Zillow (ZG) 10-Q 6 Nov 13 2013 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2013	Oct. 30, 2013	Oct. 30, 2013
		Class A Common Stock	Class B Common Stock
Document Information [Line Items]	'	'	'
Document Type	'10-Q	'	'
Amendment Flag	'false	'	'
Document Period End Date	30-Sep-13	'	'
Document Fiscal Year Focus	'2013	'	'
Document Fiscal Period Focus	'Q3	'	'
Trading Symbol	'Z	'	'
Entity Registrant Name	'ZILLOW INC	'	'
Entity Central Index Key	'0001334814	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Filer Category	'Accelerated Filer	'	'
Entity Common Stock, Shares Outstanding	'	32,787,012	6,488,892

CONDENSED_BALANCE_SHEETS

CONDENSED BALANCE SHEETS (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$318,888	$150,040
Short-term investments	46,154	44,054
Accounts receivable, net of allowance for doubtful accounts of $1,453 and $965 at September 30, 2013 and December 31, 2012, respectively	15,712	8,655
Prepaid expenses and other current assets	5,005	2,652
Total current assets	385,759	205,401
Long-term investments	59,532	9,389
Property and equipment, net	22,528	13,634
Goodwill	93,199	54,284
Intangible assets, net	30,262	21,248
Other assets	381	279
Total assets	591,661	304,235
Current liabilities:	'	'
Accounts payable	3,987	3,158
Accrued expenses and other current liabilities	11,817	6,318
Accrued compensation and benefits	4,120	2,514
Deferred revenue	10,893	8,349
Deferred rent, current portion	198	94
Total current liabilities	31,015	20,433
Deferred rent, net of current portion	3,395	3,485
Commitments and contingencies (Note 12)	'	'
Shareholders' equity:	'	'
Additional paid-in capital	644,083	351,981
Accumulated deficit	-86,836	-71,668
Total shareholders' equity	557,251	280,317
Total liabilities and shareholders' equity	591,661	304,235
Convertible Preferred Stock	'	'
Shareholders' equity:	'	'
Preferred stock	'	'
Class A Common Stock	'	'
Shareholders' equity:	'	'
Common Stock	3	3
Class B Common Stock	'	'
Shareholders' equity:	'	'
Common Stock	$1	$1

CONDENSED_BALANCE_SHEETS_Paren

CONDENSED BALANCE SHEETS (Parenthetical) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, except Share data, unless otherwise specified
Accounts receivable, allowance for doubtful accounts	$1,453	$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	32,771,388	26,414,414
Common stock, shares outstanding	32,771,388	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	6,488,892	7,462,526
Common stock, shares outstanding	6,488,892	7,462,526

CONDENSED_STATEMENTS_OF_OPERAT

CONDENSED STATEMENTS OF OPERATIONS (USD $)	3 Months Ended				9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Income Statement [Abstract]	'		'		'		'
Revenue	$53,311		$31,915		$139,197		$82,513
Costs and expenses:	'		'		'		'
Cost of revenue (exclusive of amortization) (1)	5,116	[1]	3,623	[1]	13,540	[1]	10,237	[1]
Sales and marketing	31,195		14,118		83,913		34,586
Technology and development	12,167		6,687		33,849		17,535
General and administrative	10,357		5,192		27,568		14,869
Total costs and expenses	58,835		29,620		158,870		77,227
Income (loss) from operations	-5,524		2,295		-19,673		5,286
Other income	70		39		240		104
Income (loss) before income taxes	-5,454		2,334		-19,433		5,390
Income tax benefit	4,265		'		4,265		'
Net income (loss)	($1,189)		$2,334		($15,168)		$5,390
Net income (loss) per share - basic	($0.03)		$0.08		($0.43)		$0.19
Net income (loss) per share - diluted	($0.03)		$0.07		($0.43)		$0.17
Weighted-average shares outstanding - basic	36,667		30,040		35,011		29,115
Weighted-average shares outstanding - diluted	36,667		32,230		35,011		31,493
[1]	Amortization of website development costs and intangible assets included in technology and development

CONDENSED_STATEMENTS_OF_OPERAT1

CONDENSED STATEMENTS OF OPERATIONS (Parenthetical) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Statement [Abstract]	'	'	'	'
Amortization of website development costs and intangible assets included in technology and development	$5,092	$3,198	$13,792	$7,576

CONDENSED_STATEMENTS_OF_CASH_F

CONDENSED STATEMENTS OF CASH FLOWS (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Operating activities	'	'
Net income (loss)	($15,168)	$5,390
Adjustments to reconcile net income (loss) to net cash provided by operating activities:	'	'
Depreciation and amortization	15,811	8,702
Share-based compensation expense	18,381	4,355
Release of valuation allowance on certain deferred tax assets	-4,265	'
Loss on disposal of property and equipment	894	114
Bad debt expense	1,181	550
Deferred rent	-123	1,630
Amortization of bond premium	246	586
Changes in operating assets and liabilities:	'	'
Accounts receivable	-7,267	-3,546
Prepaid expenses and other assets	-1,427	-7
Accounts payable	723	758
Accrued expenses and other current liabilities	1,045	1,026
Deferred revenue	2,505	2,942
Net cash provided by operating activities	12,536	22,500
Investing activities	'	'
Proceeds from maturities of investments	42,000	3,600
Purchases of investments	-94,489	'
Purchases of property and equipment	-16,434	-9,652
Purchases of intangible assets	-2,629	-2,525
Acquisitions, net of cash acquired of $0 in 2013 and $2,029 in 2012	-42,615	-36,405
Net cash used in investing activities	-114,167	-44,982
Financing activities	'	'
Proceeds from exercise of Class A common stock options	16,580	6,688
Proceeds from public offering, net of offering costs	253,899	156,726
Net cash provided by financing activities	270,479	163,414
Net increase in cash and cash equivalents during period	168,848	140,932
Cash and cash equivalents at beginning of period	150,040	47,926
Cash and cash equivalents at end of period	318,888	188,858
Noncash transactions:	'	'
Capitalized share-based compensation	2,814	1,779
Write-off of fully depreciated property and equipment	$3,215	$2,986

CONDENSED_STATEMENTS_OF_CASH_F1

CONDENSED STATEMENTS OF CASH FLOWS (Parenthetical) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Statement Of Cash Flows [Abstract]	'	'
Acquisitions, cash acquired	$0	$2,029

Organization_and_Description_o

Organization and Description of Business	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
Organization and Description of Business	'
	Note 1. Organization and Description of Business
	Zillow, Inc. 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 websites, including 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	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
Summary of Significant Accounting Policies	'
	Note 2. Summary of Significant Accounting Policies
	Basis of Presentation
	The accompanying condensed financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Certain information and note disclosures normally included in the financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. Accordingly, these interim condensed financial statements should be read in conjunction with the audited financial statements and accompanying notes as of and for the year ended December 31, 2012 included in the Company’s Annual Report on Form 10-K, which was filed with the SEC on February 22, 2013. The condensed balance sheet as of December 31, 2012, included herein, was derived from the audited financial statements as of that date.
	The unaudited condensed interim financial statements have been prepared on the same basis as the annual financial statements and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, necessary to present fairly our financial position as of September 30, 2013, our results of operations for the three and nine month periods ended September 30, 2013 and 2012, and our cash flows for the nine month periods ended September 30, 2013 and 2012. The results of the three and nine month periods ended September 30, 2013 are not necessarily indicative of the results to be expected for the year ended December 31, 2013 or for any interim period or for any other future year.
	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.
	Recently Issued Accounting Standards
	In February 2013, the Financial Accounting Standards Board (“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 July 2013, the 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.

Fair_Value_Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 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 money market funds 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. Investments with maturities greater than three months but less than one year are classified as short-term investments. Investments with maturities greater than one year are classified as long-term investments. 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. Our short-term and long-term 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 short-term and long-term investments approximates their fair value.
	Of the short-term investments and long-term investments on hand as of September 30, 2013, 44% mature on or prior to September 30, 2014, and the remaining 56% mature on or prior to September 30, 2015.
	The following tables present the balances of assets measured at fair value on a recurring basis as of the dates presented (in thousands):
			September 30, 2013
			Total		Level 1		Level 2
	Cash equivalents:
	Money market funds		$	301,279	$	301,279	$	—
	Short-term investments:
	U.S government agency securities			14,823		14,823		—
	Commercial paper			3,995		—		3,995
	Corporate notes and bonds			27,335		—		27,335
	Long-term investments:
	U.S government agency securities			11,348		11,348		—
	Corporate notes and bonds			48,184		—		48,184
	Total		$	406,964	$	327,450	$	79,514
			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 or liabilities measured at fair value on a recurring basis as of September 30, 2013 or December 31, 2012.

Property_and_Equipment_Net

Property and Equipment, Net	9 Months Ended
	Sep. 30, 2013
Property Plant And Equipment [Abstract]	'
Property and Equipment, Net	'
	Note 4.	Property and Equipment, net
	The following table presents the detail of property and equipment as of the dates presented (in thousands):
			September 30,			December 31,
			2013			2012
	Website development costs		$	44,334		$	33,448
	Computer equipment			8,095			8,380
	Leasehold improvements			2,328			831
	Software			1,724			1,209
	Construction-in-progress			5,220			3,093
	Office equipment, furniture and fixtures			3,594			2,186
	Property and equipment			65,295			49,147
	Less: accumulated amortization and depreciation			(42,767	)		(35,513	)
	Property and equipment, net		$	22,528		$	13,634
	We recorded depreciation and amortization expense related to property and equipment (other than website development costs) of $0.8 million and $0.4 million, respectively, during the three months ended September 30, 2013 and 2012, and $2.0 million and $1.1 million, respectively, during the nine months ended September 30, 2013 and 2012.
	We capitalized $5.1 million and $3.5 million, respectively, in website development costs during the three months ended September 30, 2013 and 2012, and $13.2 million and $8.9 million, respectively, during the nine months ended September 30, 2013 and 2012. Amortization expense for website development costs included in technology and development expenses was $3.2 million and $1.8 million, respectively, during the three months ended September 30, 2013 and 2012, and $8.6 million and $4.6 million, respectively, during the nine months ended September 30, 2013 and 2012.
	Construction-in-progress primarily consists of website development costs that are capitalizable, but for which the associated applications had not been placed in service.

Acquisition

Acquisition	9 Months Ended
	Sep. 30, 2013
Business Combinations [Abstract]	'
Acquisition	'
	Note 5.	Acquisition
	StreetEasy, Inc.
	On August 26, 2013, Zillow, through its wholly owned subsidiary, Strawberry Acquisition, Inc., a Delaware corporation (“Merger Sub”), consummated its 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”). The acquisition aligns with our growth strategies, including focusing on consumers and deepening, strengthening, and expanding our marketplaces. With the addition of StreetEasy, Zillow expanded its 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 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 Zillow’s 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 September 30, 2013, accrued expenses and other current liabilities includes $5.6 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 $0.7 million related to an adjustment to StreetEasy’s net working capital .
	Zillow’s 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 $48.0 million, as summarized in the following table (in thousands):
	Cash payable for the outstanding stock of StreetEasy		$	42,688
	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		$	48,031
	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 the Company, 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		$	971
	Prepaid expenses and other current assets			227
	Property and equipment			1,138
	Other identifiable tangible assets			144
	Total tangible assets			2,480
	Accounts payable			(107	)
	Accrued expenses and other current liabilities			(194	)
	Accrued compensation and benefits			(224	)
	Other identifiable liabilities			(174	)
	Net deferred tax liability			(4,265	)
	Total liabilities			(4,964	)
	Net acquired liabilities			(2,484	)
	Identifiable intangible assets			11,600
	Goodwill			38,915
	Total purchase price allocation		$	48,031
	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 Zillow finalizes 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 for the three and nine months ended September 30, 2013, including legal and accounting fees and other external costs directly related to the acquisition, were not significant, 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.
	The following 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 pro forma condensed combined financial information is presented for informational purposes only. The 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 pro forma condensed combined financial information (in thousands, except per share amounts):
			Three Months Ended					Nine Months Ended
			September 30,					September 30,
			2013			2012		2013			2012
	Revenue		$	54,446		$	33,308	$	143,738		$	86,692
	Net income (loss)		$	(1,604	)	$	1,984	$	(16,836	)	$	4,340
	Net income (loss) per share - basic		$	(0.04	)	$	0.07	$	(0.48	)	$	0.15
	Net income (loss) per share - diluted		$	(0.04	)	$	0.06	$	(0.48	)	$	0.14

Goodwill

Goodwill	9 Months Ended
	Sep. 30, 2013
Goodwill And Intangible Assets Disclosure [Abstract]	'
Goodwill	'
	Note 6.	Goodwill
	The following table presents the change in goodwill from December 31, 2012 through September 30, 2013 (in thousands):
	Balance as of December 31, 2012		$	54,284
	Goodwill recorded in connection with the acquisition of StreetEasy			38,915
	Balance as of September 30, 2013		$	93,199
	The goodwill recorded in connection with the acquisition of StreetEasy is not deductible for tax purposes.

Intangible_Assets_Net

Intangible Assets, Net	9 Months Ended
	Sep. 30, 2013
Goodwill And Intangible Assets Disclosure [Abstract]	'
Intangible Assets, Net	'
	Note 7.	Intangible Assets, net
	The following tables present the detail of intangible assets subject to amortization as of the dates presented (in thousands):
			September 30, 2013
			Cost		Accumulated			Net
					Amortization
	Developed technology		$	18,835	$	(3,559	)	$	15,276
	Purchased content			11,673		(8,004	)		3,669
	Customer relationships			9,775		(1,282	)		8,493
	Trademarks			3,261		(437	)		2,824
	Total		$	43,544	$	(13,282	)	$	30,262
			December 31, 2012
			Cost		Accumulated			Net
					Amortization
	Developed technology		$	14,335	$	(1,534	)	$	12,801
	Purchased content			9,044		(6,015	)		3,029
	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 three months ended September 30, 2013 and 2012 was $1.9 million and $1.4 million, respectively. Amortization expense recorded for intangible assets for the nine months ended September 30, 2013 and 2012 was $5.2 million and $3.0 million, respectively. These amounts are included in technology and development expenses.
	Estimated future amortization expense for intangible assets, including amortization related to future commitments, as of September 30, 2013 is as follows (in thousands):
	Remainder of 2013		$	2,750
	2014			10,908
	2015			10,671
	2016			9,530
	2017			5,906
	All future years			4,915
	Total future estimated amortization expense		$	44,680

Income_Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2013
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	Note 8.	Income Taxes
	We are subject to federal and state income taxes in the United States. During the three and nine month periods ended September 30, 2013 and 2012, we did not have reportable taxable income, and we are not projecting reportable taxable income for the year ending December 31, 2013. We have provided a full valuation allowance against our net deferred tax assets as of September 30, 2013 and December 31, 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. Therefore, no tax liability or expense has been recorded in the financial statements. We have accumulated tax losses of approximately $115.7 million as of December 31, 2012, which are available to reduce future taxable income.
	We recorded an income tax benefit of $4.3 million for the three and nine month periods ended September 30, 2013 due to the use of the 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 allowance.

Shareholders_Equity

Shareholders' Equity	9 Months Ended
	Sep. 30, 2013
Equity [Abstract]	'
Shareholders' Equity	'
	Note 9.	Shareholders’ Equity
	Our board of directors has the authority to fix and determine and to amend the number of shares of any series of preferred stock that is wholly unissued or to be established and to fix and determine and to amend the designation, preferences, voting powers and limitations, and the relative, participating, optional or other rights, of any series of shares of preferred stock that is wholly unissued or to be established, subject in each case to certain approval rights of holders of our outstanding Class B common stock. There was no preferred stock issued and outstanding as of September 30, 2013 or December 31, 2012.
	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 three and nine month periods ended September 30, 2013, 600,000 shares and 973,634 shares of Class B common stock, respectively, were converted into Class A common stock at the option of the holders. During the year ended December 31, 2012, 2,065,787 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 estimated 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 estimated offering expenses payable by us. We received no proceeds from the sale of our Class A common stock by the selling shareholders.

ShareBased_Awards

Share-Based Awards	9 Months Ended
	Sep. 30, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
Share-Based Awards	'
	Note 10.	Share-Based Awards
	On July 19, 2011, our 2011 Incentive Plan (as amended and/or restated from time to time, the “2011 Plan”) became effective and 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 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 of the board of directors 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 September 30, 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 following table summarizes stock option activity for the year ended December 31, 2012 and the nine months ended September 30, 2013:
			Shares			Number			Weighted-		Weighted-		Aggregate
			Available			of Shares			Average		Average		Intrinsic
			for Grant			Subject to			Exercise		Remaining		Value
						Existing			Price Per		Contractual
						Options			Share		Life (Years)
	Outstanding at January 1, 2012			979,024			5,361,256		$	6.23		4.51	$	89,749,207
	Authorized increase in plan shares			1,068,374			—			—
	Granted			(1,884,079	)		1,884,079			30.01
	Exercised			—			(1,624,304	)		4.59
	Forfeited or cancelled			158,359			(158,359	)		21.42
	Outstanding at December 31, 2012			321,678			5,462,672			14.48		4.88		78,912,364
	Authorized increase in plan shares			2,887,064			—			—
	Granted			(1,910,112	)		1,910,112			42.08
	Exercised			—			(1,897,086	)		8.73
	Forfeited or cancelled			233,287			(233,287	)		30.34
	Outstanding at September 30, 2013			1,531,917			5,242,411			25.91		5.58		307,130,888
	Vested and exercisable at September 30, 2013						1,370,030			10.73		3.86		100,793,939
	As of September 30, 2013, the numbers above do not include 139,000 shares of restricted stock and 84,287 restricted stock units granted pursuant to our 2011 Plan. The table includes stock option awards granted in substitution of awards previously granted by companies we acquired in 2012 and 2013, which stock option awards do not reduce the number of shares available for future issuance under the 2011 Plan.
	The fair value of options granted, excluding Nonemployee Director Awards described below and certain options granted to the Company’s chief executive officer in December 2012 and January 2013, is estimated at the date of grant using the Black-Scholes-Merton option-pricing model, assuming no dividends and with the following assumptions for the periods presented:
			Three Months Ended			Nine Months Ended
			September 30,			September 30,
			2013		2012	2013		2012
	Expected volatility		54%		49%	50% - 54%		49% - 52%
	Expected dividend yields		—		—	—		—
	Risk-free interest rate		1.19% - 1.41%		0.52% - 0.54%	0.59% - 1.41%		0.52% - 0.91%
	Weighted-average expected life		4.58 years		4.58 years	4.58 years		4.58 years
	Weighted-average fair value of options granted		$38.14		$16.21	$20.23		$14.66
	In March 2013, stock options for an aggregate of 30,690 shares of our Class A common stock were granted as Nonemployee Director Awards. The fair value of options granted for the 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 three and nine month periods ended September 30, 2013, share-based compensation expense recognized in our statement of operations related to Nonemployee Director Awards was $0 and $0.5 million, respectively, and is included in general and administrative expenses.
	Restricted Stock Awards
	The following table summarizes restricted stock award activity for the year ended December 31, 2012 and the nine months ended September 30, 2013:
			Shares of			Weighted-
			Restricted Stock			Average Grant-
						Date Fair
						Value
	Unvested outstanding at January 1, 2012			75,000		$	29.69
	Granted			299,213			30.43
	Vested			(34,110	)		29.41
	Forfeited or cancelled			—			—
	Unvested outstanding at December 31, 2012			340,103			30.34
	Granted			3,673			44.66
	Vested			(22,423	)		32.14
	Forfeited or cancelled			(6,540	)		26.28
	Unvested outstanding at September 30, 2013			314,813			31.31
	The fair value of the outstanding shares of restricted stock awards will be recorded as share-based compensation expense over the vesting period. As of September 30, 2013, there was $7.8 million of total unrecognized compensation cost related to restricted stock awards.
	Restricted Stock Units
	The following table summarizes activity for restricted stock units for the year ended December 31, 2012 and the nine months ended September 30, 2013:
			Restricted Stock			Weighted-
			Units			Average Grant-
						Date Fair
						Value
	Unvested outstanding at January 1, 2012			—		$	—
	Granted			300,961			38.77
	Vested			—			—
	Forfeited or cancelled			(4,957	)		39.69
	Unvested outstanding at December 31, 2012			296,004			38.76
	Granted			30,875			83.74
	Vested			(234,002	)		39.69
	Forfeited or cancelled			(8,590	)		39.69
Unvested outstanding at September 30, 2013			84,287			55.83
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 nine months ended September 30, 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.
The fair value of restricted stock units will be recorded as share-based compensation expense over the vesting period. As of September 30, 2013, there was $4.3 million of total unrecognized compensation cost related to restricted stock units.
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):
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2013			2012			2013		2012
Cost of revenue		$	185		$	94		$	524	$	271
Sales and marketing			871			870			9,875		1,349
Technology and development			985			374			3,053		1,182
General and administrative			1,727			374			4,929		1,553
Total		$	3,768		$	1,712		$	18,381	$	4,355

Net_Income_Loss_Per_Share

Net Income (Loss) Per Share	9 Months Ended
	Sep. 30, 2013
Earnings Per Share [Abstract]	'
Net Income (Loss) Per Share	'
	Note 11.	Net Income (Loss) Per Share
	Basic net income (loss) per share is computed by dividing net income (loss) by the weighted-average number of common shares (including Class A common stock and Class B common stock) outstanding during the period. In the calculation of basic net income (loss) per share, undistributed earnings are allocated assuming all earnings during the period were distributed.
	Diluted net income (loss) per share is computed by dividing net income (loss) by the weighted-average number of common shares (including Class A common stock and Class B common stock) outstanding during the period and potentially dilutive Class A common stock equivalents, except in cases where the effect of the Class A common stock equivalent would be antidilutive. Potential Class A common stock equivalents consist of Class A common stock issuable upon exercise of stock options and Class A common stock underlying unvested restricted stock and unvested 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 per share because they had a dilutive impact (in thousands):
			Three Months Ended				Nine Months Ended
			September 30,				September 30,
			2013		2012		2013		2012
	Class A common stock issuable upon the exercise of stock options			—		2,142		—		2,324
	Class A common stock underlying unvested restricted stock awards			—		44		—		54
	Class A common stock underlying unvested restricted stock units			—		4		—		—
	Total Class A common stock equivalents			—		2,190		—		2,378
	For the periods presented, the following Class A common stock equivalents were excluded from the calculations of diluted net loss per share because their effects would have been antidilutive (in thousands):
			Three Months Ended				Nine Months Ended
			September 30,				September 30,
			2013		2012		2013		2012
	Class A common stock issuable upon the exercise of stock options			3,402		—		3,190		—
	Class A common stock underlying unvested restricted stock awards			105		—		91		—
	Class A common stock underlying unvested restricted stock units			36		—		90		—
	Total Class A common stock equivalents			3,543		—		3,371		—
	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 outstanding preferred stock have been satisfied. We have not presented net income (loss) per share under the two-class method for our Class
	A common stock and Class B common stock because it would be the same for each class due to equal dividend and liquidation rights for each class.

Commitments_and_Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2013
Commitments And Contingencies Disclosure [Abstract]	'
Commitments and Contingencies	'
	Note 12.	Commitments and Contingencies
	Lease Commitments
	We have various operating leases for office space and equipment. In March 2011, we entered into a lease 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 lease amendment for our corporate headquarters in Seattle, Washington, which will increase 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 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 September 30, 2013 are as follows (in thousands):
	Remainder of 2013		$	1,100
	2014			5,811
	2015			7,005
	2016			7,368
	2017			7,446
	All future years			31,328
	Total future minimum lease payments		$	60,058
	Rent expense for the three months ended September 30, 2013 and 2012 was $1.1 million and $0.7 million, respectively. Rent expense for the nine months ended September 30, 2013 and 2012 was $3.3 million and $1.8 million, respectively.
	Purchase Commitments
	As of September 30, 2013, we had non-cancelable purchase commitments for content related to our mobile applications and websites totaling $13.7 million. The amounts due for this content as of September 30, 2013 are as follows (in thousands):
	Remainder of 2013		$	1,021
	2014			4,157
	2015			4,291
	2016			3,435
	2017			817
	Total future purchase commitments		$	13,721
	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 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 offices, we amended our standby letter of credit to increase the amount from approximately $1.7 million to approximately $2.0 million. In November 2012, we executed a letter of credit of approximately $0.2 million in connection with the lease of our San Francisco office. The letters of credit are secured by our investments and are effective until 60 days after the expiration date of the lease.
	Legal Proceedings
	In March 2010, Smarter Agent, LLC (“Smarter Agent”) filed a complaint against us and multiple other defendants for patent infringement in the U.S. District Court for the District of Delaware. The complaint seeks, among other things, a judgment that we may 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 Office granted our petition for re-examination of the three patents-in-suit, and in an initial office action rejected all claims. In March 2011, the court granted a stay of the litigation pending the completion of the re-examination proceedings. We were granted a stay against the patent infringement complaint. 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. In addition, in March 2010, Smarter Agent filed a substantially similar complaint against HotPads, Inc. (“HotPads”), and other defendants, for patent infringement in the U.S. District Court for the District of Delaware. 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 September 30, 2013 or December 31, 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 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 may 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. We have not recorded an accrual related to this complaint as of September 30, 2013 or December 31, 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 September 30, 2013 or December 31, 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 September 30, 2013 or December 31, 2012.
	In addition to the aforementioned, 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. This forward-looking statement is based on management’s current understanding of the relevant law and facts, and it is subject to various contingencies, including the potential costs and risks associated with litigation and the actions of arbitrators, judges and juries. 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.

Segment_Information_and_Revenu

Segment Information and Revenue	9 Months Ended
	Sep. 30, 2013
Segment Reporting [Abstract]	'
Segment Information and Revenue	'
	Note 13.	Segment Information and Revenue
	We have one reportable segment. Our reportable segment has been identified based on how our chief operating decision-maker manages our business, makes operating decisions and evaluates operating performance. The chief executive officer acts as the chief operating decision-maker and reviews financial and operational information on an entity-wide basis. We have one business activity and there are no segment managers who are held accountable for operations, operating results or plans for levels or components. Accordingly, we have determined that we have a single reporting segment and operating unit structure.
	The chief executive officer reviews information about revenue categories, including marketplace revenue and display revenue. The following table presents our revenue categories during the periods presented (in thousands):
			Three Months Ended				Nine Months Ended
			September 30,				September 30,
			2013		2012		2013		2012
	Marketplace revenue:
	Real estate		$	35,136	$	21,002	$	91,882	$	52,232
	Mortgages			5,742		2,614		16,465		7,600
	Total Marketplace revenue			40,878		23,616		108,347		59,832
	Display revenue			12,433		8,299		30,850		22,681
	Total revenue		$	53,311	$	31,915	$	139,197	$	82,513

Subsequent_Events

Subsequent Events	9 Months Ended
	Sep. 30, 2013
Subsequent Events [Abstract]	'
Subsequent Events	'
	Note 14.	Subsequent Events
	In connection with our acquisition of StreetEasy, we granted restricted stock units for an aggregate 54,929 shares of our Class A common stock in October 2013 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.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
Basis of Presentation	'
	Basis of Presentation
	The accompanying condensed financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Certain information and note disclosures normally included in the financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. Accordingly, these interim condensed financial statements should be read in conjunction with the audited financial statements and accompanying notes as of and for the year ended December 31, 2012 included in the Company’s Annual Report on Form 10-K, which was filed with the SEC on February 22, 2013. The condensed balance sheet as of December 31, 2012, included herein, was derived from the audited financial statements as of that date.
	The unaudited condensed interim financial statements have been prepared on the same basis as the annual financial statements and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, necessary to present fairly our financial position as of September 30, 2013, our results of operations for the three and nine month periods ended September 30, 2013 and 2012, and our cash flows for the nine month periods ended September 30, 2013 and 2012. The results of the three and nine month periods ended September 30, 2013 are not necessarily indicative of the results to be expected for the year ended December 31, 2013 or for any interim period or for any other future year.
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.
Recently Issued Accounting Standards	'
	Recently Issued Accounting Standards
	In February 2013, the Financial Accounting Standards Board (“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 July 2013, the 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.
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.
Net Income (Loss) Per Share	'
	Basic net income (loss) per share is computed by dividing net income (loss) by the weighted-average number of common shares (including Class A common stock and Class B common stock) outstanding during the period. In the calculation of basic net income (loss) per share, undistributed earnings are allocated assuming all earnings during the period were distributed.
	Diluted net income (loss) per share is computed by dividing net income (loss) by the weighted-average number of common shares (including Class A common stock and Class B common stock) outstanding during the period and potentially dilutive Class A common stock equivalents, except in cases where the effect of the Class A common stock equivalent would be antidilutive. Potential Class A common stock equivalents consist of Class A common stock issuable upon exercise of stock options and Class A common stock underlying unvested restricted stock and unvested 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.

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 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):
		September 30, 2013
		Total		Level 1		Level 2
	Cash equivalents:
	Money market funds	$	301,279	$	301,279	$	—
	Short-term investments:
	U.S government agency securities		14,823		14,823		—
	Commercial paper		3,995		—		3,995
	Corporate notes and bonds		27,335		—		27,335
	Long-term investments:
	U.S government agency securities		11,348		11,348		—
	Corporate notes and bonds		48,184		—		48,184
	Total	$	406,964	$	327,450	$	79,514
		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

Property_and_Equipment_Net_Tab

Property and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 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):
		September 30,			December 31,
		2013			2012
	Website development costs	$	44,334		$	33,448
	Computer equipment		8,095			8,380
	Leasehold improvements		2,328			831
	Software		1,724			1,209
	Construction-in-progress		5,220			3,093
	Office equipment, furniture and fixtures		3,594			2,186
	Property and equipment		65,295			49,147
	Less: accumulated amortization and depreciation		(42,767	)		(35,513	)
	Property and equipment, net	$	22,528		$	13,634

Acquisition_Tables

Acquisition (Tables)	9 Months Ended
	Sep. 30, 2013
Business Combinations [Abstract]	'
Summary of Purchase Price	'
	The purchase price was approximately $48.0 million, as summarized in the following table (in thousands):
	Cash payable for the outstanding stock of StreetEasy	$	42,688
	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	$	48,031
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 the Company, 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	$	971
	Prepaid expenses and other current assets		227
	Property and equipment		1,138
	Other identifiable tangible assets		144
	Total tangible assets		2,480
	Accounts payable		(107	)
	Accrued expenses and other current liabilities		(194	)
	Accrued compensation and benefits		(224	)
	Other identifiable liabilities		(174	)
	Net deferred tax liability		(4,265	)
	Total liabilities		(4,964	)
	Net acquired liabilities		(2,484	)
	Identifiable intangible assets		11,600
	Goodwill		38,915
	Total purchase price allocation	$	48,031
Pro Forma Condensed Combined Financial Information	'
	The following table presents the pro forma condensed combined financial information (in thousands, except per share amounts):
		Three Months Ended					Nine Months Ended
		September 30,					September 30,
		2013			2012		2013			2012
	Revenue	$	54,446		$	33,308	$	143,738		$	86,692
	Net income (loss)	$	(1,604	)	$	1,984	$	(16,836	)	$	4,340
	Net income (loss) per share - basic	$	(0.04	)	$	0.07	$	(0.48	)	$	0.15
	Net income (loss) per share - diluted	$	(0.04	)	$	0.06	$	(0.48	)	$	0.14

Goodwill_Tables

Goodwill (Tables)	9 Months Ended
	Sep. 30, 2013
Goodwill And Intangible Assets Disclosure [Abstract]	'
Change in Goodwill	'
	The following table presents the change in goodwill from December 31, 2012 through September 30, 2013 (in thousands):
	Balance as of December 31, 2012	$	54,284
	Goodwill recorded in connection with the acquisition of StreetEasy		38,915
	Balance as of September 30, 2013	$	93,199

Intangible_Assets_Net_Tables

Intangible Assets, Net (Tables)	9 Months Ended
	Sep. 30, 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):
		September 30, 2013
		Cost		Accumulated			Net
				Amortization
	Developed technology	$	18,835	$	(3,559	)	$	15,276
	Purchased content		11,673		(8,004	)		3,669
	Customer relationships		9,775		(1,282	)		8,493
	Trademarks		3,261		(437	)		2,824
	Total	$	43,544	$	(13,282	)	$	30,262
		December 31, 2012
		Cost		Accumulated			Net
				Amortization
	Developed technology	$	14,335	$	(1,534	)	$	12,801
	Purchased content		9,044		(6,015	)		3,029
	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 September 30, 2013 is as follows (in thousands):
	Remainder of 2013	$	2,750
	2014		10,908
	2015		10,671
	2016		9,530
	2017		5,906
	All future years		4,915
	Total future estimated amortization expense	$	44,680

ShareBased_Awards_Tables

Share-Based Awards (Tables)	9 Months Ended
	Sep. 30, 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, 2012 and the nine months ended September 30, 2013:
		Shares			Number			Weighted-		Weighted-		Aggregate
		Available			of Shares			Average		Average		Intrinsic
		for Grant			Subject to			Exercise		Remaining		Value
					Existing			Price Per		Contractual
					Options			Share		Life (Years)
	Outstanding at January 1, 2012		979,024			5,361,256		$	6.23		4.51	$	89,749,207
	Authorized increase in plan shares		1,068,374			—			—
	Granted		(1,884,079	)		1,884,079			30.01
	Exercised		—			(1,624,304	)		4.59
	Forfeited or cancelled		158,359			(158,359	)		21.42
	Outstanding at December 31, 2012		321,678			5,462,672			14.48		4.88		78,912,364
	Authorized increase in plan shares		2,887,064			—			—
	Granted		(1,910,112	)		1,910,112			42.08
	Exercised		—			(1,897,086	)		8.73
	Forfeited or cancelled		233,287			(233,287	)		30.34
	Outstanding at September 30, 2013		1,531,917			5,242,411			25.91		5.58		307,130,888
	Vested and exercisable at September 30, 2013					1,370,030			10.73		3.86		100,793,939
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 described below and certain options granted to the Company’s chief executive officer in December 2012 and January 2013, is estimated at the date of grant using the Black-Scholes-Merton option-pricing model, assuming no dividends and with the following assumptions for the periods presented:
		Three Months Ended			Nine Months Ended
		September 30,			September 30,
		2013		2012	2013		2012
	Expected volatility	54%		49%	50% - 54%		49% - 52%
	Expected dividend yields	—		—	—		—
	Risk-free interest rate	1.19% - 1.41%		0.52% - 0.54%	0.59% - 1.41%		0.52% - 0.91%
	Weighted-average expected life	4.58 years		4.58 years	4.58 years		4.58 years
	Weighted-average fair value of options granted	$38.14		$16.21	$20.23		$14.66
Summary of Restricted Stock Award Activity	'
	The following table summarizes restricted stock award activity for the year ended December 31, 2012 and the nine months ended September 30, 2013:
		Shares of			Weighted-
		Restricted			Average Grant-
		Stock			Date Fair
					Value
	Unvested outstanding at January 1, 2012		75,000		$	29.69
	Granted		299,213			30.43
	Vested		(34,110	)		29.41
	Forfeited or cancelled		—			—
	Unvested outstanding at December 31, 2012		340,103			30.34
	Granted		3,673			44.66
	Vested		(22,423	)		32.14
	Forfeited or cancelled		(6,540	)		26.28
	Unvested outstanding at September 30, 2013		314,813			31.31
Summary of Restricted Stock Units Activity	'
	The following table summarizes activity for restricted stock units for the year ended December 31, 2012 and the nine months ended September 30, 2013:
		Restricted Stock			Weighted-
		Units			Average Grant-
					Date Fair
					Value
	Unvested outstanding at January 1, 2012		—		$	—
	Granted		300,961			38.77
	Vested		—			—
	Forfeited or cancelled		(4,957	)		39.69
	Unvested outstanding at December 31, 2012		296,004			38.76
	Granted		30,875			83.74
	Vested		(234,002	)		39.69
	Forfeited or cancelled		(8,590	)		39.69
	Unvested outstanding at September 30, 2013		84,287			55.83
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):
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2013			2012			2013		2012
	Cost of revenue	$	185		$	94		$	524	$	271
	Sales and marketing		871			870			9,875		1,349
	Technology and development		985			374			3,053		1,182
	General and administrative		1,727			374			4,929		1,553
	Total	$	3,768		$	1,712		$	18,381	$	4,355

Net_Income_Loss_Per_Share_Tabl

Net Income (Loss) Per Share (Tables)	9 Months Ended
	Sep. 30, 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 per share because they had a dilutive impact (in thousands):
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
		2013		2012		2013		2012
	Class A common stock issuable upon the exercise of stock options		—		2,142		—		2,324
	Class A common stock underlying unvested restricted stock awards		—		44		—		54
	Class A common stock underlying unvested restricted stock units		—		4		—		—
	Total Class A common stock equivalents		—		2,190		—		2,378
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 effects would have been antidilutive (in thousands):
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
		2013		2012		2013		2012
	Class A common stock issuable upon the exercise of stock options		3,402		—		3,190		—
	Class A common stock underlying unvested restricted stock awards		105		—		91		—
	Class A common stock underlying unvested restricted stock units		36		—		90		—
	Total Class A common stock equivalents		3,543		—		3,371		—

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2013
Commitments And Contingencies Disclosure [Abstract]	'
Future Minimum Payments for All Operating Leases	'
	Future minimum payments for all operating leases as of September 30, 2013 are as follows (in thousands):
	Remainder of 2013	$	1,100
	2014		5,811
	2015		7,005
	2016		7,368
	2017		7,446
	All future years		31,328
	Total future minimum lease payments	$	60,058
Purchase Commitments for Content Related to Mobile Applications and Websites	'
	The amounts due for this content as of September 30, 2013 are as follows (in thousands):
	Remainder of 2013	$	1,021
	2014		4,157
	2015		4,291
	2016		3,435
	2017		817
	Total future purchase commitments	$	13,721

Segment_Information_and_Revenu1

Segment Information and Revenue (Tables)	9 Months Ended
	Sep. 30, 2013
Segment Reporting [Abstract]	'
Revenue Categories	'
	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):
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
		2013		2012		2013		2012
	Marketplace revenue:
	Real estate	$	35,136	$	21,002	$	91,882	$	52,232
	Mortgages		5,742		2,614		16,465		7,600
	Total Marketplace revenue		40,878		23,616		108,347		59,832
	Display revenue		12,433		8,299		30,850		22,681
	Total revenue	$	53,311	$	31,915	$	139,197	$	82,513

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 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 classification	'Investments with maturities greater than three months but less than one year are classified as short-term investments. Investments with maturities greater than one year are classified as long-term investments.	'	'	'	'
Investment Maturity, Percentage	'	0.44%	0.56%	'	'
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 $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total	$406,964	$196,689
Money Market Funds	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Cash equivalents	301,279	143,246
U.S government agency securities	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Short-term investments	14,823	26,085
Long-term investments	11,348	7,079
Commercial Paper	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Short-term investments	3,995	16,965
Corporate Notes and Bonds	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Short-term investments	27,335	1,004
Long-term investments	48,184	2,310
Fair Value, Inputs, Level 1	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Total	327,450	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	301,279	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]	'	'
Short-term investments	14,823	26,085
Long-term investments	11,348	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	79,514	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]	'	'
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	3,995	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	27,335	1,004
Long-term investments	$48,184	$2,310

Detail_of_Property_and_Equipme

Detail of Property and Equipment (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	$65,295	$49,147
Less: accumulated amortization and depreciation	-42,767	-35,513
Property and equipment, net	22,528	13,634
Website Development Costs	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	44,334	33,448
Computer Equipment	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	8,095	8,380
Leasehold Improvements	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	2,328	831
Software and Software Development Costs [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	1,724	1,209
Construction in Progress	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	5,220	3,093
Office Equipment, Furniture and Fixtures	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	$3,594	$2,186

Property_and_Equipment_Net_Add

Property and Equipment, Net - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Property, Plant and Equipment [Line Items]	'	'	'	'
Depreciation and amortization expense related to property and equipment other than website development costs	$800,000	$400,000	$2,000,000	$1,100,000
Capitalization of website development costs	5,100,000	3,500,000	13,200,000	8,900,000
Amortization expense for website development costs included in technology and development expenses	5,092,000	3,198,000	13,792,000	7,576,000
Technology and Development	'	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'	'
Amortization expense for website development costs included in technology and development expenses	1,900,000	1,400,000	5,200,000	3,000,000
Technology and Development | Website Development Costs	'	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'	'
Amortization expense for website development costs included in technology and development expenses	$3,200,000	$1,800,000	$8,600,000	$4,600,000

Acquisition_Additional_Informa

Acquisition - Additional Information (Detail) (USD $)	Sep. 30, 2013	Sep. 30, 2013	Aug. 26, 2013
		Maximum	StreetEasy, Inc.
Business Acquisition [Line Items]	'	'	'
Cash paid for outstanding stock	'	'	$42,688,000
Consideration deposited in escrow	'	'	5,000,000
Accrued expenses and other current liabilities in connection with acquisition	5,600,000	'	'
Prepaid expenses and other current assets	700,000	'	227,000
Total purchase price	'	'	$48,031,000
Estimates and assumptions related to the purchase price allocation	'	'1 year	'

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	$42,688
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	$48,031

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 $)	Sep. 30, 2013	Dec. 31, 2012	Aug. 26, 2013
In Thousands, unless otherwise specified			StreetEasy, Inc.
Business Acquisition [Line Items]	'	'	'
Accounts receivable	'	'	$971
Prepaid expenses and other current assets	700	'	227
Property and equipment	'	'	1,138
Other identifiable tangible assets	'	'	144
Total tangible assets	'	'	2,480
Accounts payable	'	'	-107
Accrued expenses and other current liabilities	'	'	-194
Accrued compensation and benefits	'	'	-224
Other identifiable liabilities	'	'	-174
Net deferred tax liability	'	'	-4,265
Total liabilities	'	'	-4,964
Net acquired liabilities	'	'	-2,484
Identifiable intangible assets	'	'	11,600
Goodwill	93,199	54,284	38,915
Total purchase price	'	'	$48,031

Pro_Forma_Condensed_Combined_F

Pro Forma Condensed Combined Financial Information (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Business Combinations [Abstract]	'	'	'	'
Revenue	$54,446	$33,308	$143,738	$86,692
Net income (loss)	($1,604)	$1,984	($16,836)	$4,340
Net income (loss) per share-basic	($0.04)	$0.07	($0.48)	$0.15
Net income (loss) per share-diluted	($0.04)	$0.06	($0.48)	$0.14

Change_in_Goodwill_Detail

Change in Goodwill (Detail) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013
Goodwill And Intangible Assets Disclosure [Abstract]	'
Balance as of December 31, 2012	$54,284
Goodwill recorded in connection with the acquisition of StreetEasy	38,915
Balance as of September 30, 2013	$93,199

Intangible_Assets_Detail

Intangible Assets (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Finite-Lived Intangible Assets [Line Items]	'	'
Cost	$43,544	$29,315
Accumulated Amortization	-13,282	-8,067
Net	30,262	21,248
Developed Technology	'	'
Finite-Lived Intangible Assets [Line Items]	'	'
Cost	18,835	14,335
Accumulated Amortization	-3,559	-1,534
Net	15,276	12,801
Purchased Content	'	'
Finite-Lived Intangible Assets [Line Items]	'	'
Cost	11,673	9,044
Accumulated Amortization	-8,004	-6,015
Net	3,669	3,029
Customer Relationships	'	'
Finite-Lived Intangible Assets [Line Items]	'	'
Cost	9,775	4,875
Accumulated Amortization	-1,282	-387
Net	8,493	4,488
Trademarks	'	'
Finite-Lived Intangible Assets [Line Items]	'	'
Cost	3,261	1,061
Accumulated Amortization	-437	-131
Net	$2,824	$930

Intangible_Assets_Net_Addition

Intangible Assets, Net - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Finite-Lived Intangible Assets [Line Items]	'	'	'	'
Amortization of website development costs and intangible assets	$5,092	$3,198	$13,792	$7,576
Technology and Development	'	'	'	'
Finite-Lived Intangible Assets [Line Items]	'	'	'	'
Amortization of website development costs and intangible assets	$1,900	$1,400	$5,200	$3,000

Estimated_Future_Amortization_

Estimated Future Amortization Expense for Intangible Assets (Detail) (USD $)	Sep. 30, 2013
In Thousands, unless otherwise specified
Goodwill And Intangible Assets Disclosure [Abstract]	'
Remainder of 2013	$2,750
2014	10,908
2015	10,671
2016	9,530
2017	5,906
All future years	4,915
Total future estimated amortization expense	$44,680

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]	'	'	'
Minimum estimated percentage of deferred tax unrealized	'	50.00%	'
Net operating loss carryforwards	'	'	$115,700,000
Income tax benefit	$4,265,000	$4,265,000	'

Shareholders_Equity_Additional

Shareholders' Equity - Additional Information (Detail) (USD $)	1 Months Ended		3 Months Ended	9 Months Ended	12 Months Ended
In Millions, except Share data, unless otherwise specified	Aug. 31, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2013	Dec. 31, 2012
Class of Stock [Line Items]	'	'	'	'	'
Number of common stock converted	'	'	600,000	973,634	2,065,787
Net proceeds from issuance of common stock	$253.90	$156.70	'	'	'
Class A Common Stock	'	'	'	'	'
Class of Stock [Line Items]	'	'	'	'	'
Common stock holders voting right	'	'	'	1	'
Conversion of common stock conversion ratio	'	'	'	'	1
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

ShareBased_Awards_Additional_I

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

1 Months Ended

3 Months Ended

9 Months Ended

9 Months Ended

12 Months Ended

9 Months Ended

1 Months Ended

9 Months Ended

12 Months Ended

1 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

12 Months Ended

Apr. 30, 2013

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

31-May-13

Sep. 30, 2013

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Apr. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Mar. 31, 2013

Sep. 30, 2013

Sep. 30, 2013

Dec. 31, 2012

HotPads, Inc.

Restricted Stock

Restricted Stock

Restricted Stock

Restricted Stock Units

Restricted Stock Units

Restricted Stock Units

Restricted Stock Units

Restricted Stock Units

Restricted Stock Units

Non Employee Director Rewards

Non Employee Director Rewards

Non Employee Director Rewards

Stock Options

Stock Options

2011 Plan

Class A Common Stock

Former Employee

2011 Plan

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

'

'

'

'

'

'

15,143

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exercise price per share fixed

'

'

'

100.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Share based compensation arrangement by share based payment, award minimum exercisable period

'

'3 months

'

'3 months

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Share based compensation arrangement by share based payment, award maximum exercisable period

'

'12 months

'

'12 months

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Term of Award from date of grant

'

'

'

'10 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of Vested Restricted Stock Unit

'

'

'

25.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Options granted to date under various plan

'

'

'

'

'

'

'

'

'

'

'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.

'

'

'

'

'

'

'

'

'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,

'

Number of restricted stock excluded

'

'

'

'

'

'

'

3,673

299,213

139,000

'

30,875

300,961

26,000

'

84,287

'

'

'

'

'

Stock option of Class A common stock granted

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

30,690

'

1,910,112

1,884,079

Fair value of options granted

'

$38.14

$16.21

$20.23

$14.66

'

'

'

'

'

'

'

'

'

'

'

'

$16.29

'

'

'

Expected volatility

'

54.00%

49.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

51.00%

'

'

'

Risk-free interest rate

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0.36%

'

'

'

Weighted-average expected life

'

'4 years 6 months 29 days

'4 years 6 months 29 days

'4 years 6 months 29 days

'4 years 6 months 29 days

'

'

'

'

'

'

'

'

'

'

'

'

'3 years 6 months

'

'

'

Recognized compensation cost

'

$3,768,000

$1,712,000

$18,381,000

$4,355,000

'

'

'

'

'

'

'

'

'

'

'

$0

'

$500,000

'

'

Total unrecognized compensation cost

'

'

'

'

'

'

'

7,800,000

'

'

4,300,000

4,300,000

'

'

'

'

'

'

'

'

'

Number of restricted stock units to be vested

'

'

'

'

'

'

'

22,423

34,110

'

'

234,002

'

'

218,071

'

'

'

'

'

'

Terms of restricted stock unit award

'The former employee is entitled to receive 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

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fair value of restricted shares issued

'

'

'

'

'

'

'

'

'

'

$2,300,000

'

'

'

'

'

'

'

'

'

'

Summary_of_Stock_Option_Activi

Summary of Stock Option Activity (Detail) (Stock Options, USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2011
Stock Options	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Shares Available for Grant, Beginning Balance	321,678	979,024	'
Shares Available for Grant, Authorized increase in plan shares	2,887,064	1,068,374	'
Shares Available for Grant, Granted	-1,910,112	-1,884,079	'
Shares Available for Grant, Exercised	'	'	'
Shares Available for Grant, Forfeited or cancelled	233,287	158,359	'
Shares Available for Grant, Ending Balance	1,531,917	321,678	979,024
Number of Shares Subject to Existing Options, Beginning Balance	5,462,672	5,361,256	'
Number of Shares Subject to Existing Options, Authorized increase in plan shares	'	'	'
Number of Shares Subject to Existing Options, Granted	1,910,112	1,884,079	'
Number of Shares Subject to Existing Options, Exercised	-1,897,086	-1,624,304	'
Number of Shares Subject to Existing Options, Forfeited or cancelled	-233,287	-158,359	'
Number of Shares Subject to Existing Options, Ending Balance	5,242,411	5,462,672	5,361,256
Weighted-Average Exercise Price Per Share, Beginning Balance	$14.48	$6.23	'
Number of Shares Subject to Existing Options, Vested and exercisable	1,370,030	'	'
Weighted-Average Exercise Price Per Share, Authorized increase in plan shares	'	'	'
Weighted-Average Exercise Price Per Share, Granted	$42.08	$30.01	'
Weighted-Average Exercise Price Per Share, Exercised	$8.73	$4.59	'
Weighted-Average Exercise Price Per Share, Forfeited or cancelled	$30.34	$21.42	'
Weighted-Average Exercise Price Per Share, Ending Balance	$25.91	$14.48	$6.23
Weighted-Average Exercise Price Per Share, Vested and exercisable	$10.73	'	'
Weighted-Average Remaining Contractual Life (Years)	'5 years 6 months 29 days	'4 years 10 months 17 days	'4 years 6 months 4 days
Weighted-Average Remaining Contractual Life (Years), Vested and exercisable	'3 years 10 months 10 days	'	'
Aggregate Intrinsic Value	$307,130,888	$78,912,364	$89,749,207
Aggregate Intrinsic Value, Vested and exercisable	$100,793,939	'	'

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 $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'	'	'	'
Expected volatility	54.00%	49.00%	'	'
Expected volatility, minimum	'	'	50.00%	49.00%
Expected volatility, maximum	'	'	54.00%	52.00%
Expected dividend yields	'	'	'	'
Risk-free interest rate, minimum	1.19%	0.52%	0.59%	0.52%
Risk-free interest rate, maximum	1.41%	0.54%	1.41%	0.91%
Weighted-average expected life	'4 years 6 months 29 days	'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	$38.14	$16.21	$20.23	$14.66

Summary_of_Restricted_Stock_Aw

Summary of Restricted Stock Award Activity (Detail) (Restricted Stock, USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Restricted Stock	'	'
Shares of Restricted Stock	'	'
Unvested outstanding, beginning balance	340,103	75,000
Granted	3,673	299,213
Vested	-22,423	-34,110
Forfeited or cancelled	-6,540	'
Unvested outstanding, ending balance	314,813	340,103
Weighted-Average Grant-Date Fair Value	'	'
Unvested outstanding, beginning balance	$30.34	$29.69
Granted	$44.66	$30.43
Vested	$32.14	$29.41
Forfeited or cancelled	$26.28	'
Unvested outstanding, ending balance	$31.31	$30.34

Summary_of_Restricted_Stock_Un

Summary of Restricted Stock Units Activity (Detail) (Restricted Stock Units, USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Restricted Stock Units	'	'
Restricted Stock Units	'	'
Unvested outstanding, beginning balance	296,004	0
Granted	30,875	300,961
Vested	-234,002	'
Forfeited or cancelled	-8,590	-4,957
Unvested outstanding, ending balance	84,287	296,004
Weighted-Average Grant-Date Fair Value	'	'
Unvested outstanding, beginning balance	$38.76	$0
Granted	$83.74	$38.77
Vested	$39.69	'
Forfeited or cancelled	$39.69	$39.69
Unvested outstanding, ending balance	$55.83	$38.76

Effects_of_Share_Based_Compens

Effects of Share Based Compensation in Statements of Operations (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'	'
Share-based compensation	$3,768	$1,712	$18,381	$4,355
Cost of Revenue	'	'	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'	'
Share-based compensation	185	94	524	271
Sales and Marketing	'	'	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'	'
Share-based compensation	871	870	9,875	1,349
Technology and Development	'	'	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'	'
Share-based compensation	985	374	3,053	1,182
General and Administrative	'	'	'	'
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]	'	'	'	'
Share-based compensation	$1,727	$374	$4,929	$1,553

Dilutive_Securities_Included_i

Dilutive Securities Included in Computation of Earnings Per Share (Detail) (Class A Common Stock)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]	'	'	'	'
Class A common stock equivalents included in the computation of diluted net income per share	'	2,190	'	2,378
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	'	2,142	'	2,324
Restricted Stock	'	'	'	'
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	'	44	'	54
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	'	4	'	'

Antidilutive_Securities_Exclud

Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) (Class A Common Stock)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
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	3,543	'	3,371	'
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	3,402	'	3,190	'
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	105	'	91	'
Restricted Stock Units	'	'	'	'
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	36	'	90	'

Commitments_and_Contingencies_1

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

1 Months Ended

3 Months Ended

9 Months Ended

Nov. 30, 2010

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Apr. 30, 2013

Nov. 30, 2012

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

'

'

$1,100,000

$700,000

$3,300,000

$1,800,000

'

'

'

'

'

'

'

'

'

'

'

Non-cancelable purchase commitments for content

'

'

13,721,000

'

13,721,000

'

'

'

'

'

'

'

'

'

'

'

'

Loan and security agreement to establish a line of credit

'

'

'

'

'

'

'

'

'

25,000,000

4,000,000

'

'

'

'

'

'

Outstanding letters of credit

'

'

'

'

'

'

$2,000,000

$200,000

$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 $)	Sep. 30, 2013
In Thousands, unless otherwise specified
Commitments And Contingencies Disclosure [Abstract]	'
Remainder of 2013	$1,100
2014	5,811
2015	7,005
2016	7,368
2017	7,446
All future years	31,328
Total future minimum lease payments	$60,058

Purchase_Commitments_for_Conte

Purchase Commitments for Content Related to Mobile Applications and Websites (Detail) (USD $)	Sep. 30, 2013
In Thousands, unless otherwise specified
Commitments And Contingencies Disclosure [Abstract]	'
Remainder of 2013	$1,021
2014	4,157
2015	4,291
2016	3,435
2017	817
Total future purchase commitments	$13,721

Segment_Information_and_Revenu2

Segment Information and Revenue - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2013
	Segment
Segment Reporting [Abstract]	'
Number of reportable segment	1

Revenue_Categories_Detail

Revenue Categories (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues:	'	'	'	'
Total revenue	$53,311	$31,915	$139,197	$82,513
Operating Segments | Marketplace revenue	'	'	'	'
Revenues:	'	'	'	'
Total revenue	40,878	23,616	108,347	59,832
Operating Segments | Marketplace revenue | Real Estate Revenue	'	'	'	'
Revenues:	'	'	'	'
Total revenue	35,136	21,002	91,882	52,232
Operating Segments | Marketplace revenue | Mortgages Revenue	'	'	'	'
Revenues:	'	'	'	'
Total revenue	5,742	2,614	16,465	7,600
Operating Segments | Display revenue	'	'	'	'
Revenues:	'	'	'	'
Total revenue	$12,433	$8,299	$30,850	$22,681

Subsequent_Events_Additional_I

Subsequent Events - Additional Information (Detail) (Restricted Stock Units, USD $)	1 Months Ended	9 Months Ended	12 Months Ended	1 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2013	Dec. 31, 2012	Oct. 31, 2013
				Subsequent Events
				StreetEasy, Inc.
Subsequent Event [Line Items]	'	'	'	'
Restricted stock units of Class A common stock granted	'	30,875	300,961	54,929
Fair value of restricted shares issued	$2.30	'	'	$4.40
Restricted stock unit, award vesting period	'	'	'	'4 years