'
Average risk-free interest rate, minimum	0.70%	0.53%	0.79%
Average risk-free interest rate, maximum	1.27%	0.76%	1.87%
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	$21.26	$13.79	$4.66

Summary_of_Stock_Options_Outst

Summary of Stock Options Outstanding and Vested and Exercisable Stock Options (Detail) (Stock Options, USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Options Outstanding, Number Outstanding	5,156,706	5,462,672
Options Outstanding, Weighted- Average Remaining Contractual Life (Years)	'5 years 5 months 5 days	'4 years 10 months 17 days
Options Outstanding, Weighted Average Exercise Price	$27.09	$14.48
Options Vested and Exercisable, Number Exercisable	1,575,015	'
Options Vested and Exercisable, Weighted Average Exercise Price	$12.02	'
$0.08 - $3.85	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Options Outstanding, exercise price range lower limit	$0.08	'
Options Outstanding, exercise price range upper limit	$3.85	'
Options Outstanding, Number Outstanding	839,063	'
Options Outstanding, Weighted- Average Remaining Contractual Life (Years)	'3 years 2 months 27 days	'
Options Outstanding, Weighted Average Exercise Price	$3.43	'
Options Vested and Exercisable, Number Exercisable	706,969	'
Options Vested and Exercisable, Weighted Average Exercise Price	$3.47	'
$3.89 - $5.98	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Options Outstanding, exercise price range lower limit	$3.89	'
Options Outstanding, exercise price range upper limit	$5.98	'
Options Outstanding, Number Outstanding	683,918	'
Options Outstanding, Weighted- Average Remaining Contractual Life (Years)	'4 years 1 month 24 days	'
Options Outstanding, Weighted Average Exercise Price	$3.89	'
Options Vested and Exercisable, Number Exercisable	341,559	'
Options Vested and Exercisable, Weighted Average Exercise Price	$3.89	'
$6.32 - $29.50	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Options Outstanding, exercise price range lower limit	$6.32	'
Options Outstanding, exercise price range upper limit	$29.50	'
Options Outstanding, Number Outstanding	830,733	'
Options Outstanding, Weighted- Average Remaining Contractual Life (Years)	'5 years 6 months 29 days	'
Options Outstanding, Weighted Average Exercise Price	$25.38	'
Options Vested and Exercisable, Number Exercisable	173,466	'
Options Vested and Exercisable, Weighted Average Exercise Price	$20.26	'
$29.69 - $30.46	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Options Outstanding, exercise price range lower limit	$29.69	'
Options Outstanding, exercise price range upper limit	$30.46	'
Options Outstanding, Number Outstanding	527,311	'
Options Outstanding, Weighted- Average Remaining Contractual Life (Years)	'5 years 26 days	'
Options Outstanding, Weighted Average Exercise Price	$30.40	'
Options Vested and Exercisable, Number Exercisable	177,099	'
Options Vested and Exercisable, Weighted Average Exercise Price	$30.38	'
$30.60 - $36.30	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Options Outstanding, exercise price range lower limit	$30.60	'
Options Outstanding, exercise price range upper limit	$36.30	'
Options Outstanding, Number Outstanding	284,158	'
Options Outstanding, Weighted- Average Remaining Contractual Life (Years)	'5 years 1 month 24 days	'
Options Outstanding, Weighted Average Exercise Price	$32.12	'
Options Vested and Exercisable, Number Exercisable	112,581	'
Options Vested and Exercisable, Weighted Average Exercise Price	$31.41	'
36.36	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Options Outstanding, exercise price range lower limit	$36.36	'
Options Outstanding, Number Outstanding	1,393,635	'
Options Outstanding, Weighted- Average Remaining Contractual Life (Years)	'7 years 1 month 21 days	'
Options Outstanding, Weighted Average Exercise Price	$36.36	'
Options Vested and Exercisable, Number Exercisable	2,013	'
Options Vested and Exercisable, Weighted Average Exercise Price	$36.36	'
$36.72 - $89.09	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Options Outstanding, exercise price range lower limit	$36.72	'
Options Outstanding, exercise price range upper limit	$89.09	'
Options Outstanding, Number Outstanding	518,204	'
Options Outstanding, Weighted- Average Remaining Contractual Life (Years)	'6 years 2 months 27 days	'
Options Outstanding, Weighted Average Exercise Price	$57.18	'
Options Vested and Exercisable, Number Exercisable	61,328	'
Options Vested and Exercisable, Weighted Average Exercise Price	$42.52	'
$90.05 - $96.24	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Options Outstanding, exercise price range lower limit	$90.05	'
Options Outstanding, exercise price range upper limit	$96.24	'
Options Outstanding, Number Outstanding	65,328	'
Options Outstanding, Weighted- Average Remaining Contractual Life (Years)	'6 years 7 months 2 days	'
Options Outstanding, Weighted Average Exercise Price	$94.84	'
Options Vested and Exercisable, Number Exercisable	'	'
Options Vested and Exercisable, Weighted Average Exercise Price	'	'
$96.25	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Options Outstanding, exercise price range lower limit	$96.25	'
Options Outstanding, Number Outstanding	13,756	'
Options Outstanding, Weighted- Average Remaining Contractual Life (Years)	'6 years 8 months 9 days	'
Options Outstanding, Weighted Average Exercise Price	$96.25	'
Options Vested and Exercisable, Number Exercisable	'	'
Options Vested and Exercisable, Weighted Average Exercise Price	'	'
$99.09	'	'
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]	'	'
Options Outstanding, exercise price range lower limit	$99.09	'
Options Outstanding, Number Outstanding	600	'
Options Outstanding, Weighted- Average Remaining Contractual Life (Years)	'6 years 8 months 1 day	'
Options Outstanding, Weighted Average Exercise Price	$99.09	'
Options Vested and Exercisable, Number Exercisable	'	'
Options Vested and Exercisable, Weighted Average Exercise Price	'	'

Summary_of_Restricted_Stock_Aw

Summary of Restricted Stock Award Activity (Detail) (Restricted Stock, USD $)	12 Months Ended
	Dec. 31, 2013
Restricted Stock	'
Shares of Restricted Stock	'
Unvested outstanding, beginning balance	340,103
Granted	3,673
Vested	-108,379
Forfeited or cancelled	-5,270
Unvested outstanding, ending balance	230,127
Weighted-Average Grant-Date Fair Value	'
Unvested outstanding, beginning balance	$30.37
Granted	$44.66
Vested	$30.94
Forfeited or cancelled	$25.92
Unvested outstanding, ending balance	$30.43

Summary_of_Restricted_Stock_Un

Summary of Restricted Stock Units Activity (Detail) (Restricted Stock Units, USD $)	12 Months Ended
	Dec. 31, 2013
Restricted Stock Units	'
Restricted Stock Units	'
Unvested outstanding, beginning balance	296,004
Granted	97,804
Vested	-253,384
Forfeited or cancelled	-19,034
Unvested outstanding, ending balance	121,123
Weighted-Average Grant-Date Fair Value	'
Unvested outstanding, beginning balance	$38.76
Granted	$81.12
Vested	$42.53
Forfeited or cancelled	$59.26
Unvested outstanding, ending balance	$64.07

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, 2013	Dec. 31, 2012	Dec. 31, 2011
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'
Share-based compensation	$23,436	$6,611	$1,945
Cost of Revenue	'	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'
Share-based compensation	737	380	189
Sales and Marketing	'	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'
Share-based compensation	10,969	2,433	388
Technology and Development	'	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'
Share-based compensation	4,660	1,886	546
General and Administrative	'	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'
Share-based compensation	$7,070	$1,912	$822

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, 2013	Dec. 31, 2012	Dec. 31, 2011
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	2,490
Stock Options	'	'	'
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	2,490
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, 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	3,350
Stock Options	'
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	3,179
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	171

Commitments_and_Contingencies_1

Commitments and Contingencies - Additional Information (Detail) (USD $)

1 Months Ended

12 Months Ended

Nov. 30, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Apr. 30, 2013

Jul. 30, 2012

Apr. 30, 2012

Mar. 31, 2011

Sep. 30, 2013

Apr. 30, 2013

Nov. 30, 2012

Jun. 30, 2012

Apr. 30, 2012

Mar. 01, 2011

Patent

Operating Lease

Operating Lease

Operating Lease

Operating Lease

Operating Lease

Operating Lease

sqft

sqft

sqft

sqft

sqft

sqft

Property Subject to or Available for Operating Lease [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Rentable area of the premises

'

'

'

'

'

'

'

'

20,024

22,583

18,353

21,575

20,025

66,000

Rent expense

'

$4,100,000

$2,600,000

$2,100,000

'

'

'

'

'

'

'

'

'

'

Non-cancelable purchase commitments for content

'

13,613,000

'

'

'

'

'

'

'

'

'

'

'

'

Loan and security agreement to establish a line of credit

'

'

'

'

'

'

25,000,000

4,000,000

'

'

'

'

'

'

Outstanding letters of credit

'

'

'

'

$2,000,000

$1,700,000

'

$1,500,000

'

'

'

'

'

'

Expiration date of lease

'

'60 days

'

'

'

'

'

'

'

'

'

'

'

'

Number of patents-in-suit

3

'

'

'

'

'

'

'

'

'

'

'

'

'

Future_Minimum_Payments_for_Al

Future Minimum Payments for All Operating Leases (Detail) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Commitments And Contingencies Disclosure [Abstract]	'
2014	$5,353
2015	7,005
2016	7,368
2017	7,446
2018	7,494
All future years	23,505
Total future minimum lease payments	$58,171

Purchase_Commitments_for_Conte

Purchase Commitments for Content Related to Mobile Applications and Websites (Detail) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Commitments And Contingencies Disclosure [Abstract]	'
2014	$4,546
2015	4,650
2016	3,600
2017	817
2018 and all future years	'
Total future purchase commitments	$13,613

Segment_Information_and_Revenu2

Segment Information and Revenue - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2013
	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, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues:	'	'	'
Total revenue	$197,545	$116,850	$66,053
Marketplace revenue	'	'	'
Revenues:	'	'	'
Total revenue	154,208	86,670	42,190
Marketplace revenue | Real Estate Revenue	'	'	'
Revenues:	'	'	'
Total revenue	132,396	75,900	36,749
Marketplace revenue | Mortgages Revenue	'	'	'
Revenues:	'	'	'
Total revenue	21,812	10,770	5,441
Display revenue	'	'	'
Revenues:	'	'	'
Total revenue	$43,337	$30,180	$23,863

Subsequent_Events_Additional_I

Subsequent Events - Additional Information (Detail) (Subsequent Events, Seattle, Washington)	1 Months Ended
	Jan. 31, 2014
	sqft
Subsequent Events | Seattle, Washington	'
Subsequent Event [Line Items]	'
Rentable area of the premises	22,694
Start date of operating lease payments	31-Jan-17
End date of operating lease payments	30-Nov-22

Future_Minimum_Operating_Lease

Future Minimum Operating Lease Payments (Detail) (USD $)	Dec. 31, 2013	Jan. 31, 2014
In Thousands, unless otherwise specified		Seattle, Washington
		Subsequent Events
Operating Leased Assets [Line Items]	'	'
Remainder of 2014	'	'
2015	7,368	'
2016	7,446	'
2017	7,494	955
2018	'	978
All future years	23,505	4,047
Total future minimum lease payments	$58,171	$5,980