Zillow (Z) 10-K 21 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 15, 2019	Jun. 30, 2018
Document Information [Line Items]
Document Type	10-K
Amendment Flag	false
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Trading Symbol	ZG
Entity Registrant Name	ZILLOW GROUP, INC.
Entity Central Index Key	1,617,640
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 10,442,769,057
Class A Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		58,111,740
Class B Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		6,217,447
Class C Capital Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		140,268,416

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 651,058	$ 352,095
Short-term investments	903,867	410,444
Accounts receivable, net of allowance for doubtful accounts of $4,838 and $5,341 at December 31, 2018 and 2017, respectively	66,083	54,396
Inventory	162,829	0
Mortgage loans held for sale	35,409	0
Prepaid expenses and other current assets	61,067	24,590
Restricted cash	12,385	0
Total current assets	1,892,698	841,525
Contract cost assets	45,819	0
Property and equipment, net	135,172	112,271
Goodwill	1,984,907	1,931,076
Intangible assets, net	215,904	319,711
Other assets	16,616	25,934
Total assets	4,291,116	3,230,517
Current liabilities:
Accounts payable	7,471	3,587
Accrued expenses and other current liabilities	63,101	61,373
Accrued compensation and benefits	31,388	19,109
Revolving credit facility	116,700	0
Warehouse lines of credit	33,018	0
Deferred revenue	34,080	31,918
Deferred rent, current portion	1,740	2,400
Total current liabilities	287,498	118,387
Deferred rent, net of current portion	19,945	21,330
Long-term debt	699,020	385,416
Deferred tax liabilities and other long-term liabilities	17,474	44,561
Total liabilities	1,023,937	569,694
Commitments and contingencies (Note 19)
Shareholders’ equity:
Preferred stock, $0.0001 par value; 30,000,000 shares authorized; no shares issued and outstanding	0	0
Additional paid-in capital	3,939,842	3,254,146
Accumulated other comprehensive loss	(905)	(1,100)
Accumulated deficit	(671,779)	(592,243)
Total shareholders’ equity	3,267,179	2,660,823
Total liabilities and shareholders’ equity	4,291,116	3,230,517
Class A Common Stock
Shareholders’ equity:
Common stock	6	6
Class B Common Stock
Shareholders’ equity:
Common stock	1	1
Class C Capital Stock
Shareholders’ equity:
Common stock	$ 14	$ 13

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts receivable, allowance for doubtful accounts	$ 4,838	$ 5,341
Preferred stock, par value (usd per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	30,000,000	30,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Class A Common Stock
Common stock, par value (usd per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	1,245,000,000	1,245,000,000
Common stock, shares issued (in shares)	58,051,448	56,629,103
Common stock, shares outstanding (in shares)	58,051,448	56,629,103
Class B Common Stock
Common stock, par value (usd per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	15,000,000	15,000,000
Common stock, shares issued (in shares)	6,217,447	6,217,447
Common stock, shares outstanding (in shares)	6,217,447	6,217,447
Class C Capital Stock
Common stock, par value (usd per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	600,000,000	600,000,000
Common stock, shares issued (in shares)	139,635,370	127,268,598
Common stock, shares outstanding (in shares)	139,635,370	127,268,598

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue:
Total revenue		$ 1,333,554	$ 1,076,794	$ 846,589
Cost of revenue (exclusive of amortization):
Cost of revenue (exclusive of amortization)	[1]	153,590	85,203	69,262
Sales and marketing		552,621	448,201	382,419
Technology and development		410,818	319,985	255,583
General and administrative		262,153	210,816	332,007
Impairment costs		79,000	174,000	0
Acquisition-related costs		2,332	463	1,423
Integration costs		2,015	0	0
Gain on divestiture of business		0	0	(1,251)
Total costs and expenses		1,462,529	1,238,668	1,039,443
Loss from operations		(128,975)	(161,874)	(192,854)
Loss on debt extinguishment		0	0	(22,757)
Other income		19,270	5,385	2,711
Interest expense		(41,255)	(27,517)	(7,408)
Loss before income taxes		(150,960)	(184,006)	(220,308)
Income tax benefit (expense)		31,102	89,586	(130)
Net loss		$ (119,858)	$ (94,420)	$ (220,438)
Net loss per share-basic and diluted (usd per share)		$ (0.61)	$ (0.51)	$ (1.22)
Weighted-average shares outstanding-basic and diluted (in shares)		197,944	186,453	180,149
Amortization of website development costs and intangible assets included in technology and development		$ 79,309	$ 94,349	$ 87,060
IMT
Revenue:
Total revenue		1,281,189	1,076,794	846,589
Cost of revenue (exclusive of amortization):
Cost of revenue (exclusive of amortization)	[1]	104,330	85,203	69,262
Homes
Revenue:
Total revenue		52,365	0	0
Cost of revenue (exclusive of amortization):
Cost of revenue (exclusive of amortization)	[1]	$ 49,260	$ 0	$ 0
[1]	Amortization of website development costs and intangible assets included in technology and development was $79,309, $94,349 and $87,060 for the periods ended December 31, 2018, 2017 and 2016, respectively.

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net loss	$ (119,858)	$ (94,420)	$ (220,438)
Other comprehensive income (loss):
Unrealized gains (losses) on investments	144	(858)	229
Currency translation adjustments	51	0	0
Total other comprehensive income (loss)	195	(858)	229
Comprehensive loss	$ (119,663)	$ (95,278)	$ (220,209)

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Class A Common Stock, Class B Common Stock and Class C Capital Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss
Beginning Balance at Dec. 31, 2015	$ 2,679,053	$ 18	$ 2,956,111	$ (276,605)	$ (471)
Beginning Balance (in shares) at Dec. 31, 2015		178,474,917
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common and capital stock upon exercise of stock options	31,211	$ 0	31,211
Issuance of common and capital stock upon exercise of stock options (in shares)		2,518,172
Vesting of restricted stock units	0		0
Vesting of restricted stock units (in shares)		1,487,263
Shares and value of restricted stock units withheld for tax liability	(616)		(616)
Shares and value of restricted stock units withheld for tax liability (in shares)		(21,634)
Share-based compensation expense	116,979		116,979
Portion of repurchase price recorded in additional paid-in capital in connection with partial repurchase/conversion of 2020	(127,615)		(127,615)
Equity component of issuance of 2021 Notes, net of issuance costs of $2,494	91,400		91,400
Premiums paid for Capped Call Confirmations	(36,616)		(36,616)
Net loss	(220,438)		0	(220,438)
Other comprehensive income (loss)	229			0	229
Ending Balance at Dec. 31, 2016	2,533,587	$ 18	3,030,854	(497,043)	(242)
Ending Balance (in shares) at Dec. 31, 2016		182,458,718
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common and capital stock upon exercise of stock options	98,072	$ 2	98,070
Issuance of common and capital stock upon exercise of stock options (in shares)		6,202,421
Vesting of restricted stock units	0		0
Vesting of restricted stock units (in shares)		1,463,825
Shares and value of restricted stock units withheld for tax liability	(365)		(365)
Shares and value of restricted stock units withheld for tax liability (in shares)		(9,816)
Share-based compensation expense	124,807		124,807
Net loss	(94,420)		0	(94,420)
Other comprehensive income (loss)	(858)				(858)
Ending Balance at Dec. 31, 2017	2,660,823	$ 20	3,254,146	(592,243)	(1,100)
Ending Balance (in shares) at Dec. 31, 2017		190,115,148
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common and capital stock upon exercise of stock options	120,074		120,074
Issuance of common and capital stock upon exercise of stock options (in shares)		5,472,728
Vesting of restricted stock units	0
Vesting of restricted stock units (in shares)		1,740,134
Shares and value of restricted stock units withheld for tax liability	(70)		(70)
Shares and value of restricted stock units withheld for tax liability (in shares)		(1,489)
Share-based compensation expense	157,674		157,674
Portion of conversion recorded in additional paid-in-capital in connection with partial conversion of 2020 Notes	500		500
Portion of conversion recorded in additional paid-in-capital in connection with partial conversion of 2020 Notes (in shares)		20,727
Issuance of Class C capital stock in connection with equity offering, net of issuance costs	360,346	$ 1	360,345
Issuance of Class C capital stock in connection with equity offering, net of issuance costs (in shares)		6,557,017
Equity component of issuance of 2021 Notes, net of issuance costs of $2,494	76,587		76,587
Premiums paid for Capped Call Confirmations	(29,414)		(29,414)
Net loss	(119,858)			(119,858)
Other comprehensive income (loss)	195				195
Ending Balance at Dec. 31, 2018	$ 3,267,179	$ 21	$ 3,939,842	$ (671,779)	$ (905)
Ending Balance (in shares) at Dec. 31, 2018		203,904,265

Consolidated Statements of Sh_2

Consolidated Statements of Shareholders' Equity (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
Statement of Stockholders' Equity [Abstract]
Senior notes, issuance costs	$ 2,047
Capital stock, issuance costs	$ 13,425

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net loss	$ (119,858)	$ (94,420)	$ (220,438)
Adjustments to reconcile net loss to net cash provided by operating activities, net of amounts assumed in connection with acquisitions:
Depreciation and amortization	99,391	110,155	100,590
Share-based compensation expense	149,084	113,571	106,918
Amortization of contract cost assets	36,013	0	0
Gain on debt extinguishment	0	0	22,757
Amortization of discount and issuance costs on 2021 and 2023 Notes	26,672	18,012	883
Impairment costs	79,000	174,000	0
Deferred income taxes	(31,102)	(89,586)	(1,370)
Loss on disposal of property and equipment	3,617	5,678	3,689
Gain on divestiture of businesses, net	0	0	(1,360)
Bad debt expense	869	7,349	2,681
Deferred rent	(2,045)	7,085	1,730
Amortization (accretion) of bond premium (discount)	(4,313)	431	1,489
Changes in operating assets and liabilities:
Accounts receivable	(12,556)	(21,203)	(13,324)
Inventory	(162,829)	0	0
Mortgage loans held for sale	(1,161)	0	0
Prepaid expenses and other assets	(34,068)	10,807	(13,260)
Contract cost assets	(41,510)	0	0
Accounts payable	1,311	(373)	856
Accrued expenses and other current liabilities	1,920	19,000	(5,065)
Accrued compensation and benefits	11,291	(4,948)	12,463
Deferred revenue	2,162	2,633	7,794
Other long-term liabilities	1,962	0	1,612
Net cash provided by operating activities	3,850	258,191	8,645
Investing activities
Proceeds from maturities of investments	399,228	259,227	199,369
Proceeds from maturities of investments	(901,761)	(407,032)	(175,210)
Proceeds from sales of investments	13,567	0	4,963
Purchases of property and equipment	(66,054)	(66,728)	(62,060)
Purchases of intangible assets	(12,481)	(11,907)	(9,662)
Purchases of cost method investments	0	(10,000)	(10,000)
Proceeds from divestiture of businesses	0	579	3,200
Cash paid for acquisitions, net	(55,138)	(11,533)	(16,319)
Net used in investing activities	(622,639)	(247,394)	(65,719)
Financing activities
Proceeds from issuance of 2021 Notes, net of issuance costs	364,020	0	447,784
Premiums paid for Capped Call Confirmations	(29,414)	0	(36,616)
Proceeds from issuance of Class C Capital Stock, net of issuance costs	360,345	0	0
Proceeds from borrowing on revolving credit facility	116,700	0	0
Proceeds from borrowing on warehouse lines of credit	482	0	0
Partial repurchase of 2020 Notes	0	0	(370,235)
Proceeds from exercise of stock options	120,074	98,071	31,211
Value of equity awards withheld for tax liability	(70)	(365)	(616)
Contingent merger consideration	(2,000)	0	0
Net cash provided by financing activities	930,137	97,706	71,528
Net increase in cash and cash equivalents during period	311,348	108,503	14,454
Cash and cash equivalents at beginning of period	352,095	243,592	229,138
Cash, cash equivalents and restricted cash at end of period	663,443	352,095	243,592
Supplemental disclosures of cash flow information
Cash paid for interest	15,473	9,198	6,325
Noncash transactions:
Capitalized share-based compensation	8,590	11,236	10,061
Write-off of fully depreciated property and equipment	22,364	15,004	14,564
Write-off of fully amortized intangible assets	$ 12,999	$ 5,473	$ 9,293

Organization and Description of

Organization and Description of Business	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Organization and Description of Business	Organization and Description of Business Zillow Group, Inc. operates the largest portfolio of real estate and home-related brands on mobile and the web which focus on all stages of the home lifecycle: renting, buying, selling and financing. Zillow Group is committed to empowering consumers with unparalleled data, inspiration and knowledge around homes and connecting them with great real estate professionals. The Zillow Group portfolio of consumer brands includes Zillow, Trulia, Mortgage Lenders of America, L.L.C. (“MLOA”), StreetEasy, HotPads, Naked Apartments, RealEstate.com and Out East. In addition, Zillow Group provides a comprehensive suite of marketing software and technology solutions to help real estate professionals maximize business opportunities and connect with millions of consumers. Beginning in April 2018, Zillow Offers provides homeowners in certain metropolitan areas with the opportunity to receive offers to purchase their home from Zillow. When Zillow buys a home, it makes certain repairs and lists the home for resale on the open market. Beginning in October 2018, Zillow also provides consumers with the opportunity to receive mortgage financing through MLOA, a licensed mortgage lender. Zillow Group operates a number of business brands for real estate, rental and mortgage professionals, including Mortech, dotloop, Bridge Interactive and New Home Feed. Zillow, Inc. was incorporated as a Washington corporation in December 2004, and we launched the initial version of our website, Zillow.com, in February 2006. Zillow Group, Inc. was incorporated as a Washington corporation in July 2014 in connection with our acquisition of Trulia, Inc. (“Trulia”). Upon the closing of the Trulia acquisition in February 2015, each of Zillow, Inc. and Trulia became wholly owned subsidiaries of Zillow Group. Certain Significant Risks and Uncertainties

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements include Zillow Group, Inc. and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. These consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles (“GAAP”). Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make certain estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and the related disclosures at the date of the financial statements, as well as the reported amounts of revenue and expenses during the periods presented. On an ongoing basis, we evaluate our estimates, including those related to the net realizable value of inventory, amortization period and recoverability of contract cost assets, website and software development costs, recoverability of long-lived assets and intangible assets with definite lives, share-based compensation, income taxes, business combinations, and the recoverability of goodwill and indefinite-lived intangible assets, among others. To the extent there are material differences between these estimates, judgments, or assumptions and actual results, our financial statements will be affected. Concentrations of Credit Risk Financial instruments, which potentially subject us to concentrations of credit risk, consist primarily of cash and cash equivalents, investments, accounts receivable and mortgage loans held for sale. We place cash and cash equivalents and investments with major financial institutions, which management assesses to be of high credit quality, in order to limit exposure of our investments. Credit risk with respect to accounts receivable is dispersed due to the large number of customers. There were no customers that comprised 10% or more of our total accounts receivable as of December 31, 2018 and 2017 . Further, our credit risk on accounts receivable is mitigated by the relatively short payment terms that we offer. Collateral is not required for accounts receivable. We maintain an allowance for doubtful accounts such that receivables are stated at net realizable value. Similarly, our credit risk on mortgage loans held for sale is dispersed due to a large number of customers. Further, our credit risk on mortgage loans held for sale is mitigated by the fact that we typically sell mortgages on the secondary market within a relatively short period of time after the loan is originated. Cash and Cash Equivalents Cash includes demand deposits with banks or financial institutions. Cash equivalents include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Our cash equivalents include only investments with original maturities of three months or less. We regularly maintain cash in excess of federally insured limits at financial institutions. Short-term Investments Our investments consist of fixed income securities, which include U.S. and foreign government agency securities, corporate notes and bonds, commercial paper, municipal securities and certificates of deposit, and are classified as available-for-sale securities. As the investments are available to support current operations, our available-for-sale securities are classified as short-term investments. Available-for-sale securities are carried at fair value with unrealized gains and losses reported as a component of accumulated other comprehensive loss in shareholders’ equity, while realized gains and losses and other-than-temporary impairments are reported as a component of net loss based on specific identification. An impairment charge is recorded in the consolidated statements of operations for declines in fair value below the cost of an individual investment that are deemed to be other than temporary. We assess whether a decline in value is temporary based on the length of time that the fair market value has been below cost, the severity of the decline and the intent and ability to hold or sell the investment. We did no t identify any investments as other-than-temporarily impaired as of December 31, 2018 or 2017 . Restricted Cash Restricted cash consists of amounts funded to the reserve and collection accounts related to our Revolving Credit Facility (see Note 14 ) and amounts held in escrow related to funding home purchases in our mortgage originations business. Accounts Receivable and Allowance for Doubtful Accounts Accounts receivable represent our unconditional right to consideration. Accounts receivable are generally due within 30 days and are recorded net of the allowance for doubtful accounts. We consider accounts outstanding longer than the contractual terms past due. We review accounts receivable on a regular basis and estimate an amount of losses for uncollectible accounts based on our historical collections experience, age of the receivable, knowledge of the customer and the condition of the general economy and industry as a whole. We record changes in our estimate to the allowance for doubtful accounts through bad debt expense and relieve the allowance when accounts are ultimately determined to be uncollectible. Bad debt expense is included in general and administrative expenses. Mortgage Loans Held for Sale Mortgage loans held for sale includes residential mortgages originated for sale in the secondary market in connection with our October 2018 acquisition of MLOA. We have elected the fair value option for all mortgage loans held for sale as election of this option allows for a better offset of the changes in fair values of the loans and the derivative instruments used to economically hedge them without having to apply complex hedge accounting provisions. Mortgage loans held for sale are initially recorded at fair value based on either sale commitments or current market quotes and are adjusted for subsequent changes in fair value until the loans are sold. Net origination costs and fees associated with mortgage loans are recognized at the time of origination. We sell substantially all of the mortgages we originate and the related servicing rights to third-party purchasers. Interest income is earned from the date a mortgage loan is originated until the loan is sold and is classified within other income in the consolidated statements of operations. Substantially all of the mortgage loans originated are sold within a short period of time in the secondary mortgage market on a servicing released, nonrecourse basis, which limits exposure to nonperformance by loan buyer counterparties although we remain liable for certain limited representations and warranties related to loan sales, such as non-compliance with defined loan origination or documentation standards, including misstatement in the loan documents, early payoff or default on payments. Mortgage investors could seek to have us buy back loans or compensate them for losses incurred on mortgages we have sold based on claims that we breached our limited representations and warranties. We have established reserves for probable losses. Loan Commitments and Related Derivatives We are party to interest rate lock commitments (“IRLCs”), which are extended to borrowers who have applied for loan funding and meet defined credit and underwriting criteria in connection with our October 2018 acquisition of MLOA. IRLCs are accounted for as derivative instruments recorded at fair value with gains and losses recognized in revenue in the consolidated statements of operations. We manage our interest rate risk related to IRLCs and mortgage loans held for sale through the use of derivative instruments, generally forward contracts on mortgage-backed securities (“MBS”), which are commitments to either purchase or sell a specified financial instrument at a specified future date for a specified price, and mandatory loan commitments, which are an obligation by an investor to buy loans at a specified price within a specified time period. We do not enter into or hold derivatives for trading or speculative purposes and our derivatives are not designated as hedging instruments. Changes in the fair value of our derivative financial instruments are recognized in revenues in our consolidated statements of operations, and the fair values are reflected in other assets or other liabilities, as applicable. The net change in fair value was not significant for the year ended December 31, 2018. There are no credit-risk-related contingent features within our derivative agreements, and counterparty risk is considered minimal. Gains and losses on IRLCs are substantially offset by corresponding gains or losses on forward contracts on mortgage-backed securities and mandatory loan commitments. We are generally not exposed to variability in cash flows of derivative instruments for more than approximately 90 days. Inventory Inventory is comprised of homes acquired through our Zillow Offers program and is stated at the lower of cost or net realizable value. Homes are removed from inventory on a specific identification basis when they are resold. Stated cost includes consideration paid to acquire and update each home including associated allocated overhead costs. Work-in-progress inventory includes homes undergoing updates and finished goods inventory includes homes ready for resale. Unallocated overhead costs are expensed as incurred and included in cost of revenue. Selling costs, including commissions, escrow and title fees, staging, and holding costs, including utilities, taxes and maintenance, are expensed as incurred and included in sales and marketing expenses. Each quarter we review the value of homes held in inventory for indicators that net realizable value is lower than cost. When evidence exists that the net realizable value of inventory is lower than its cost, the difference is recognized in cost of revenue. Contract Cost Assets We capitalize certain incremental costs of obtaining contracts with customers which we expect to recover. These costs relate to commissions paid to sales personnel, primarily for our Premier Agent and Premier Broker programs. As a practical expedient, we recognize the incremental costs of obtaining a contract as an expense when incurred if the amortization period of the asset that we otherwise would have recognized is one year or less. Capitalized commission costs are recorded as contract cost assets in our consolidated balance sheets. Contract cost assets are amortized to expense on a straight-line basis over a period that is consistent with the transfer to the customer of the products or services to which the asset relates, generally the estimated life of the customer relationship. Amortization expense related to contract cost assets is included in sales and marketing expenses in our consolidated statements of operations. In determining the estimated life of our customer relationships, we consider quantitative and qualitative data, including, but not limited to, historical customer data, recent changes or expected changes in product or service offerings, and changes in how we monetize our products and services. The amortization period for capitalized contract costs related to our Premier Agent and Premier Broker programs ranges from two to three years. Property and Equipment Property and equipment is recorded at cost and depreciated using the straight-line method over the estimated useful lives of the related assets. The useful lives are as follows: Computer equipment 2 to 3 years Office equipment, furniture and fixtures 5 to 7 years Leasehold improvements Shorter of expected useful life or lease term Maintenance and repair costs are charged to expense as incurred. Major improvements, which extend the useful life of the related asset, are capitalized. Upon disposal of a fixed asset, we record a gain or loss based on the difference between the proceeds received and the net book value of the disposed asset. Website and Software Development Costs The costs incurred in the preliminary stages of development are expensed as incurred. Once an application has reached the development stage, internal and external costs, if direct and incremental and deemed by management to be significant, are capitalized in property and equipment and amortized on a straight-line basis over their estimated useful lives. Maintenance and enhancement costs, including those costs in the post-implementation stages, are typically expensed as incurred, unless such costs relate to substantial upgrades and enhancements to the website or software that result in added functionality, in which case the costs are capitalized and amortized on a straight-line basis over the estimated useful lives. Amortization expense related to capitalized website and software development costs is included in technology and development expense. Capitalized development activities placed in service are amortized over the expected useful lives of those releases, currently estimated at one to three years . The estimated useful lives of website and software development activities are reviewed frequently and adjusted as appropriate to reflect upcoming development activities that may include significant upgrades and/or enhancements to the existing functionality. Construction-in-progress primarily consists of website development costs that are capitalizable, but for which the associated applications had not been placed in service. Recoverability of Goodwill and Indefinite-Lived Intangible Assets Goodwill represents the excess of the cost of an acquired business over the fair value of the assets acquired at the date of acquisition, and is not amortized. We assess the impairment of goodwill on an annual basis, in our fourth quarter, or whenever events or changes in circumstances indicate that goodwill may be impaired. Typically, we choose to forgo the initial qualitative assessment and perform a quantitative analysis to assist in our annual evaluation. If impairment exists, the carrying value of the goodwill is reduced to fair value through an impairment charge recorded in our statements of operations. Our indefinite-lived intangible asset is not amortized, and we assess the asset for impairment on an annual basis, in our fourth quarter, or whenever events or changes in circumstances indicate that the asset may be impaired. On an interim basis we consider if there are any events and circumstances that could affect the significant inputs used to determine the fair value of the indefinite-lived intangible asset, including, but not limited to, costs that could have a negative effect on future expected earnings and cash flows, changes in certain key performance metrics, and changes in management, key personnel, strategy or customers. In our evaluation of our trade names and trademarks indefinite-lived intangible asset, we typically first perform a qualitative assessment to determine whether the fair value of the indefinite-lived intangible asset is more likely than not impaired. If so, we perform a quantitative assessment and an impairment charge is recorded in our statements of operations for the excess of the carrying value of the indefinite-lived intangible asset over its fair value. During the years ended December 31, 2018 and December 31, 2017, we recorded non-cash impairments for $69.0 million and $174.0 million related to the indefinite-lived Trulia trade names and trademarks intangible asset. For additional information about the non-cash impairments, see Note 11 to our consolidated financial statements. Intangible Assets We purchase and license data content from multiple data providers. This data content consists of U.S. county data about home details (e.g., the number of bedrooms, bathrooms, square footage) and other information relating to the purchase price of homes, both current and historical, as well as imagery, mapping and parcel data that is displayed on our mobile applications and websites. Our home details data not only provides information about a home and its related transactions which is displayed on our mobile applications and websites, but is also used in our proprietary valuation algorithms to produce Zestimates, Rent Zestimates and Zillow Home Value Indexes. License agreement terms vary by vendor. In some instances, we retain perpetual rights to this information after the contract ends; in other instances, the information and data are licensed only during the fixed term of the agreement. Additionally, certain data license agreements provide for uneven payment amounts throughout the contract term. We capitalize payments made to third parties for data licenses that we expect to provide future economic benefit through the recovery of the costs of these arrangements via the generation of our revenue and margins. For data license contracts that include uneven payment amounts, we capitalize the payments as they are made as an intangible asset and the total contract value is typically amortized on a straight-line basis over the term of the contract, which is equivalent to the estimated useful life of the asset. We evaluate data content contracts for potential capitalization at the inception of the arrangement as well as each time periodic payments to third parties are made. The amortization period for the capitalized purchased content is based on our best estimate of the useful life of the asset, which is approximately five years . The determination of the useful life includes consideration of a variety of factors including, but not limited to, our assessment of the expected use of the asset and contractual provisions that may limit the useful life, as well as an assessment of when the data is expected to become obsolete based on our estimates of the diminishing value of the data over time. We evaluate the useful life of the capitalized purchased data content each reporting period to determine whether events and circumstances warrant a revision to the remaining useful life. If we determine the estimate of the asset’s useful life requires modification, the carrying amount of the asset is amortized prospectively over the revised useful life. The capitalized purchased data content is amortized on a straight-line basis as the pattern of delivery of the economic benefits of the data cannot reliably be determined because we do not have the ability to reliably predict future traffic to our mobile applications and websites. Under certain other data agreements, the underlying data is obtained on a subscription basis with consistent monthly or quarterly recurring payment terms over the contractual period. Upon the expiration of such arrangements, we no longer have the right to access the related data, and therefore, the costs incurred under such contracts are not capitalized and are expensed as payments are made. We would immediately lose rights to data under these arrangements if we were to cancel the subscription and/or cease making payments under the subscription arrangements. We also capitalize costs related to the license of certain internal-use software from third parties, including certain licenses of software in cloud computing arrangements. Additionally, we capitalize costs incurred during the application development stage related to the development of internal-use software and enterprise cloud computing services. We expense costs as incurred related to the planning and post-implementation phases of development. Capitalized internal-use software costs are amortized over the estimated useful life of the asset, which is currently one to 3 years , on a straight-line basis. Intangibles-in-progress consist of purchased content and software that are capitalizable but have not been placed in service. We also have intangible assets for developed technology, customer relationships, trade names and trademarks and advertising relationships which we recorded in connection with acquisitions. Purchased intangible assets with a determinable economic life are carried at cost, less accumulated amortization. These intangible assets are amortized over the estimated useful life of the asset on a straight-line basis. Recoverability of Intangible Assets with Definite Lives and Other Long-Lived Assets We evaluate intangible assets and other long-lived assets for impairment whenever events or circumstances indicate that they may not be recoverable. Recoverability is measured by comparing the carrying amount of an asset group to future undiscounted net cash flows expected to be generated. We group assets for purposes of such review at the lowest level for which identifiable cash flows of the asset group are largely independent of the cash flows of the other groups of assets and liabilities. If this comparison indicates impairment, the amount of impairment to be recognized is calculated as the difference between the carrying value and the fair value of the asset group. Deferred Revenue Deferred revenue consists of prepaid advertising fees received or billed in advance of satisfying our performance obligations and prepaid but unrecognized subscription revenue. Deferred revenue is recognized when or as we satisfy our obligations under contracts with customers. Deferred Rent For our operating leases, we recognize rent expense on a straight-line basis over the terms of the leases and, accordingly, we record the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. For office space under an operating lease that is subleased to a third party for which we intend to reoccupy the space at a future date, rent expense is recognized net of sublease income. Landlord-funded leasehold improvements are also recorded as deferred rent liabilities and are amortized as a reduction of rent expense over the non-cancelable term of the related operating lease. Business Combinations We recognize identifiable assets acquired and liabilities assumed at their acquisition date fair values. Goodwill as of the acquisition date is measured as the excess of consideration transferred over the net of the acquisition date fair values of the assets acquired and the liabilities assumed. While we use our best estimates and assumptions for the purchase price allocation process to value assets acquired and liabilities assumed at the acquisition date, our estimates are inherently uncertain and subject to refinement. As a result, during the measurement period, which may be up to one year from the acquisition date, we record adjustments to the assets acquired and liabilities assumed, with the corresponding offset to goodwill to the extent that we identify adjustments to the preliminary purchase price allocation. Upon the conclusion of the measurement period or final determination of the values of assets acquired or liabilities assumed, whichever comes first, any subsequent adjustments are recorded to our consolidated statements of operations. We recognize adjustments to provisional amounts that are identified during the measurement period in the reporting period in which the adjustment amounts are determined. Revenue Recognition We recognize revenue when (or as) we satisfy our performance obligations by transferring control of the promised products or services to our customers in an amount that reflects the consideration to which we expect to be entitled in exchange for those products or services. As a practical expedient, we do not adjust the promised amount of consideration for the effects of a significant financing component as the period between our transfer of a promised product or service to a customer and when the customer pays for that product or service is one year or less. We do not disclose the transaction price related to remaining performance obligations for (i) contracts with an original expected duration of one year or less and (ii) contracts for which we recognize revenue at the amount to which we have the right to invoice for performance completed to date. The remaining duration of our performance obligations is generally less than one year. In our Internet, Media & Technology (“IMT”) segment, we generate revenue from the sale of advertising services and our suite of marketing software and technology solutions to businesses and professionals primarily associated with the residential real estate, rental and mortgage industries. These professionals include real estate, rental and mortgage professionals and brand advertisers. Our four primary revenue categories within our IMT segment are Premier Agent, Rentals, Mortgages and Other. In our Homes segment, we generate revenue from the resale of homes on the open market through our Zillow Offers program. Premier Agent Revenue. Premier Agent revenue is derived from our Premier Agent and Premier Broker programs. Our Premier Agent and Premier Broker programs offer a suite of marketing and business technology products and services to help real estate agents and brokers achieve their advertising goals, while growing and managing their businesses and brands. All Premier Agents and Premier Brokers receive access to a dashboard portal on our mobile application or website that provides individualized program performance analytics, our customer relationship management, or CRM, tool that captures detailed information about each contact made with a Premier Agent or Premier Broker through our mobile and web platforms and our account management tools. We have concluded that the marketing and business technology products and services promised to Premier Agents and Premier Brokers represent distinct performance obligations. We primarily offer our Premier Agent and Premier Broker advertising products on a cost per impression basis. Payment is received prior to the delivery of impressions. Impressions are delivered when a sold advertisement appears on pages viewed by users of our mobile applications and websites. We determine the cost per impression delivered in each zip code using an auction-based pricing method in consideration of the total amount spent by Premier Agents and Premier Brokers to purchase impressions in the zip code during the month. A Premier Agent’s or Premier Broker’s share of voice in a zip code is determined by their proportional monthly budgeted spend in that zip code as a percentage of the total monthly budgeted spend of all Premier Agents and Premier Brokers in that zip code. The cost per impression that we charge is dynamic - as demand for impressions in a zip code increases or decreases, the cost per impression in that zip code may be increased or decreased accordingly. The price paid for each impression is representative of the price at which we would sell an impression separately to a customer, or the stand-alone selling price. We have not allocated the transaction price to each performance obligation as the amounts recognized would be the same irrespective of any allocation. As such, we recognize revenue related to the Premier Agent and Premier Broker products and services based on the contractual spend recognized on a straight-line basis during the contractual period over which the products and services are provided. This methodology best depicts how we satisfy our performance obligations to customers, as we continuously transfer control of the performance obligations to the customer throughout the contractual period. In October 2018, we began testing a new Flex Pricing model for Premier Broker and Premier Agent advertising services in limited markets. With the Flex Pricing model, Premier Brokers and Premier Agents are provided with validated leads at no upfront cost, and they pay a performance advertising fee only when a real estate transaction is closed with one of their leads. With this pricing model, the transaction price represents variable consideration as the amount to which we expect to be entitled varies based on the number of validated leads that convert into real estate transactions. Rentals Revenue. Rentals revenue includes our rentals marketplace and suite of tools for rental professionals. Rentals revenue primarily includes revenue generated by advertising sold to property managers and other rental professionals on a cost per lead, cost per click or cost per lease generated basis. We recognize revenue as leads or clicks are provided to rental professionals, which is the amount for which we have the right to invoice. The number of leases generated through our rentals marketplace during the period is accounted for as variable consideration, and we estimate these amounts based on the expected number of qualified leases secured during the period. We do not believe that a significant reversal in the amount of cumulative revenue recognized will occur once the uncertainty related to the number of leases secured is subsequently resolved. Beginning in 2018, rentals revenue also includes revenue generated from Zillow’s rental applications product through which potential renters can submit applications to multiple rental properties over a 30-day period for a flat service fee. We recognize revenue for the rental applications product on a straight-line basis during the contractual period over which the customer has the right to access and submit the rental application. Mortgages Revenue. Mortgages revenue primarily includes marketing products sold to mortgage professionals on a cost per lead basis, including our Custom Quote and a portion of our Connect (formerly known as Long Form) services, and on a subscription basis, including a portion of our Connect service. For our Connect and Custom Quote cost per lead mortgage marketing products, participating qualified mortgage professionals typically make a prepayment to gain access to consumers interested in connecting with mortgage professionals. Mortgage professionals who exhaust their initial prepayment prepay additional funds to continue to participate in the marketplace. For our Connect subscription mortgage marketing product, participating qualified mortgage professionals generally prepay a monthly subscription fee, which they then allocate to desired geographic counties. In Zillow Group’s Connect platform, consumers answer a series of questions to find a local lender, and mortgage professionals receive consumer contact information, or leads, when the consumer chooses to share their information with a lender. Consumers who request rates for mortgage loans in Custom Quotes are presented with customized quotes from participating mortgage professionals. For our cost per lead mortgages products, we recognize revenue when a user contacts a mortgage professional through Zillow Group’s mortgages platform, which is the amount for which we have the right to invoice. For our Connect subscription product, the opportunity to receive a consumer contact is based on the mortgage professional’s relative share of voice in a geographic county. When a consumer submits a contact, Zillow Group contacts a group of subscription mortgage professionals via text message, and the first mortgage professional to respond receives the consumer contact information. We recognize revenue based on the contractual spend recognized on a straight-line basis during the contractual period over which the service is provided. This methodology best depicts how we satisfy our performance obligation to subscription customers, as we continuously transfer control of the performance obligation to the customer throughout the contractual period. Beginning in October 2018, mortgages revenue also includes revenue generated from our mortgage originations business. We elect the fair value option for our mortgage loans held for sale, which are initially recorded at fair value based on either sale commitments or current market quotes and are adjusted for subsequent changes in fair value until the loans are closed. Mortgages revenue also includes revenue generated by Mortech, which provides subscription-based mortgage software solutions, including a product and pricing engine and lead management platform, for which we recognize revenue on a straight-line basis during the contractual period over which the services are provided. Other Revenue. Other revenue primarily includes revenue generated by new construction and display, as well as revenue from the sale of various other marketing and business products and services to real estate professionals. Our new construction marketing solutions allow home builders to showcase their available inventory to home shoppers. New construction revenue primarily includes reven

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	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 —The fair value measurement of money market funds is based on quoted market prices in active markets. The fair value measurement of corporate notes and bonds, commercial paper, U.S. government agency securities and certificates of deposit 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. Short-term investments —The fair value measurement of our short-term investments 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. Restricted cash —The carrying value of restricted cash approximates fair value due to the short period of time amounts borrowed on the Revolving Credit Facility (see Note 14 ) are outstanding. Further, the carrying value of restricted cash related to escrow amounts held as part of the mortgage originations business also approximates fair value due to the short period of time amounts are held in escrow before they are transferred to the appropriate party, typically a home seller or bank. Mortgage loans held for sale —The fair value of mortgage loans held for sale is generally calculated by reference to quoted prices in secondary markets for commitments to sell mortgage loans with similar characteristics. Interest rate lock commitments —The fair value of interest rate lock commitments is calculated by reference to quoted prices in secondary markets for commitments to sell mortgage loans with similar characteristics. Any expired commitments are excluded from the fair value measurement. We generally only issue IRLCs for products that meet specific purchaser guidelines. Since not all IRLCs will become closed loans, we adjust our fair value measurements for the estimated amount of IRLCs that will not close. Forward contracts —The fair value of mandatory loan sales commitments and derivative instruments such as forward sales of MBS that are utilized as hedging instruments are calculated by reference to quoted prices for similar assets. The following tables present the balances of assets measured at fair value on a recurring basis, by level within the fair value hierarchy, as of the dates presented (in thousands): December 31, 2018 Total Level 1 Level 2 Cash equivalents: Money market funds $ 541,575 $ 541,575 $ — Commercial paper 3,999 — 3,999 Short-term investments: U.S. government agency securities 646,496 — 646,496 Corporate notes and bonds 112,933 — 112,933 Commercial paper 85,506 — 85,506 Municipal securities 39,306 — 39,306 Foreign government securities 14,915 — 14,915 Certificates of deposit 4,711 — 4,711 Mortgage origination-related: Mortgage loans held for sale 35,409 — 35,409 Interest rate lock commitments 847 — 847 Forward contracts (125 ) — (125 ) Total $ 1,485,572 $ 541,575 $ 943,997 December 31, 2017 Total Level 1 Level 2 Cash equivalents: Money market funds $ 233,508 $ 233,508 $ — Corporate notes and bonds 6,199 — 6,199 Commercial paper 3,987 — 3,987 U.S. government agency securities 1,748 — 1,748 Certificates of deposit 249 — 249 Short-term investments: U.S. government agency securities 298,758 — 298,758 Corporate notes and bonds 44,607 — 44,607 Commercial paper 39,325 — 39,325 Municipal securities 11,459 — 11,459 Certificates of deposit 10,297 — 10,297 Foreign government securities 5,998 — 5,998 Total $ 656,135 $ 233,508 $ 422,627 At December 31, 2018 , the notional amounts of the hedging instruments related to our mortgage loans held for sale were $26.7 million and $28.8 million for our interest rate lock commitments and forward contracts, respectively. See Note 14 for the carrying amount and estimated fair value of the Company’s Convertible Senior Notes due in 2023, Convertible Senior Notes due in 2021 and Trulia’s Convertible Senior Notes due in 2020. We did no t have any Level 3 assets as of December 31, 2018 or 2017 . There were no material liabilities measured at fair value as of December 31, 2018 or 2017

Cash and Cash Equivalents, Shor

Cash and Cash Equivalents, Short-term Investments and Restricted Cash	12 Months Ended
	Dec. 31, 2018
Cash and Cash Equivalents [Abstract]
Cash and Cash Equivalents, Short-term Investments and Restricted Cash	Cash and Cash Equivalents, Short-term Investments and Restricted Cash The following tables present the amortized cost, gross unrealized gains and losses and estimated fair market value of our cash and cash equivalents, available-for-sale investments and restricted cash as of the dates presented (in thousands): December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Market Value Cash $ 105,484 $ — $ — $ 105,484 Cash equivalents: Money market funds 541,575 — — 541,575 Commercial paper 3,999 — — 3,999 Short-term investments: U.S. government agency securities 647,266 51 (821 ) 646,496 Corporate notes and bonds 113,109 1 (177 ) 112,933 Commercial paper 85,506 — — 85,506 Municipal securities 39,316 23 (33 ) 39,306 Foreign government securities 14,929 — (14 ) 14,915 Certificates of deposit 4,711 1 (1 ) 4,711 Restricted cash 12,385 — — 12,385 Total $ 1,568,280 $ 76 $ (1,046 ) $ 1,567,310 December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Market Value Cash $ 106,404 $ — $ — $ 106,404 Cash equivalents: Money market funds 233,508 — — 233,508 Corporate notes and bonds 6,200 — (1 ) 6,199 Commercial paper 3,987 — — 3,987 U.S. government agency securities 1,748 — — 1,748 Certificates of deposit 249 — — 249 Short-term investments: U.S. government agency securities 299,814 — (1,056 ) 298,758 Corporate notes and bonds 44,661 1 (55 ) 44,607 Commercial paper 39,325 — — 39,325 Municipal securities 11,494 — (35 ) 11,459 Certificates of deposit 10,296 2 (1 ) 10,297 Foreign government securities 6,000 — (2 ) 5,998 Total $ 763,686 $ 3 $ (1,150 ) $ 762,539 The following table presents available-for-sale investments by contractual maturity date as of December 31, 2018 (in thousands): Amortized Cost Estimated Fair Market Value Due in one year or less $ 801,828 $ 800,827 Due after one year through two years 103,009 103,040 Total $ 904,837 $ 903,867

Accounts Receivable, Net

Accounts Receivable, Net	12 Months Ended
	Dec. 31, 2018
Receivables [Abstract]
Accounts Receivable, Net	Accounts Receivable, Net The following table presents the detail of accounts receivable as of the dates presented (in thousands): December 31, 2018 2017 Accounts receivable $ 61,134 $ 51,334 Unbilled accounts receivable 9,787 8,403 Less: allowance for doubtful accounts (4,838 ) (5,341 ) Accounts receivable, net $ 66,083 $ 54,396 The following table presents the changes in the allowance for doubtful accounts for the periods presented (in thousands): Year Ended December 31, 2018 2017 2016 Allowance for doubtful accounts: Balance, beginning of period $ 5,341 $ 1,337 $ 3,378 Additions charged to expense 869 7,349 2,681 Less: write-offs, net of recoveries and other adjustments (1,372 ) (3,345 ) (4,722 ) Balance, end of period $ 4,838 $ 5,341 $ 1,337

Inventory

Inventory	12 Months Ended
	Dec. 31, 2018
Inventory Disclosure [Abstract]
Inventory	Inventory The components of inventory, net of applicable lower of cost or net realizable value write-downs, were as follows for the periods presented (in thousands): December 31, 2018 2017 Work-in-progress $ 45,943 $ — Finished goods 116,886 — Inventory $ 162,829 $ —

Contract Cost Assets

Contract Cost Assets	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Contract Cost Assets	Contract Cost Assets As of December 31, 2018 , we had $45.8 million of contract cost assets. During the year ended December 31, 2018 , we recorded no impairment losses to contract cost assets. During the year ended December 31, 2018 , we recorded $36.0 million The following table presents the change in deferred revenue for the period presented (in thousands): Year Ended December 31, 2018 Balance as of January 1, 2018 $ 31,918 Deferral of revenue 982,647 Less: Revenue recognized (980,485 ) Balance as of December 31, 2018 $ 34,080 During the year ended December 31, 2018 , we recognized as revenue a total of $28.8 million pertaining to amounts that were recorded in deferred revenue as of December 31, 2017

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	Property and Equipment, Net The following table presents the detail of property and equipment as of the dates presented (in thousands): December 31, 2018 2017 Website development costs $ 149,891 $ 130,072 Computer equipment 22,477 30,071 Leasehold improvements 65,012 47,321 Construction-in-progress 29,037 28,150 Office equipment, furniture and fixtures 39,510 22,887 Property and equipment 305,927 258,501 Less: accumulated amortization and depreciation (170,755 ) (146,230 ) Property and equipment, net $ 135,172 $ 112,271 We recorded depreciation expense related to property and equipment (other than website development costs) of $19.5 million , $15.6 million and $13.5 million , respectively, during the years ended December 31, 2018 , 2017 and 2016 . We capitalized $34.1 million , $49.9 million and $49.5 million , respectively, in website development costs during the years ended December 31, 2018 , 2017 and 2016 . Amortization expense for website development costs included in technology and development expenses was $28.6 million , $40.0 million and $40.0 million , respectively, for the years ended December 31, 2018 , 2017 and 2016

Acquisitions and Equity Investm

Acquisitions and Equity Investments	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Acquisitions and Equity Investments	Acquisitions and Equity Investments Acquisition of Mortgage Lenders of America On October 31, 2018, Zillow Group’s wholly owned subsidiary, ZGM Holdco, Inc., acquired the outstanding equity of Mortgage Lenders of America, L.L.C., a national mortgage lender headquartered in Overland Park, Kansas for approximately $66.7 million in cash. Our acquisition of MLOA has been accounted for as a business combination, and assets acquired and liabilities assumed were recorded at their estimated fair values as of October 31, 2018. 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 goodwill recognized in conjunction with this business combination has been allocated to our IMT segment. The total purchase price has been allocated to the assets acquired and liabilities assumed, including identifiable intangible assets, based on their respective fair values at the acquisition date. Based upon the fair values determined by us, in which we considered or relied in part upon a valuation report of a third-party expert, the total purchase price was allocated as follows (in thousands): Cash and cash equivalents $ 10,796 Restricted cash 753 Mortgage loans available for sale 34,248 Property, plant and equipment 1,315 Intangible assets 2,600 Goodwill 53,831 Other acquired assets 3,079 Accounts payable (1,953 ) Accrued expenses (2,591 ) Warehouse lines of credit (32,536 ) Other assumed liabilities (2,855 ) Total purchase price $ 66,687 Acquisition-related costs incurred, which primarily included legal, accounting, regulatory and other external costs directly related to the acquisition, are included within Acquisition-related costs within our consolidated statements of operations and were expensed as incurred. The results of operations related to the acquisition of MLOA have been included in our consolidated financial statements since the date of acquisition, and are not significant. On an unaudited pro forma basis, revenue would have been approximately 3.0% higher for the year ended December 31, 2018 and 5.0% higher for the year-ended December 31, 2017 if the acquisition would have been consummated as of January 1, 2017. Unaudited pro forma earnings information has not been presented as the effects were not material to our consolidated financial statements. Acquisition of New Home Feed On September 6, 2017, Zillow, Inc. acquired New Home Feed, Inc. (formerly known as Graphic Language, Inc.) , a California corporation which operates the New Home Feed business, pursuant to an Agreement and Plan of Merger for an immaterial amount. New Home Feed is a listing management technology that allows builders to input, manage and syndicate their listings across Zillow Group and partner sites. Our acquisition of New Home Feed has been accounted for as a business combination, and assets acquired and liabilities assumed were recorded at their estimated fair values as of September 6, 2017. We acquired goodwill of $3.6 million and an identifiable intangible asset of $1.9 million . Acquisition-related costs incurred related to the acquisition of New Home Feed, which primarily included legal and accounting fees and other external costs directly related to the acquisition, were expensed as incurred and were not material. The results of operations related to the acquisition of New Home Feed have been included in our consolidated financial statements since the date of acquisition and are not significant. Pro forma financial information for the acquisition accounted for as a business combination has not been presented, as the effects were not material to our consolidated financial statements. Acquisition of Hamptons Real Estate Online On January 11, 2017, Zillow, Inc. acquired substantially all of the operating assets of RealNet Solutions, Inc., a New York corporation, RealNetDB, LLC, a New York limited liability company, Hamptons Real Estate Online, Inc., a New York corporation, and HREO.com, LLC, a New York limited liability company (collectively, “HREO”), pursuant to an Asset Purchase Agreement entered into by Zillow, Inc., HREO, each of the equity owners of HREO, and an individual acting as representative of the HREO equity holders. HREO is a Hamptons-focused real estate portal which provides buyers and renters with a specialized search experience and access to the area’s most comprehensive for-sale, for-rent, and vacant land listings. HREO’s listing entry and distribution software, RealNet and Open RealNet Exchange, provides real estate professionals with tools to manage and market their listings. Our acquisition of HREO has been accounted for as a business combination, and assets acquired and liabilities assumed were recorded at their estimated fair values as of January 11, 2017. We acquired goodwill of $4.0 million , identifiable intangible assets of $2.1 million and net liabilities of approximately $0.1 million . Acquisition-related costs incurred related to the acquisition of HREO, which primarily included legal and accounting fees and other external costs directly related to the acquisition, were expensed as incurred and were not material. The results of operations related to the acquisition of HREO have been included in our consolidated financial statements since the date of acquisition and are not significant. Pro forma financial information for the acquisition accounted for as a business combination has not been presented, as the effects were not material to our consolidated financial statements. Acquisition of Bridge Interactive Group In July 2016, Zillow, Inc., Bridge Interactive Group, LLC, a Georgia limited liability company (“Bridge Interactive”), each of the members of Bridge Interactive, and an individual acting as the seller representative, entered into a Securities Purchase Agreement pursuant to which Zillow, Inc. acquired all of the outstanding ownership interests of Bridge Interactive on August 1, 2016. Bridge Interactive is a creator of broker and multiple listing service (MLS) back-office software. Our acquisition of Bridge Interactive has been accounted for as a business combination, and assets acquired and liabilities assumed were recorded at their estimated fair values as of August 1, 2016. Acquisition-related costs incurred, which primarily included legal and accounting fees and other external costs directly related to the acquisition, were expensed as incurred and were not material. The results of operations related to the acquisition of Bridge Interactive have been included in our consolidated financial statements since the date of acquisition and are not significant. Pro forma financial information for the acquisition accounted for as a business combination has not been presented, as the effects were not material to our consolidated financial statements. Acquisition of Naked Apartments In February 2016, Zillow, Inc., Nectarine Merger Sub, Inc., a Delaware corporation and wholly owned subsidiary of Zillow, Inc. (“Merger Sub”), Naked Apartments, Inc., a Delaware corporation (“Naked Apartments”), and an individual acting as the stockholder representative, entered into an Agreement and Plan of Merger (the “Naked Apartments Merger Agreement”), pursuant to which Zillow, Inc. acquired Naked Apartments on February 22, 2016 for approximately $13.2 million in cash. Under the terms and subject to the conditions of the Naked Apartments Merger Agreement, Merger Sub merged with and into Naked Apartments, with Naked Apartments remaining as the surviving company and a wholly owned subsidiary of Zillow, Inc. Naked Apartments is New York City’s largest rentals-only platform. Our acquisition of Naked Apartments has been accounted for as a business combination, and assets acquired and liabilities assumed were recorded at their estimated fair values as of February 22, 2016. 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 total purchase price has been allocated to the assets acquired and liabilities assumed, including identifiable intangible assets, based on their respective fair values at the acquisition date. Based upon the fair values determined by us, in which we considered or relied in part upon a valuation report of a third-party expert, the total purchase price was allocated as follows (in thousands): Current assets $ 371 Identifiable intangible assets 3,700 Goodwill 10,610 Current liabilities (101 ) Deferred tax liabilities (1,416 ) Total purchase price $ 13,164 Acquisition-related costs incurred, which primarily included legal and accounting fees and other external costs directly related to the acquisition, were expensed as incurred and were not material. The results of operations related to the acquisition of Naked Apartments have been included in our consolidated financial statements since the date of acquisition and are not significant. Pro forma financial information for the acquisition accounted for as a business combination has not been presented, as the effects were not material to our consolidated financial statements. Equity Investments In June 2017, we purchased an equity interest in a privately held corporation for approximately $10.0 million . In October 2016, we purchased a 10% equity interest in a privately held variable interest entity within the real estate industry for $10.0 million . The entity is financed through its business operations. We are not the primary beneficiary of the entity, as we do not direct the activities that most significantly impact the entity’s economic performance. Therefore, we do not consolidate the entity. Our maximum exposure to loss is $10.0 million , the carrying amount of the investment as of December 31, 2018 . These investments are equity securities without readily determinable fair values which we account for at cost minus any impairment, plus or minus changes resulting from observable price changes in orderly transactions for identical or similar investments of the same issuer. During the year ended December 31, 2018 , we recognized a non-cash impairment charge of $10.0 million related to our June 2017 investment. The impairment charge is included in Impairment costs within our consolidated statements of operations. During the third quarter of 2018, in connection with our quarterly qualitative assessment of this investment for impairment indicators, we identified factors that led us to conclude that the investment was impaired and the fair value of the investment was less than the carrying value. The most significant of such factors was related to the business prospects of the investee. Accordingly, we performed an analysis to determine the fair value of the investment and concluded that our best estimate of its fair value was $0.0 million . This is considered a Level 3 measurement under the fair value hierarchy. There has been no impairment or upward or downward adjustments for our October 2016 equity investment as of December 31, 2018

Goodwill

Goodwill	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	Goodwill The goodwill balance as of December 31, 2018 and 2017 is fully attributable to our IMT segment. The following table presents the change in goodwill from December 31, 2017 through December 31, 2018 (in thousands): Balance as of December 31, 2017 $ 1,931,076 Goodwill recorded in connection with acquisition of MLOA 53,831 Balance as of December 31, 2018 $ 1,984,907

Intangible Assets

Intangible Assets	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	Intangible Assets The following tables present the detail of intangible assets subject to amortization as of the dates presented (in thousands): December 31, 2018 Cost Accumulated Amortization Net Purchased content $ 42,110 $ (30,477 ) $ 11,633 Software 24,296 (13,925 ) 10,371 Customer relationships 103,900 (60,733 ) 43,167 Developed technology 111,980 (72,788 ) 39,192 Trade names and trademarks 4,900 (4,683 ) 217 MLOA lender licenses 400 (17 ) 383 Intangibles-in-progress 2,941 — 2,941 Total $ 290,527 $ (182,623 ) $ 107,904 December 31, 2017 Cost Accumulated Amortization Net Purchased content $ 35,260 $ (20,480 ) $ 14,780 Software 18,957 (8,899 ) 10,058 Customer relationships 103,900 (46,365 ) 57,535 Developed technology 113,380 (56,664 ) 56,716 Trade names and trademarks 4,900 (3,943 ) 957 Advertising relationships 9,000 (8,525 ) 475 Intangibles-in-progress 2,190 — 2,190 Total $ 287,587 $ (144,876 ) $ 142,711 Amortization expense recorded for intangible assets for the years ended December 31, 2018 , 2017 and 2016 was $50.8 million , $54.3 million and $47.0 million , respectively, and these amounts are included in technology and development expenses. Estimated future amortization expense for intangible assets, including amortization related to future commitments (see Note 19 ), as of December 31, 2018 is as follows (in thousands): 2019 $ 42,648 2020 39,420 2021 33,908 2022 5,480 2023 373 Total future amortization expense $ 121,829 We have an indefinite-lived intangible asset that we recorded in connection with our February 2015 acquisition of Trulia for Trulia’s trade names and trademarks that is not subject to amortization. The carrying value of the Trulia trade names and trademarks intangible asset was $108.0 million and $177.0 million , respectively, as of December 31, 2018 and 2017 . During the year ended December 31, 2018 , we recognized a non-cash impairment charge of $69.0 million related to our indefinite-lived Trulia trade names and trademarks intangible asset. The impairment charge is included in Impairment costs within our IMT segment. In connection with our annual budgeting process that was substantially completed during the three months ended December 31, 2018, we identified factors that led us to conclude it was more likely than not that the $177.0 million carrying value of the asset exceeded its fair value. The most significant of such factors was a shortfall in projected revenue related to the Trulia brand compared to projections at the time the intangible asset was remeasured as of October 1, 2017. Accordingly, with the assistance of a third-party valuation specialist, we performed a quantitative analysis to determine the fair value of the intangible asset and concluded that our best estimate of its fair value was $108.0 million . The valuation was prepared using an income approach based on the relief-from-royalty method and relied on inputs with unobservable market prices including the assumed revenue growth rates, royalty rate, discount rate, and estimated tax rate, and therefore is considered a Level 3 measurement under the fair value hierarchy. In connection with this impairment analysis, we evaluated our planned future use of the Trulia trade names and trademarks intangible asset and concluded that it remains appropriate to consider this asset to have an indefinite life. During the year ended December 31, 2017 , we recognized a non-cash impairment charge of $174.0 million related to our indefinite-lived Trulia trade names and trademarks intangible asset. The impairment charge is included in Impairment costs within our consolidated statements of operations. In connection with our qualitative assessment of the recoverability of this asset during our annual impairment test as of October 1, 2017, we identified factors that led us to conclude it was more likely than not that the $351.0 million carrying value of the asset exceeded its fair value. The most significant of such factors was a shortfall in projected revenue related to the Trulia brand compared to projections at the time the intangible asset was initially recorded in February 2015. Accordingly, with the assistance of a third-party valuation specialist, we performed a quantitative analysis to determine the fair value of the intangible asset and concluded that our best estimate of its fair value was $177.0 million

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	12 Months Ended
	Dec. 31, 2018
Payables and Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	Accrued Expenses and Other Current Liabilities The following table presents the detail of accrued expenses and other current liabilities as of the dates presented (in thousands): December 31, 2018 2017 Accrued marketing and advertising $ 18,559 $ 17,180 Accrued purchased content 4,256 5,984 Accrued estimated legal liabilities and legal fees 7,305 9,052 Merger consideration payable to former stockholders of certain acquired entities 5,904 5,904 Other accrued expenses and other current liabilities 27,077 23,253 Total accrued expenses and other current liabilities $ 63,101 $ 61,373

Deferred Revenue

Deferred Revenue	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Deferred Revenue	Contract Cost Assets As of December 31, 2018 , we had $45.8 million of contract cost assets. During the year ended December 31, 2018 , we recorded no impairment losses to contract cost assets. During the year ended December 31, 2018 , we recorded $36.0 million The following table presents the change in deferred revenue for the period presented (in thousands): Year Ended December 31, 2018 Balance as of January 1, 2018 $ 31,918 Deferral of revenue 982,647 Less: Revenue recognized (980,485 ) Balance as of December 31, 2018 $ 34,080 During the year ended December 31, 2018 , we recognized as revenue a total of $28.8 million pertaining to amounts that were recorded in deferred revenue as of December 31, 2017

Debt

Debt	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Debt	Debt Revolving Credit Facility On July 31, 2018, certain wholly owned subsidiaries of Zillow Group entered into a revolving credit agreement with Credit Suisse AG, Cayman Islands Branch, as the directing lender, and certain other parties thereto (the “Revolving Credit Facility”). The Revolving Credit Facility initially provided for a maximum borrowing capacity of $250.0 million , and this borrowing capacity was increased to $500.0 million effective December 31, 2018 (the “Maximum Amount”) and has a current borrowing capacity of $126.7 million as of December 31, 2018, which amount may be increased up to the Maximum Amount subject to the satisfaction of certain conditions, through a non-recourse credit facility secured by a pledge of the equity of certain Zillow Group subsidiaries that purchase and sell select residential properties through Zillow Offers. In certain circumstances Zillow Group may be obligated to fund some or all of the payment obligations under the Revolving Credit Facility. Zillow Group formed certain special purpose entities to effectuate the transactions contemplated by the agreement underlying the Revolving Credit Facility. Each special purpose entity is a wholly owned subsidiary of Zillow Group and a separate legal entity, and neither the assets nor credit of any such entity are available to satisfy the debts and other obligations of any affiliate or other entity. The Revolving Credit Facility has an initial term of one year which may be extended for up to two additional years subject to agreement by the directing lender. The Revolving Credit Facility includes customary representations and warranties, covenants (including financial covenants applicable to Zillow Group), and provisions regarding events of default. As of December 31, 2018 , Zillow Group was in compliance with all financial covenants and no event of default had occurred. Availability of funds under the Revolving Credit Facility is limited by a formula equal to the lower of 85% of the aggregate acquisition cost of financed residential properties or 85% of the aggregate market value, which for each residential property is the sum of the value established by an independent broker-pricing opinion and renovation costs paid. Pursuant to the terms of the Revolving Credit Facility, we are required to establish, maintain, and in certain circumstances fund, certain specified reserve accounts. These reserve accounts include, but are not limited to, interest reserves, insurance, tax reserves, renovation cost reserves and special reserves. The credit facility reserve accounts and the collection account into which funds are deposited upon the resale of financed residential properties, which funds are used to repay amounts borrowed on the Revolving Credit Facility, are under the sole control of Credit Suisse AG, New York Branch, as defined in the agreement governing the Revolving Credit Facility. Amounts funded to these reserve accounts and the collection account have been classified within our consolidated balance sheets as restricted cash. Borrowings on our Revolving Credit Facility bear interest at the one-month London Interbank Offered Rate (“LIBOR”) plus the applicable margin, as defined in the credit agreement governing the Revolving Credit Facility. We are also required to pay a funding fee for each financed residential property and certain other fees to certain other parties to the agreement. Interest, funding fees and other fees, including the amortization of deferred issuance costs, are classified within interest expense in our consolidated statements of operations. As of December 31, 2018 , we have outstanding $116.7 million of borrowings on the Revolving Credit Facility. The facility has a maximum borrowing capacity of $500.0 million with a current borrowing capacity of $126.7 million . Approximately $383.3 million is available for future borrowings. The weighted average interest rate related to the Revolving Credit Facility from July 31, 2018 through December 31, 2018 was 5.86% . Warehouse Lines of Credit As part of the acquisition of MLOA, Zillow Group acquired two warehouse lines of credit. Each line of credit provides for a current and maximum borrowing capacity of $50.0 million , or $100.0 million in total. The lines of credit mature on July 15, 2019 and March 31, 2019 and include customary representations and warranties, covenants and provisions regarding events of default. As of December 31, 2018 , Zillow Group was in compliance with all financial covenants and no event of default had occurred. Availability under the lines of credit is limited depending on the types of loans originated. Borrowings on the lines of credit bear interest at either the one-month LIBOR or the daily adjusting LIBOR, plus an applicable margin, as defined in the credit agreements governing the warehouse lines of credit. The weighted average interest rates on each of the lines of credit from the acquisition of MLOA through December 31, 2018 were 4.88% and 4.73% . Convertible Senior Notes due in 2023 On July 3, 2018, Zillow Group issued $373.8 million aggregate principal amount of Convertible Senior Notes due 2023 (the “2023 Notes”), which includes $48.8 million principal amount of 2023 Notes sold pursuant to the underwriters’ option to purchase additional 2023 Notes. The 2023 Notes bear interest at a fixed rate of 1.50% per year, payable semi-annually in arrears on January 1 and July 1 of each year, beginning on January 1, 2019. The 2023 Notes are convertible into cash, shares of Class C capital stock or a combination thereof, at our election. The 2023 Notes will mature on July 1, 2023, unless earlier repurchased, redeemed, or converted in accordance with their terms. The net proceeds from the issuance of the 2023 Notes were approximately $364.0 million , after deducting underwriting discounts and commissions and offering expenses payable by the Company. We used approximately $29.4 million of the net proceeds from the issuance of the 2023 Notes to pay the cost of the Capped Call Confirmations described below. The Company intends to use the remainder of the net proceeds for general corporate purposes. Prior to the close of business on the business day immediately preceding April 1, 2023, the 2023 Notes are convertible at the option of the holders only under certain conditions. On or after April 1, 2023, until the close of business on the second scheduled trading day immediately preceding the maturity date, holders may convert their 2023 Notes at their option at the conversion rate then in effect, irrespective of these conditions. The Company may settle conversions of the 2023 Notes by paying or delivering, as the case may be, cash, shares of the Company’s Class C capital stock, or a combination of cash and shares of Class C capital stock, at its election. The conversion rate will initially be 12.7592 shares of Class C capital stock per $1,000 principal amount of 2023 Notes (equivalent to an initial conversion price of approximately $78.37 per share of Class C capital stock). The conversion rate is subject to customary adjustments upon the occurrence of certain events. The Company may redeem for cash all or part of the 2023 Notes, at its option, on or after July 6, 2021, under certain circumstances at a redemption price equal to 100% of the principal amount of the 2023 Notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date (as defined in the indenture governing the 2023 Notes). The conversion option does not meet the criteria for separate accounting as a derivative as it is indexed to our own stock. If the Company undergoes a fundamental change (as defined in the indenture governing the 2023 Notes), holders may require the Company to repurchase for cash all or part of their 2023 Notes at a repurchase price equal to 100% of the principal amount of the 2023 Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date (as defined in the indenture governing the 2023 Notes). In addition, if certain fundamental changes occur, the Company may be required in certain circumstances to increase the conversion rate for any Notes converted in connection with such fundamental changes by a specified number of shares of its Class C capital stock. Certain events are also considered “Events of Default,” which may result in the acceleration of the maturity of the 2023 Notes, as described in the indenture governing the 2023 Notes. There are no financial covenants associated with the 2023 Notes. We may not redeem the 2023 Notes prior to July 6, 2021. We may redeem for cash all or any portion of the 2023 Notes, at our option, in whole or in part on or after July 6, 2021 if the last reported sale price per share of our Class C capital stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading day period. In accounting for the issuance of the 2023 Notes, the Company separated the 2023 Notes into liability and equity components. The carrying amount of the liability component was calculated by measuring the fair value of a similar liability that does not have an associated convertible feature. The carrying amount of the equity component, representing the conversion option, was determined by deducting the fair value of the liability component from the par value of the 2023 Notes. The difference between the principal amount of the 2023 Notes and the liability component represents the debt discount, which is recorded as a direct deduction from the related debt liability in the consolidated balance sheet and amortized to interest expense using the effective interest method over the term of the 2023 Notes. The equity component of the 2023 Notes of approximately $78.6 million is included in additional paid-in capital in the consolidated balance sheet and is not remeasured as long as it continues to meet the conditions for equity classification. Interest expense related to the 2023 Notes for the year ended December 31, 2018 was $10.1 million , which is comprised of approximately $7.3 million related to the amortization of debt discount and debt issuance costs and $2.8 million for the contractual coupon interest. The effective interest rate on the liability component of the 2023 Notes for the year ended December 31, 2018 is 6.99% . Accrued interest related to the 2023 Notes as of December 31, 2018 was not material. Accrued interest is recorded in accrued expenses and other current liabilities in our consolidated balance sheet. The following table presents the outstanding principal amount and carrying value of the 2023 Notes as of the date presented (in thousands): Outstanding Principal Amount Unamortized Debt Discount and Debt Issuance Costs Carrying Value December 31, 2018 $ 373,750 $ (79,012 ) $ 294,738 As of December 31, 2018 , the unamortized debt discount and debt issuance costs for the 2023 Notes will be amortized to interest expense over a remaining period of approximately 54 months . The estimated fair value of the 2023 Notes was $321.9 million as of December 31, 2018 . The estimated fair value of the 2023 Notes was determined through consideration of quoted market prices. The fair value is classified as Level 3 due to the limited trading activity for the 2023 Notes. The Capped Call Confirmations are expected generally to reduce the potential dilution of our Class C capital stock upon any conversion of 2023 Notes and/or offset the cash payments the Company is required to make in excess of the principal amount of the 2023 Notes in the event that the market price of the Class C capital stock is greater than the strike price of the Capped Call Confirmations (which initially corresponds to the initial conversion price of the 2023 Notes and is subject to certain adjustments under the terms of the Capped Call Confirmations), with such reduction and/or offset subject to a cap based on the cap price of the Capped Call Confirmations. The Capped Call Confirmations have an initial cap price of $105.45 per share, which represents a premium of approximately 85% over the public offering price of the Company’s Class C capital stock in the concurrent share offering of $57.00 , and is subject to certain adjustments under the terms of the Capped Call Confirmations. The Capped Call Confirmations will cover, subject to anti-dilution adjustments substantially similar to the 2023 Notes, the number of shares of Class C capital stock that will underlie the 2023 Notes. The Capped Call Confirmations do not meet the criteria for separate accounting as a derivative as they are indexed to our own stock. The premiums paid for the Capped Call Confirmations have been included as a net reduction to additional paid-in-capital within shareholders’ equity. Convertible Senior Notes due in 2021 On December 12, 2016, Zillow Group issued $460.0 million aggregate principal amount of 2.00% Convertible Senior Notes due 2021 (the “2021 Notes”), which amount includes the exercise in full of the $60.0 million over-allotment option, to Citigroup Global Markets Inc. as the initial purchaser of the 2021 Notes in a private offering to the initial purchaser in reliance on the exemption from the registration requirements provided by Section 4(a)(2) of the Securities Act of 1933, as amended (the “Securities Act”) for resale to qualified institutional buyers as defined in, and pursuant to, Rule 144A under the Securities Act. The 2021 Notes bear interest at a fixed rate of 2.00% per year, payable semi-annually in arrears on June 1 and December 1 of each year. The 2021 Notes are convertible into cash, shares of our Class C capital stock or a combination thereof, at the Company’s election. The 2021 Notes will mature on December 1, 2021, unless earlier repurchased, redeemed, or converted in accordance with their terms. The net proceeds from the issuance of the 2021 Notes were approximately $447.8 million , after deducting fees and expenses. The Company used approximately $370.2 million of the net proceeds from the issuance of the 2021 Notes to repurchase a portion of the outstanding 2020 Notes (see additional information below under “Trulia’s Convertible Senior Notes due 2020”) in privately negotiated transactions. In addition, the Company used approximately $36.6 million of the net proceeds from the issuance of the 2021 Notes to pay the cost of the capped call transactions with the initial purchaser of the 2021 Notes and two additional financial institutions (“Capped Call Confirmations”) as discussed further below. The Company used the remainder of the net proceeds for general corporate purposes. Prior to the close of business on the business day immediately preceding September 1, 2021, the 2021 Notes are convertible at the option of the holders of the 2021 Notes only under certain conditions, none of which conditions have been satisfied as of December 31, 2018 . On or after September 1, 2021, until the close of business on the second scheduled trading day immediately preceding the maturity date, holders of the 2021 Notes may convert their 2021 Notes at their option at the conversion rate then in effect, irrespective of these conditions. The Company may settle conversions of the 2021 Notes by paying or delivering, as the case may be, cash, shares of Class C capital stock, or a combination of cash and shares of Class C capital stock, at its election. The conversion rate will initially be 19.0985 shares of Class C capital stock per $1,000 principal amount of 2021 Notes (equivalent to an initial conversion price of approximately $52.36 per share of Class C capital stock). The conversion rate is subject to customary adjustments upon the occurrence of certain events. The Company may redeem for cash all or part of the 2021 Notes, at its option, on or after December 6, 2019, under certain circumstances at a redemption price equal to 100% of the principal amount of the 2021 Notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date (as defined in the indenture governing the 2021 Notes). The conversion option does not meet the criteria for separate accounting as a derivative as it is indexed to our own stock. If the Company undergoes a fundamental change (as defined in the indenture governing the 2021 Notes), holders of the 2021 Notes may require the Company to repurchase for cash all or part of their 2021 Notes at a repurchase price equal to 100% of the principal amount of the 2021 Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date (as defined in the indenture governing the 2021 Notes). In addition, if certain fundamental changes occur, the Company may be required in certain circumstances to increase the conversion rate for any 2021 Notes converted in connection with such fundamental changes by a specified number of shares of its Class C capital stock. Certain events are also considered “Events of Default,” which may result in the acceleration of the maturity of the 2021 Notes, as described in the indenture governing the notes. There are no financial covenants associated with the 2021 Notes. We may not redeem the 2021 Notes prior to December 6, 2019. We may redeem the 2021 Notes for cash, at our option, in whole or in part on or after December 6, 2019, if the last reported sale price per share of our Class C capital stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading day period. In accounting for the issuance of the 2021 Notes, the Company separated the 2021 Notes into liability and equity components. The carrying amount of the liability component was calculated by measuring the fair value of a similar liability that does not have an associated conversion feature. The carrying amount of the equity component, representing the conversion option, was determined by deducting the fair value of the liability component from the par value of the 2021 Notes. The difference between the principal amount of the 2021 Notes and the liability component represents the debt discount, which is recorded as a direct deduction from the related debt liability in the consolidated balance sheet and amortized to interest expense using the effective interest method over the term of the 2021 Notes. The equity component of the 2021 Notes of approximately $91.4 million is included in additional paid-in capital in the consolidated balance sheet and is not remeasured as long as it continues to meet the conditions for equity classification. The Company incurred transaction costs of approximately $12.2 million related to the issuance of the 2021 Notes, including approximately $11.5 million in fees to the initial purchaser, which amount was paid out of the gross proceeds from the note offering. In accounting for the transaction costs, the Company allocated the total amount incurred to the liability and equity components using the same proportions as the proceeds from the 2021 Notes. Transaction costs attributable to the liability component were recorded as a direct deduction from the related debt liability in the consolidated balance sheet and amortized to interest expense over the term of the 2021 Notes, and transaction costs attributable to the equity component were netted with the equity component in shareholders’ equity. Interest expense related to the 2021 Notes for the year ended December 31, 2018 was $28.6 million , which is comprised of approximately $19.4 million related to the amortization of debt discount and debt issuance costs and $9.2 million for the contractual coupon interest. Interest expense related to the 2021 Notes for the year ended December 31, 2017 was $27.2 million , which is comprised of approximately $18.0 million related to the amortization of debt discount and debt issuance costs and $9.2 million for the contractual coupon interest. Interest expense related to the 2021 Notes for the year ended December 31, 2016 was $1.3 million , which is comprised of approximately $0.9 million related to the amortization of debt discount and debt issuance costs and $0.5 million for the contractual coupon interest. The effective interest rate on the liability component of the 2021 Notes is 7.44% for the years ended December 31, 2018 , 2017 and 2016 . Accrued interest related to the 2021 Notes was $0.8 million as of December 31, 2018 and 2017 and is recorded in accrued expenses and other current liabilities in the consolidated balance sheet. The following table presents the outstanding principal amount and carrying value of the 2021 Notes as of the dates presented (in thousands): Outstanding Principal Amount Unamortized Debt Discount and Debt Issuance Costs Carrying Value December 31, 2018 $ 460,000 $ (65,355 ) $ 394,645 December 31, 2017 $ 460,000 $ (84,721 ) $ 375,279 As of December 31, 2018 , the unamortized debt discount and debt issuance costs for the 2021 Notes will be amortized to interest expense over a remaining period of approximately 35 months . The estimated fair value of the 2021 Notes was $446.2 million and $509.0 million , respectively, as of December 31, 2018 and 2017. The estimated fair value of the 2021 Notes was determined through consideration of quoted market prices. The fair value is classified as Level 3 due to the limited trading activity for the 2021 Notes. The Capped Call Confirmations are expected generally to reduce the potential dilution of our Class C capital stock upon any conversion of 2021 Notes and/or offset the cash payments the Company is required to make in excess of the principal amount of the 2021 Notes in the event that the market price of the Class C capital stock is greater than the strike price of the Capped Call Confirmations (which initially corresponds to the initial conversion price of the 2021 Notes and is subject to certain adjustments under the terms of the Capped Call Confirmations), with such reduction and/or offset subject to a cap based on the cap price of the Capped Call Confirmations. The Capped Call Confirmations have an initial cap price of $69.19 per share, which represents a premium of approximately 85% over the closing price of the Company’s Class C capital stock on The Nasdaq Global Select Market on December 6, 2016, and is subject to certain adjustments under the terms of the Capped Call Confirmations. The Capped Call Confirmations will cover, subject to anti-dilution adjustments substantially similar to those applicable to the 2021 Notes, the number of shares of Class C capital stock that will underlie the 2021 Notes. In addition, the Capped Call Confirmations provide for the Company to elect, subject to certain conditions, for the Capped Call Confirmations to remain outstanding (with certain modifications) following its election to redeem the 2021 Notes, notwithstanding any conversions of 2021 Notes in connection with such redemption. The Capped Call Confirmations do not meet the criteria for separate accounting as a derivative as they are indexed to our own stock. The premiums paid for the Capped Call Confirmations have been included as a net reduction to additional paid-in capital within shareholders’ equity. Trulia’s Convertible Senior Notes due in 2020 In connection with the February 2015 acquisition of Trulia, a portion of the total purchase price was allocated to Trulia’s Convertible Senior Notes due in 2020 (the “2020 Notes”), which are unsecured senior obligations. Pursuant to and in accordance with the Merger Agreement, Zillow Group entered into a supplemental indenture in respect of the 2020 Notes in the aggregate principal amount of $230.0 million , which supplemental indenture provides, among other things, that, at the effective time of the Trulia Merger, (i) each outstanding 2020 Note is no longer convertible into shares of Trulia common stock and is convertible solely into shares of Zillow Group Class A common stock, pursuant to, and in accordance with, the terms of the indenture governing the 2020 Notes, and (ii) Zillow Group guaranteed all of the obligations of Trulia under the 2020 Notes and related indenture. In December 2016, the Company used approximately $370.2 million of the net proceeds from the issuance of the 2021 Notes discussed above to repurchase $219.9 million aggregate principal of the 2020 Notes in privately negotiated transactions. The aggregate principal amount of the 2020 Notes is due on December 15, 2020 if not earlier converted or redeemed. Interest is payable on the 2020 Notes at the rate of 2.75% semi-annually on June 15 and December 15 of each year. Holders of the 2020 Notes may convert all or any portion of their notes, in multiples of $1,000 principal amount, at their option at any time prior to the close of business on the business day immediately preceding the maturity date. Regarding the supplemental indenture in respect of the 2020 Notes, the conversion ratio immediately prior to the effective time of the Trulia Merger of 27.8303 shares of Trulia common stock per $1,000 principal amount of notes was adjusted to 12.3567 shares of our Class A common stock per $1,000 principal amount of notes based on the exchange ratio of 0.444 per the Merger Agreement. This was equivalent to an initial conversion price of approximately $80.93 per share of our Class A common stock. Regarding the August 2015 distribution of shares of our Class C capital stock as a dividend to our Class A and Class B common shareholders, the conversion ratio has been further adjusted to 41.4550 shares of Class A common stock per $1,000 principal amount of notes, which is equivalent to a conversion price of approximately $24.12 per share of our Class A common stock. The conversion ratio will be adjusted for certain dilutive events and will be increased in the case of corporate events that constitute a “Make-Whole Fundamental Change” (as defined in the indenture governing the notes). The conversion option of the 2020 Notes has no cash settlement provisions. The conversion option does not meet the criteria for separate accounting as a derivative as it is indexed to our own stock. The holders of the 2020 Notes will have the ability to require us to repurchase the notes in whole or in part upon the occurrence of an event that constitutes a “Fundamental Change” (as defined in the indenture governing the notes, including such events as a “change in control” or “termination of trading”, subject to certain exceptions). In such case, the repurchase price would be 100% of the principal amount of the 2020 Notes plus accrued and unpaid interest, if any, to, but excluding, the Fundamental Change repurchase date. Certain events are also considered “Events of Default,” which may result in the acceleration of the maturity of the 2020 Notes, as described in the indenture governing the notes. There are no financial covenants associated with the 2020 Notes. The 2020 Notes are redeemable, at our option, in whole or in part as of December 20, 2018, if the last reported sale price per share of our Class A common stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading day period. Interest expense related to the 2020 Notes for the years ended December 31, 2018 and 2017 was $0.3 million , and for the year ended December 31, 2016 was $6.1 million . Accrued interest related to the 2020 Notes as of December 31, 2018 and 2017 was not material. Accrued interest is recorded in accrued expenses and other current liabilities in our consolidated balance sheet. The carrying value of the 2020 Notes was $9.6 million and $10.1 million , respectively, as of December 31, 2018 and 2017 . The estimated fair value of the 2020 Notes was $16.7 million and $17.6 million , respectively, as of December 31, 2018 and 2017

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes We are subject to federal and state income taxes in the United States and in Canada. For the years ended December 31, 2018 , 2017 and 2016 , we did not have a material amount of current taxable income. We recorded an income tax benefit of $31.1 million for the year ended December 31, 2018 . Approximately $15.4 million of the income tax benefit relates to a $69.0 million non-cash impairment we recorded during the year ended December 31, 2018 related to the indefinite-lived Trulia trade names and trademarks intangible asset. The remaining portion of our income tax benefit is primarily the result of net operating losses generated after December 31, 2017 with an indefinite carryforward period due to the Tax Act. Current year net operating losses can now offset against the indefinite-lived deferred tax liabilities which resulted in a release of the valuation allowance and a resulting income tax benefit. During the year ended December 31, 2018 , we completed our accounting for the income tax effects related to the deduction limitations on compensation under the Tax Act. The Internal Revenue Service provided further guidance in applying the written binding contracts requirement under the Tax Act, and we believe certain of our executive compensation previously eligible to be deductible for tax purposes under Section 162(m) of the Internal Revenue Code will be considered grandfathered and, therefore, will continue to be deductible. Based on the clarification of these rules, the accounting related to the Section 162(m) limitation of the Internal Revenue Code is considered complete and as a result we recorded a $5.9 million tax benefit for the year ended December 31, 2018 . We recorded an income tax benefit of $89.6 million for the year ended December 31, 2017. Approximately $66.0 million of the income tax benefit relates to a $174.0 million non-cash impairment we recorded during the year ended December 31, 2017 related to the $351.0 million indefinite-lived intangible asset that we recorded in connection with our February 2015 acquisition of Trulia for Trulia’s trade names and trademarks. For additional information about the non-cash impairment, see Note 11 to our consolidated financial statements. The remaining $23.6 million of the income tax benefit primarily relates to our initial analysis of the impact of the rate decrease included in the Tax Act for the impact of the reduction in our net deferred tax liability related to our indefinite-lived intangible asset. The following table summarizes the components of our income tax (benefit) expense for the periods presented (in thousands): Year Ended December 31, 2018 2017 2016 Current income tax expense Foreign $ 161 $ — $ — Total current income tax expense 161 — — Deferred income tax (benefit) expense Federal (28,502 ) (84,238 ) (1,248 ) State (2,441 ) (5,348 ) 1,378 Foreign (320 ) — — Total deferred income tax (benefit) expense (31,263 ) (89,586 ) 130 Total income tax (benefit) expense $ (31,102 ) $ (89,586 ) $ 130 The following table presents a reconciliation of the federal statutory rate and our effective tax rate for the periods presented: Year Ended December 31, 2018 2017 2016 Tax expense at federal statutory rate (21.0 )% (35.0 )% (35.0 )% State income taxes, net of federal tax benefit (5.9 ) (4.4 ) (1.9 ) Nondeductible expenses — 0.8 4.9 Share-based compensation (16.5 ) (20.6 ) (0.2 ) IRC section 162(m) 1.0 — — Research and development credits (8.4 ) (6.3 ) (1.5 ) Meals and entertainment 1.8 — — Return to provision adjustments (4.2 ) — — Enactment of Tax Act (1.9 ) (13.1 ) — Other 0.4 2.2 (0.9 ) Valuation allowance 34.0 27.7 34.7 Effective tax rate (20.7 )% (48.7 )% 0.1 % Deferred federal, state and foreign income taxes reflect the net tax impact of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and such amounts for tax purposes. The following table presents the significant components of our deferred tax assets and liabilities as of the dates presented (in thousands): December 31, 2018 2017 Deferred tax assets: Federal and state net operating loss carryforwards $ 259,629 $ 234,316 Share-based compensation 55,280 47,655 Start-up and organizational costs 99 146 Research and development credits 48,805 35,793 Other tax credits 910 910 Accruals and reserves 3,000 2,729 Deferred rent 4,842 5,484 Other deferred tax assets 14,267 8,342 Total deferred tax assets 386,832 335,375 Deferred tax liabilities: Website and software development costs (14,685 ) (13,202 ) Goodwill (598 ) (688 ) Intangible assets (45,035 ) (69,241 ) Discount on 2021 Notes and 2023 Notes not deductible for tax (31,450 ) (19,374 ) Depreciation and amortization (888 ) (2,425 ) Total deferred tax liabilities (92,656 ) (104,930 ) Net deferred tax assets before valuation allowance 294,176 230,445 Less: valuation allowance (307,599 ) (274,810 ) Net deferred tax liabilities $ (13,423 ) $ (44,365 ) Realization of deferred tax assets is dependent upon the generation of future taxable income, if any, the timing and amount of which are uncertain. We have provided a full valuation allowance against the net deferred tax assets as of December 31, 2018 and 2017 because, based on the weight of available evidence, it is more likely than not (a likelihood of more than 50%) that some or all of the deferred tax assets will not be realized. The valuation allowance increased by $32.8 million and $57.5 million , respectively, during the years ended December 31, 2018 and 2017 . We have accumulated federal tax losses of approximately $1,081.7 million and $1,014.0 million , respectively, as of December 31, 2018 and 2017 , which are available to reduce future taxable income. We have accumulated state tax losses of approximately $32.5 million and $21.4 million (tax effected), respectively, as of December 31, 2018 and 2017 . Additionally, we have net research and development credit carryforwards of $48.8 million and $35.8 million , respectively, as of December 31, 2018 and 2017 , which are available to reduce future tax liabilities. The tax loss and research and development credit carryforwards begin to expire in 2025 . Under Sections 382 and 383 of the Internal Revenue Code, if a corporation undergoes an ownership change, the corporation’s ability to use its pre-change net operating loss carryforwards and other pre-change tax attributes, such as research tax credits, to offset its post-change income or income tax liability may be limited. In connection with our August 2013 public offering of our Class A Common stock, we experienced an ownership change that triggered Sections 382 and 383, which may limit our ability to utilize net operating loss and tax credit carryforwards. In connection with our February 2015 acquisition of Trulia, Trulia experienced an ownership change that triggered Section 382 and 383, which may limit Zillow Group’s ability to utilize Trulia’s net operating loss and tax credit carryforwards. We are currently not under audit in any tax jurisdiction. Tax years from 2015 through 2018 are currently open for audit by federal and state taxing authorities. Changes for unrecognized tax benefits for the periods presented are as follows (in thousands): Balance at January 1, 2016 $ 13,980 Gross increases—prior and current period tax positions 2,619 Gross decreases—prior period tax positions (1,204 ) Balance at December 31, 2016 $ 15,395 Gross increases—current period tax positions 5,216 Gross increases—prior period tax positions 1,002 Balance at December 31, 2017 $ 21,613 Gross increases—current period tax positions 6,421 Gross increases—prior period tax positions 591 Balance at December 31, 2018 $ 28,625 At December 31, 2018 , the total amount of unrecognized tax benefits of $28.6 million is recorded as a reduction to our deferred tax asset. We do not anticipate that the amount of existing unrecognized tax benefits will significantly increase or decrease within the next 12 months. Accrued interest and penalties related to unrecognized tax benefits are recorded as income tax expense and are zero

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Shareholders' Equity	Shareholders’ Equity Preferred Stock Our board of directors has the authority to fix and determine and to amend the number of shares of any series of preferred stock that is wholly unissued or to be established and to fix and determine and to amend the designation, preferences, voting powers and limitations, and the relative, participating, optional or other rights, of any series of shares of preferred stock that is wholly unissued or to be established, subject in each case to certain approval rights of holders of our outstanding Class B common stock. There was no preferred stock issued and outstanding as of December 31, 2018 or December 31, 2017 . Common and Capital Stock 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 into Class A common stock upon the affirmative vote by or written consent of holders of a majority of the shares of the Class B common stock. During the years ended December 31, 2018 , 2017 and 2016 , no 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. Our Class C capital stock has no preferences or privileges, is not redeemable and, except in limited circumstances, is no n-voting. On July 3, 2018, Zillow Group issued and sold 6,557,017 shares (of which 855,263 shares were related to the exercise of the underwriters’ option to purchase additional shares) of our Class C capital stock at a public offering price of $57.00 per share. We received net proceeds of $360.3 million after deducting underwriting discounts and commissions and offering expenses payable by us. The following shares of common and capital stock have been reserved for future issuance as of the dates presented: December 31, 2018 December 31, 2017 Option awards outstanding 27,310,110 26,645,206 Restricted stock units outstanding 5,266,324 4,016,405 Class A common stock and Class C capital stock available for grant under 2011 Plan 3,675,082 5,076,898 Shares issuable upon conversion of outstanding Class B common stock 6,217,447 6,217,447 Total 42,468,963 41,955,956

Share-Based Awards

Share-Based Awards	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Awards	Share-Based Awards In connection with our February 2015 acquisition of Trulia, we assumed the obligations of Zillow and Trulia outstanding under pre-existing stock plans. We intend that future equity grants will be made under Zillow Group’s 2011 Amended and Restated Incentive Plan (as amended and/or restated from time to time, the “2011 Plan”) only (or a successor thereto). Zillow Group, Inc. Amended and Restated 2011 Incentive Plan On July 19, 2011, the 2011 Plan became effective. In addition to the share reserve of 18,400,000 shares, the number of shares available for issuance under the 2011 Plan automatically increases on the first day of each of our fiscal years by a number of shares equal to the least of (a) 3.5% of our outstanding Class A common stock, Class B common stock, and Class C capital stock on a fully diluted basis as of the end of our immediately preceding fiscal year, (b) 10,500,000 shares, and (c) a lesser amount determined by our board of directors; provided, however, that any shares from any increases in previous years that are not actually issued will continue to be available for issuance under the 2011 Plan. In addition, shares previously available for grant under Zillow, Inc.’s 2005 Equity Incentive Plan (the “2005 Plan”), but not issued or subject to outstanding awards under the 2005 Plan as of July 19, 2011, and shares subject to outstanding awards under the 2005 Plan that subsequently cease to be subject to such awards (other than by reason of exercise of the awards) are available for grant under the 2011 Plan. The 2011 Plan is administered by the compensation committee of the board of directors. Under the terms of the 2011 Plan, the compensation committee may grant equity awards, including incentive stock options, nonqualified stock options, restricted stock, restricted stock units or restricted units to employees, officers, directors, consultants, agents, advisers and independent contractors. The board of directors has also authorized certain senior executive officers to grant equity awards under the 2011 Plan, within limits prescribed by our board of directors. The 2011 Plan provides that in the event of a stock dividend, stock split or similar event, the maximum number and kind of securities available for issuance under the plan will be proportionally adjusted. Options under the 2011 Plan are granted with an exercise price per share not less than 100% of the fair market value of our stock on the date of grant, with the exception of substituted option awards granted in connection with acquisitions, and are exercisable at such times and under such conditions as determined by the compensation committee. 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 3 months following their termination of employment or 12 months following termination by reason of death, disability or retirement. Options granted under the 2011 Plan typically expire seven or ten years from the grant date and typically vest either 25% after 12 months and ratably thereafter over the next 36 months or quarterly over a period of four years , though certain options have been granted with alternative vesting schedules. Restricted stock units granted under the 2011 Plan typically vest either 25% after 12 months and quarterly thereafter over the next three years , quarterly over a period of four years , or 12.5% after 6 months and quarterly thereafter for the next 3.5 years . Any portion of a restricted stock unit that is not vested on the date of a participant’s termination of service expires on such date. In March 2016, Zillow Group established an equity choice program pursuant to which Zillow Group grants restricted stock units and option awards to acquire shares of Class C capital stock to certain employees to retain and recognize their efforts on behalf of Zillow Group. Trulia 2005 Stock Incentive Plan Trulia granted options under its 2005 Stock Incentive Plan (as amended, “the 2005 Plan”) until September 2012 when the 2005 Plan was terminated. Stock options issued prior to the plan termination remained outstanding in accordance with their terms. Under the terms of the 2005 Plan, Trulia had the ability to grant incentive and nonqualified stock options, stock appreciation rights, restricted stock awards and restricted stock units. Options granted under the 2005 Plan generally vest at a rate of 25% after 12 months and ratably thereafter over the next 36 months and expire 10 years from the grant date. Certain options vest monthly over two to four years . Trulia 2012 Equity Incentive Plan, as Amended and Restated On September 19, 2012, Trulia’s 2012 Equity Incentive Plan (the “2012 Plan”) became effective. The 2012 Plan provides for the grant of incentive and nonqualified stock options, restricted stock, restricted stock units, stock appreciation rights, performance units and performance shares to employees, directors and consultants. Under the 2012 Plan, stock options are granted at a price per share not less than 100% of the fair market value per share of the underlying stock at the grant date. The plan administrator determines the vesting period for each option award on the grant date, and the options generally expire 10 years from the grant date or such shorter term as may be determined for the options. As noted above, we intend that future equity grants will be made under the 2011 Plan only. Option Awards The following table summarizes option award activity for the year ended December 31, 2018 : Number of Shares Subject to Existing Options Weighted- Average Exercise Price Per Share Weighted- Average Remaining Contractual Life (Years) Aggregate Intrinsic Value (in thousands) Outstanding at January 1, 2018 26,645,206 $ 27.70 5.72 $ 355,739 Granted 6,963,320 48.95 Exercised (5,472,728 ) 21.94 Forfeited or cancelled (825,688 ) 35.32 Outstanding at December 31, 2018 27,310,110 34.04 6.23 97,941 Vested and exercisable at December 31, 2018 15,287,932 29.73 4.72 75,867 The fair value of options granted is estimated at the date of grant using the Black-Scholes-Merton option-pricing model, assuming no dividends and with the following assumptions for the periods presented: Year Ended December 31, 2018 2017 2016 Expected volatility 42% – 45% 45% – 49% 49% – 51% Expected dividend yield — — — Risk-free interest rate 2.52% – 2.84% 1.67% – 2.06% 0.89% – 1.89% Weighted-average expected life 4.50 – 5.00 years 4.25 – 4.75 years 3.75 – 4.25 years Weighted-average fair value of options granted $19.11 $14.51 $9.42 As of December 31, 2018 , there was a total of $176.7 million in unrecognized compensation cost related to unvested stock options, which is expected to be recognized over a weighted-average period of 2.7 years . The total intrinsic value of options exercised during the years ended December 31, 2018 , 2017 and 2016 was $161.4 million , $156.1 million and $51.7 million , respectively. The fair value of options vested for the years ended December 31, 2018 , 2017 and 2016 was $87.7 million , $84.8 million and $87.9 million , respectively. Restricted Stock Units The following table summarizes activity for restricted stock units for the year ended December 31, 2018 : Restricted Stock Units Weighted- Average Grant- Date Fair Value Unvested outstanding at January 1, 2018 4,016,405 $ 33.22 Granted 3,725,726 48.26 Vested (1,740,134 ) 35.63 Forfeited or cancelled (735,673 ) 39.59 Unvested outstanding at December 31, 2018 5,266,324 42.19 The total fair value of vested restricted stock units was $62.0 million , $43.7 million and $46.5 million , respectively, for the years ended December 31, 2018 , 2017 and 2016 . The fair value of the outstanding restricted stock units will be recorded as share-based compensation expense over the vesting period. As of December 31, 2018 , there was $204.9 million of total unrecognized compensation cost related to restricted stock units, which is expected to be recognized over a weighted-average period of 2.9 years . Share-Based Compensation Expense The following table presents the effects of share-based compensation expense in our consolidated statements of operations during the periods presented (in thousands): Year Ended December 31, 2018 2017 2016 Cost of revenue $ 4,127 $ 3,884 $ 3,550 Sales and marketing 22,942 22,735 23,320 Technology and development 56,673 39,938 31,466 General and administrative 65,342 47,014 48,582 $ 149,084 $ 113,571 $ 106,918

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Net Loss Per Share	Net Loss Per Share Basic net loss per share is computed by dividing net loss by the weighted-average number of shares (including Class A common stock, Class B common stock and Class C capital stock) outstanding during the period. In the calculation of basic net loss per share, undistributed earnings are allocated assuming all earnings during the period were distributed. Diluted net loss per share is computed by dividing net loss by the weighted-average number of shares (including Class A common stock, Class B common stock and Class C capital stock) outstanding during the period and potentially dilutive Class A common stock and Class C capital stock equivalents, except in cases where the effect of the Class A common stock or Class C capital stock equivalent would be antidilutive. Potential Class A common stock and Class C capital stock equivalents consist of Class A common stock and Class C capital stock issuable upon exercise of stock options and Class A common stock and Class C capital stock underlying unvested restricted stock awards and unvested restricted stock units using the treasury stock method. Potential Class A common stock equivalents also include Class A common stock issuable upon conversion of the 2020 Notes using the if-converted method. Since the Company expects to settle the principal amount of the outstanding 2021 Notes and 2023 Notes in cash, the Company uses the treasury stock method for calculating any potential dilutive effect of the conversion spread on diluted net income per share, if applicable. For the 2021 Notes, the conversion spread of approximately 8.8 million shares has a dilutive impact on diluted net income per share when the market price of the Company’s Class C capital stock at the end of a period exceeds the conversion price of $52.36 per share. For the 2023 Notes, the conversion spread of approximately 4.8 million shares has a dilutive impact on diluted net income per share when the market price of the Company’s Class C capital stock at the end of a period exceeds the conversion price of $78.37 per share. For the periods presented, the following Class A common stock and Class C capital stock equivalents were excluded from the calculations of diluted net loss per share because their effect would have been antidilutive (in thousands): Year Ended December 31, 2018 2017 2016 Weighted-average Class A common stock and Class C capital stock option awards outstanding 22,736 27,998 19,993 Weighted-average Class A common stock and Class C capital stock restricted stock units outstanding 4,949 4,262 3,607 Class A common stock issuable upon conversion of the 2020 Notes 400 435 440 Total Class A common stock and Class C capital stock equivalents 28,085 32,695 24,040

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Lease Commitments We have contractual obligations in the form of operating leases for office space and office equipment. The largest of these leases relates to our headquarters in Seattle, Washington, as well as our other offices in San Francisco, California, Denver, Colorado, Overland Park, Kansas, Irvine, California and New York, New York. Each of these leases contain periodic rent escalation adjustments and renewal options. Rent expense related to these leases is recorded on a straight-line basis. Our operating lease obligations expire at various dates with the latest maturity in 2024. Future minimum payments for all operating leases as of December 31, 2018 are as follows (in thousands): 2019 $ 29,085 2020 38,060 2021 40,099 2022 37,721 2023 36,458 All future years 85,462 Total future minimum lease payments $ 266,885 Rent expense for the years ended December 31, 2018 , 2017 and 2016 , was $23.7 million , $21.4 million and $16.6 million , respectively. Purchase Commitments Purchase commitments primarily included non-cancelable agreements to purchase content related to our mobile applications and websites as well as homes that the Company is under contract to purchase through Zillow Offers but that have not closed as of the respective date. The amounts due for these non-cancelable purchase commitments and homes under contract as of December 31, 2018 are as follows (in thousands): Purchase Obligations Homes Under Contract 2019 $ 64,124 $ 88,943 2020 64,007 — 2021 32,735 — Total future purchase commitments $ 160,866 $ 88,943 Surety Bonds In the course of business, we are required to provide financial commitments in the form of surety bonds to third parties as a guarantee of our performance on and our compliance with certain obligations. If we were to fail to perform or comply with these obligations, any draws upon surety bonds issued on our behalf would then trigger our payment obligation to the surety bond issuer. We have outstanding surety bonds issued for our benefit of approximately $8.9 million and $3.7 million as of December 31, 2018 and 2017 , respectively. Legal Proceedings We are involved in a number of legal proceedings concerning matters arising in connection with the conduct of our business activities, some of which are at preliminary stages and some of which seek an indeterminate amount of damages. We regularly evaluate the status of legal proceedings in which we are involved to assess whether a loss is probable or there is a reasonable possibility that a loss or additional loss may have been incurred to determine if accruals are appropriate. We further evaluate each legal proceeding to assess whether an estimate of possible loss or range of loss can be made if accruals are not appropriate. For certain cases described below, management is unable to provide a meaningful estimate of the possible loss or range of possible loss because, among other reasons, (i) the proceedings are in preliminary stages; (ii) specific damages have not been sought; (iii) damages sought are, in our view, unsupported and/or exaggerated; (iv) there is uncertainty as to the outcome of pending appeals or motions; (v) there are significant factual issues to be resolved; and/or (vi) there are novel legal issues or unsettled legal theories presented. For these cases, however, management does not believe, based on currently available information, that the outcomes of these proceedings will have a material effect on our financial position, results of operations or cash flow. In July 2015, VHT, Inc. (“VHT”) filed a complaint against us in the U.S. District Court for the Western District of Washington alleging copyright infringement of VHT’s images on the Zillow Digs site. In January 2016, VHT filed an amended complaint alleging copyright infringement of VHT’s images on the Zillow Digs site as well as the Zillow listing site. In December 2016, the court granted a motion for partial summary judgment that dismissed VHT’s claims with respect to the Zillow listing site. A federal jury trial began on January 23, 2017, and on February 9, 2017, the jury returned a verdict finding that the Company had infringed VHT’s copyrights in images displayed or saved to the Digs site. The jury awarded VHT $79,875 in actual damages and approximately $8.2 million in statutory damages. In March 2017, the Company filed motions in the district court seeking judgment for the Company on certain claims that are the subject of the verdict, and for a new trial on others. On June 20, 2017, the judge ruled and granted in part our motions, finding that VHT failed to present sufficient evidence to prove direct copyright infringement for a portion of the images, reducing the total damages to approximately $4.1 million . On October 26, 2017, the Company filed an appeal with the Ninth Circuit Court of Appeals seeking review of the final judgment and certain prior rulings entered by the district court. The oral hearing for the appeal took place on August 28, 2018. We have recorded an estimated liability for approximately $4.1 million as of December 31, 2018 and December 31, 2017 . We do not believe there is a reasonable possibility that a material loss in excess of amounts accrued may be incurred. In August and September 2017, two purported class action lawsuits were filed against us and certain of our executive officers, alleging, among other things, violations of federal securities laws on behalf of a class of those who purchased our common stock between February 12, 2016 and August 8, 2017. One of those purported class actions, captioned Vargosko v. Zillow Group, Inc. et al, was brought in the U.S. District Court for the Central District of California. The other purported class action lawsuit, captioned Shotwell v. Zillow Group, Inc. et al, was brought in the U.S. District Court for the Western District of Washington. The complaints allege, among other things, that during the period between February 12, 2016 and August 8, 2017, we issued materially false and misleading statements regarding our business practices. The complaints seek to recover, among other things, alleged damages sustained by the purported class members as a result of the alleged misconduct. In November 2017, an amended complaint was filed against us and certain of our executive officers in the Shotwell v. Zillow Group class action lawsuit, extending the beginning of the class period to November 17, 2014. In January 2018, the Vargosko v. Zillow Group class action lawsuit was transferred to the U.S. District Court for the Western District of Washington and consolidated with the Shotwell v. Zillow Group class action lawsuit, and the court appointed lead plaintiffs in the consolidated lawsuit. In February 2018, lead plaintiffs filed a consolidated amended complaint, and in April 2018, we filed our motion to dismiss the consolidated amended complaint. Our motion to dismiss the consolidated amended complaint was fully briefed in June 2018. On October 2, 2018, the court granted our motion to dismiss, although the court gave lead plaintiffs 45 days, or until November 16, 2018, to file a second consolidated amended complaint and attempt to cure the defects in their consolidated amended complaint. On November 16, 2018, lead plaintiffs filed a second consolidated amended complaint, which we moved to dismiss on December 17, 2018. We anticipate that briefing on our motion to dismiss the second consolidated amended complaint will be complete by February 6, 2019. We have denied the allegations of wrongdoing and intend to vigorously defend the claims in this lawsuit. We have not recorded an accrual related to this lawsuit as of December 31, 2018 and December 31, 2017 , as we do not believe a loss is probable. In October and November 2017 and January and February 2018, four shareholder derivative lawsuits were filed in the U.S. District Court for the Western District of Washington and the Superior Court of the State of Washington, against certain of our executive officers and directors seeking unspecified damages on behalf of the Company and certain other relief, such as reform to corporate governance practices. The plaintiffs in the derivative lawsuits (in which the Company is a nominal defendant) allege, among other things, that the defendants breached their fiduciary duties in connection with oversight of public statements and legal compliance, and as a result of the breach of such fiduciary duties, the Company was damaged, and defendants were unjustly enriched. Certain of the plaintiffs also allege, among other things, violations of Section 14(a) of the Securities Exchange Act of 1934 and waste of corporate assets. All four of the shareholder derivative lawsuits have been stayed until after final resolution of the pending motion to dismiss and related appeals, if any, in the consolidated securities class action lawsuit discussed above. The defendants intend to deny the allegations of wrongdoing and vigorously defend the claims in these lawsuits. We have not recorded an accrual related to these lawsuits as of December 31, 2018 and December 31, 2017 , as we do not believe a loss is probable. In addition to the matters discussed above, from time to time, we are involved in litigation and claims that arise in the ordinary course of business. Although we cannot be certain of the outcome of any such litigation or 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 business, financial position, results of operations or cash flow. Regardless of the outcome, litigation can have an adverse impact on us because of defense and settlement costs, diversion of management resources and other factors. Indemnifications

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions In February 2016, we paid a total of approximately $0.2 million and $0.2 million , respectively, to Mr. Lloyd Frink, our Vice Chairman and President, and Mr. Richard Barton, our Executive Chairman, for reimbursement of costs incurred by Mr. Frink and Mr. Barton for use of private planes by certain of the Company’s employees and Mr. Frink and Mr. Barton for business travel in prior years. In April 2016, we paid approximately $0.1 million

Self-Insurance

Self-Insurance	12 Months Ended
	Dec. 31, 2018
Insurance [Abstract]
Self-Insurance	Self-Insurance We are self-insured for medical benefits, and beginning on January 1, 2018 for dental benefits, for all qualifying Zillow Group employees. The medical plan carries a stop-loss policy which will protect when cumulative medical claims exceed 125% of expected claims for the plan year with a limit of $1.0 million and from individual claims during the plan year exceeding $150,000 . We record estimates of the total costs of claims incurred based on an analysis of historical data and independent estimates. Our liability for self-insured claims is included within accrued compensation and benefits in our consolidated balance sheet and was $3.9 million and $2.0 million , respectively, as of December 31, 2018 and 2017

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
Employee Benefit Plan	Employee Benefit Plan We have a defined contribution 401(k) retirement plan covering Zillow Group employees who have met certain eligibility requirements (the “Zillow Group 401(k) Plan”). Eligible employees may contribute pretax compensation up to a maximum amount allowable under the Internal Revenue Service limitations. Employee contributions and earnings thereon vest immediately. We currently match up to 4% of employee contributions under the Zillow Group 401(k) Plan. The total expense related to the Zillow Group 401(k) Plan was $16.0 million , $12.3 million and $10.1 million , respectively, for the years ended December 31, 2018 , 2017 and 2016

Segment Information and Revenue

Segment Information and Revenue	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Segment Information and Revenue	Segment Information and Revenue Beginning in the second quarter of 2018, we have two operating and reportable segments, which have been identified based on the way in which our chief operating decision-maker manages our business, makes operating decisions and evaluates operating performance. Our chief executive officer acts as the chief operating decision-maker and reviews financial and operational information of the IMT and Homes segments. The IMT segment includes the financial results for the Premier Agent, Rentals, Mortgages and new construction marketplaces, dotloop, and display, as well as revenue from the sale of various other marketing and business products and services to real estate professionals. The Homes segment includes the financial results from Zillow Group’s buying and selling of homes directly. Revenue and costs are generally directly attributed to our segments. However, due to the integrated structure of our business, certain costs incurred by one segment may benefit the other segment. These costs are generally headcount-related and are allocated to each segment based on the estimated effort attributable to each segment. Our chief executive officer reviews information about our revenue categories as well as statement of operations data inclusive of loss before income taxes by segment. This information is included in the following table for the period presented (in thousands): Year Ended December 31, 2018 IMT Homes Consolidated Revenue: Premier Agent $ 898,332 $ — $ 898,332 Rentals 134,587 — 134,587 Mortgages 80,046 — 80,046 Other 168,224 — 168,224 Homes — 52,365 52,365 Total revenue 1,281,189 52,365 1,333,554 Costs and expenses: Cost of revenue 104,330 49,260 153,590 Sales and marketing 534,038 18,583 552,621 Technology and development 389,539 21,279 410,818 General and administrative 238,727 23,426 262,153 Impairment costs 79,000 — 79,000 Acquisition-related costs 2,332 — 2,332 Integration costs 2,015 — 2,015 Total costs and expenses 1,349,981 112,548 1,462,529 Income (loss) from operations (68,792 ) (60,183 ) (128,975 ) Other income 19,270 — 19,270 Interest expense (39,078 ) (2,177 ) (41,255 ) Loss before income taxes $ (88,600 ) $ (62,360 ) $ (150,960 ) We have not presented the comparable 2017 or 2016 periods in the table above because we had one

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Entry into Revolving Credit Agreement On January 31, 2019, certain of Zillow Group’s wholly owned subsidiaries entered into a revolving credit agreement with Citibank, N.A., as the directing lender, and certain other parties thereto (the “Credit Agreement”). The Credit Agreement provides for a maximum borrowing capacity of $500.0 million (the “Maximum Amount”) with an initial borrowing capacity of $50.0 million , which amount may be increased up to the Maximum Amount subject to the satisfaction of certain conditions, through a non-recourse credit facility secured by a pledge of the equity of certain subsidiaries that purchase and sell select residential properties through Zillow Offers. The Credit Agreement has an initial term of two years which may be extended for up to one year , subject to the satisfaction of certain conditions. The Credit Agreement includes customary representations and warranties, covenants (including financial covenants applicable to the Company), and provisions regarding events of default. Appointment of CEO; Compensatory Arrangements On February 21, 2019, Zillow Group announced the appointment of Richard N. Barton as Zillow Group’s Chief Executive Officer, effective February 21, 2019. Mr. Barton will succeed Spencer Rascoff, who has served as Zillow Group’s Chief Executive Officer since 2010 and who will remain a member of Zillow Group’s board of directors. Mr. Barton also will remain a member of Zillow Group’s board of directors. In connection with Mr. Rascoff’s resignation as Chief Executive Officer, which occurred on February 21, 2019, Zillow Group entered into an Executive Departure Agreement and Release (the “Agreement”) with Mr. Rascoff. Pursuant to the Agreement, Mr. Rascoff will remain a full-time employee of Zillow Group at his current level of compensation and benefits until March 22, 2019 (the “Departure Date”) in order to provide transition services until such date. Mr. Rascoff will remain a member of Zillow Group’s board of directors.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of PresentationThe accompanying consolidated financial statements include Zillow Group, Inc. and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. These consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles (“GAAP”).
Use of Estimates	Use of EstimatesThe preparation of financial statements in conformity with GAAP requires management to make certain estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and the related disclosures at the date of the financial statements, as well as the reported amounts of revenue and expenses during the periods presented. On an ongoing basis, we evaluate our estimates, including those related to the net realizable value of inventory, amortization period and recoverability of contract cost assets, website and software development costs, recoverability of long-lived assets and intangible assets with definite lives, share-based compensation, income taxes, business combinations, and the recoverability of goodwill and indefinite-lived intangible assets, among others. To the extent there are material differences between these estimates, judgments, or assumptions and actual results, our financial statements will be affected.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments, which potentially subject us to concentrations of credit risk, consist primarily of cash and cash equivalents, investments, accounts receivable and mortgage loans held for sale. We place cash and cash equivalents and investments with major financial institutions, which management assesses to be of high credit quality, in order to limit exposure of our investments. Credit risk with respect to accounts receivable is dispersed due to the large number of customers. There were no customers that comprised 10% or more of our total accounts receivable as of December 31, 2018 and 2017 . Further, our credit risk on accounts receivable is mitigated by the relatively short payment terms that we offer. Collateral is not required for accounts receivable. We maintain an allowance for doubtful accounts such that receivables are stated at net realizable value.
Cash and Cash Equivalents/Restricted Cash	Restricted Cash Restricted cash consists of amounts funded to the reserve and collection accounts related to our Revolving Credit Facility (see Note 14
Short-term Investments	Short-term InvestmentsOur investments consist of fixed income securities, which include U.S. and foreign government agency securities, corporate notes and bonds, commercial paper, municipal securities and certificates of deposit, and are classified as available-for-sale securities. As the investments are available to support current operations, our available-for-sale securities are classified as short-term investments. Available-for-sale securities are carried at fair value with unrealized gains and losses reported as a component of accumulated other comprehensive loss in shareholders’ equity, while realized gains and losses and other-than-temporary impairments are reported as a component of net loss based on specific identification. An impairment charge is recorded in the consolidated statements of operations for declines in fair value below the cost of an individual investment that are deemed to be other than temporary. We assess whether a decline in value is temporary based on the length of time that the fair market value has been below cost, the severity of the decline and the intent and ability to hold or sell the investment.
Accounts Receivable and Allowance for Doubtful Accounts	Accounts Receivable and Allowance for Doubtful Accounts Accounts receivable represent our unconditional right to consideration. Accounts receivable are generally due within 30 days and are recorded net of the allowance for doubtful accounts. We consider accounts outstanding longer than the contractual terms past due. We review accounts receivable on a regular basis and estimate an amount of losses for uncollectible accounts based on our historical collections experience, age of the receivable, knowledge of the customer and the condition of the general economy and industry as a whole. We record changes in our estimate to the allowance for doubtful accounts through bad debt expense and relieve the allowance when accounts are ultimately determined to be uncollectible. Bad debt expense is included in general and administrative expenses.
Mortgage Loans Held for Sale	Mortgage Loans Held for Sale Mortgage loans held for sale includes residential mortgages originated for sale in the secondary market in connection with our October 2018 acquisition of MLOA. We have elected the fair value option for all mortgage loans held for sale as election of this option allows for a better offset of the changes in fair values of the loans and the derivative instruments used to economically hedge them without having to apply complex hedge accounting provisions. Mortgage loans held for sale are initially recorded at fair value based on either sale commitments or current market quotes and are adjusted for subsequent changes in fair value until the loans are sold. Net origination costs and fees associated with mortgage loans are recognized at the time of origination. We sell substantially all of the mortgages we originate and the related servicing rights to third-party purchasers. Interest income is earned from the date a mortgage loan is originated until the loan is sold and is classified within other income in the consolidated statements of operations.
Loan Commitments and Related Derivatives	Loan Commitments and Related Derivatives We are party to interest rate lock commitments (“IRLCs”), which are extended to borrowers who have applied for loan funding and meet defined credit and underwriting criteria in connection with our October 2018 acquisition of MLOA. IRLCs are accounted for as derivative instruments recorded at fair value with gains and losses recognized in revenue in the consolidated statements of operations. We manage our interest rate risk related to IRLCs and mortgage loans held for sale through the use of derivative instruments, generally forward contracts on mortgage-backed securities (“MBS”), which are commitments to either purchase or sell a specified financial instrument at a specified future date for a specified price, and mandatory loan commitments, which are an obligation by an investor to buy loans at a specified price within a specified time period. We do not enter into or hold derivatives for trading or speculative purposes and our derivatives are not designated as hedging instruments. Changes in the fair value of our derivative financial instruments are recognized in revenues in our consolidated statements of operations, and the fair values are reflected in other assets or other liabilities, as applicable. The net change in fair value was not significant for the year ended December 31, 2018.
Inventory	Inventory Inventory is comprised of homes acquired through our Zillow Offers program and is stated at the lower of cost or net realizable value. Homes are removed from inventory on a specific identification basis when they are resold. Stated cost includes consideration paid to acquire and update each home including associated allocated overhead costs. Work-in-progress inventory includes homes undergoing updates and finished goods inventory includes homes ready for resale. Unallocated overhead costs are expensed as incurred and included in cost of revenue. Selling costs, including commissions, escrow and title fees, staging, and holding costs, including utilities, taxes and maintenance, are expensed as incurred and included in sales and marketing expenses.
Property and Equipment	Property and Equipment Property and equipment is recorded at cost and depreciated using the straight-line method over the estimated useful lives of the related assets. The useful lives are as follows: Computer equipment 2 to 3 years Office equipment, furniture and fixtures 5 to 7 years Leasehold improvements Shorter of expected useful life or lease term
Website and Software Development Costs	Website and Software Development Costs The costs incurred in the preliminary stages of development are expensed as incurred. Once an application has reached the development stage, internal and external costs, if direct and incremental and deemed by management to be significant, are capitalized in property and equipment and amortized on a straight-line basis over their estimated useful lives. Maintenance and enhancement costs, including those costs in the post-implementation stages, are typically expensed as incurred, unless such costs relate to substantial upgrades and enhancements to the website or software that result in added functionality, in which case the costs are capitalized and amortized on a straight-line basis over the estimated useful lives. Amortization expense related to capitalized website and software development costs is included in technology and development expense. Capitalized development activities placed in service are amortized over the expected useful lives of those releases, currently estimated at one to three years
Recoverability of Goodwill and Indefinite-Lived Intangible Assets	Recoverability of Goodwill and Indefinite-Lived Intangible Assets Goodwill represents the excess of the cost of an acquired business over the fair value of the assets acquired at the date of acquisition, and is not amortized. We assess the impairment of goodwill on an annual basis, in our fourth quarter, or whenever events or changes in circumstances indicate that goodwill may be impaired. Typically, we choose to forgo the initial qualitative assessment and perform a quantitative analysis to assist in our annual evaluation. If impairment exists, the carrying value of the goodwill is reduced to fair value through an impairment charge recorded in our statements of operations.
Intangible Assets/Recoverability of Intangible Assets with Definite Lives and Other Long-Lived Assets	Intangible Assets We purchase and license data content from multiple data providers. This data content consists of U.S. county data about home details (e.g., the number of bedrooms, bathrooms, square footage) and other information relating to the purchase price of homes, both current and historical, as well as imagery, mapping and parcel data that is displayed on our mobile applications and websites. Our home details data not only provides information about a home and its related transactions which is displayed on our mobile applications and websites, but is also used in our proprietary valuation algorithms to produce Zestimates, Rent Zestimates and Zillow Home Value Indexes. License agreement terms vary by vendor. In some instances, we retain perpetual rights to this information after the contract ends; in other instances, the information and data are licensed only during the fixed term of the agreement. Additionally, certain data license agreements provide for uneven payment amounts throughout the contract term. We capitalize payments made to third parties for data licenses that we expect to provide future economic benefit through the recovery of the costs of these arrangements via the generation of our revenue and margins. For data license contracts that include uneven payment amounts, we capitalize the payments as they are made as an intangible asset and the total contract value is typically amortized on a straight-line basis over the term of the contract, which is equivalent to the estimated useful life of the asset. We evaluate data content contracts for potential capitalization at the inception of the arrangement as well as each time periodic payments to third parties are made. The amortization period for the capitalized purchased content is based on our best estimate of the useful life of the asset, which is approximately five years . The determination of the useful life includes consideration of a variety of factors including, but not limited to, our assessment of the expected use of the asset and contractual provisions that may limit the useful life, as well as an assessment of when the data is expected to become obsolete based on our estimates of the diminishing value of the data over time. We evaluate the useful life of the capitalized purchased data content each reporting period to determine whether events and circumstances warrant a revision to the remaining useful life. If we determine the estimate of the asset’s useful life requires modification, the carrying amount of the asset is amortized prospectively over the revised useful life. The capitalized purchased data content is amortized on a straight-line basis as the pattern of delivery of the economic benefits of the data cannot reliably be determined because we do not have the ability to reliably predict future traffic to our mobile applications and websites. Under certain other data agreements, the underlying data is obtained on a subscription basis with consistent monthly or quarterly recurring payment terms over the contractual period. Upon the expiration of such arrangements, we no longer have the right to access the related data, and therefore, the costs incurred under such contracts are not capitalized and are expensed as payments are made. We would immediately lose rights to data under these arrangements if we were to cancel the subscription and/or cease making payments under the subscription arrangements. We also capitalize costs related to the license of certain internal-use software from third parties, including certain licenses of software in cloud computing arrangements. Additionally, we capitalize costs incurred during the application development stage related to the development of internal-use software and enterprise cloud computing services. We expense costs as incurred related to the planning and post-implementation phases of development. Capitalized internal-use software costs are amortized over the estimated useful life of the asset, which is currently one to 3 years , on a straight-line basis. Intangibles-in-progress consist of purchased content and software that are capitalizable but have not been placed in service. We also have intangible assets for developed technology, customer relationships, trade names and trademarks and advertising relationships which we recorded in connection with acquisitions. Purchased intangible assets with a determinable economic life are carried at cost, less accumulated amortization. These intangible assets are amortized over the estimated useful life of the asset on a straight-line basis. Recoverability of Intangible Assets with Definite Lives and Other Long-Lived Assets
Contract Cost Assets/Revenue Recognition	Contract Cost AssetsWe capitalize certain incremental costs of obtaining contracts with customers which we expect to recover. These costs relate to commissions paid to sales personnel, primarily for our Premier Agent and Premier Broker programs. As a practical expedient, we recognize the incremental costs of obtaining a contract as an expense when incurred if the amortization period of the asset that we otherwise would have recognized is one year or less. Capitalized commission costs are recorded as contract cost assets in our consolidated balance sheets. Contract cost assets are amortized to expense on a straight-line basis over a period that is consistent with the transfer to the customer of the products or services to which the asset relates, generally the estimated life of the customer relationship. Amortization expense related to contract cost assets is included in sales and marketing expenses in our consolidated statements of operations. In determining the estimated life of our customer relationships, we consider quantitative and qualitative data, including, but not limited to, historical customer data, recent changes or expected changes in product or service offerings, and changes in how we monetize our products and services. The amortization period for capitalized contract costs related to our Premier Agent and Premier Broker programs ranges from two to three years.Revenue Recognition We recognize revenue when (or as) we satisfy our performance obligations by transferring control of the promised products or services to our customers in an amount that reflects the consideration to which we expect to be entitled in exchange for those products or services. As a practical expedient, we do not adjust the promised amount of consideration for the effects of a significant financing component as the period between our transfer of a promised product or service to a customer and when the customer pays for that product or service is one year or less. We do not disclose the transaction price related to remaining performance obligations for (i) contracts with an original expected duration of one year or less and (ii) contracts for which we recognize revenue at the amount to which we have the right to invoice for performance completed to date. The remaining duration of our performance obligations is generally less than one year. In our Internet, Media & Technology (“IMT”) segment, we generate revenue from the sale of advertising services and our suite of marketing software and technology solutions to businesses and professionals primarily associated with the residential real estate, rental and mortgage industries. These professionals include real estate, rental and mortgage professionals and brand advertisers. Our four primary revenue categories within our IMT segment are Premier Agent, Rentals, Mortgages and Other. In our Homes segment, we generate revenue from the resale of homes on the open market through our Zillow Offers program. Premier Agent Revenue. Premier Agent revenue is derived from our Premier Agent and Premier Broker programs. Our Premier Agent and Premier Broker programs offer a suite of marketing and business technology products and services to help real estate agents and brokers achieve their advertising goals, while growing and managing their businesses and brands. All Premier Agents and Premier Brokers receive access to a dashboard portal on our mobile application or website that provides individualized program performance analytics, our customer relationship management, or CRM, tool that captures detailed information about each contact made with a Premier Agent or Premier Broker through our mobile and web platforms and our account management tools. We have concluded that the marketing and business technology products and services promised to Premier Agents and Premier Brokers represent distinct performance obligations. We primarily offer our Premier Agent and Premier Broker advertising products on a cost per impression basis. Payment is received prior to the delivery of impressions. Impressions are delivered when a sold advertisement appears on pages viewed by users of our mobile applications and websites. We determine the cost per impression delivered in each zip code using an auction-based pricing method in consideration of the total amount spent by Premier Agents and Premier Brokers to purchase impressions in the zip code during the month. A Premier Agent’s or Premier Broker’s share of voice in a zip code is determined by their proportional monthly budgeted spend in that zip code as a percentage of the total monthly budgeted spend of all Premier Agents and Premier Brokers in that zip code. The cost per impression that we charge is dynamic - as demand for impressions in a zip code increases or decreases, the cost per impression in that zip code may be increased or decreased accordingly. The price paid for each impression is representative of the price at which we would sell an impression separately to a customer, or the stand-alone selling price. We have not allocated the transaction price to each performance obligation as the amounts recognized would be the same irrespective of any allocation. As such, we recognize revenue related to the Premier Agent and Premier Broker products and services based on the contractual spend recognized on a straight-line basis during the contractual period over which the products and services are provided. This methodology best depicts how we satisfy our performance obligations to customers, as we continuously transfer control of the performance obligations to the customer throughout the contractual period. In October 2018, we began testing a new Flex Pricing model for Premier Broker and Premier Agent advertising services in limited markets. With the Flex Pricing model, Premier Brokers and Premier Agents are provided with validated leads at no upfront cost, and they pay a performance advertising fee only when a real estate transaction is closed with one of their leads. With this pricing model, the transaction price represents variable consideration as the amount to which we expect to be entitled varies based on the number of validated leads that convert into real estate transactions. Rentals Revenue. Rentals revenue includes our rentals marketplace and suite of tools for rental professionals. Rentals revenue primarily includes revenue generated by advertising sold to property managers and other rental professionals on a cost per lead, cost per click or cost per lease generated basis. We recognize revenue as leads or clicks are provided to rental professionals, which is the amount for which we have the right to invoice. The number of leases generated through our rentals marketplace during the period is accounted for as variable consideration, and we estimate these amounts based on the expected number of qualified leases secured during the period. We do not believe that a significant reversal in the amount of cumulative revenue recognized will occur once the uncertainty related to the number of leases secured is subsequently resolved. Beginning in 2018, rentals revenue also includes revenue generated from Zillow’s rental applications product through which potential renters can submit applications to multiple rental properties over a 30-day period for a flat service fee. We recognize revenue for the rental applications product on a straight-line basis during the contractual period over which the customer has the right to access and submit the rental application. Mortgages Revenue. Mortgages revenue primarily includes marketing products sold to mortgage professionals on a cost per lead basis, including our Custom Quote and a portion of our Connect (formerly known as Long Form) services, and on a subscription basis, including a portion of our Connect service. For our Connect and Custom Quote cost per lead mortgage marketing products, participating qualified mortgage professionals typically make a prepayment to gain access to consumers interested in connecting with mortgage professionals. Mortgage professionals who exhaust their initial prepayment prepay additional funds to continue to participate in the marketplace. For our Connect subscription mortgage marketing product, participating qualified mortgage professionals generally prepay a monthly subscription fee, which they then allocate to desired geographic counties. In Zillow Group’s Connect platform, consumers answer a series of questions to find a local lender, and mortgage professionals receive consumer contact information, or leads, when the consumer chooses to share their information with a lender. Consumers who request rates for mortgage loans in Custom Quotes are presented with customized quotes from participating mortgage professionals. For our cost per lead mortgages products, we recognize revenue when a user contacts a mortgage professional through Zillow Group’s mortgages platform, which is the amount for which we have the right to invoice. For our Connect subscription product, the opportunity to receive a consumer contact is based on the mortgage professional’s relative share of voice in a geographic county. When a consumer submits a contact, Zillow Group contacts a group of subscription mortgage professionals via text message, and the first mortgage professional to respond receives the consumer contact information. We recognize revenue based on the contractual spend recognized on a straight-line basis during the contractual period over which the service is provided. This methodology best depicts how we satisfy our performance obligation to subscription customers, as we continuously transfer control of the performance obligation to the customer throughout the contractual period. Beginning in October 2018, mortgages revenue also includes revenue generated from our mortgage originations business. We elect the fair value option for our mortgage loans held for sale, which are initially recorded at fair value based on either sale commitments or current market quotes and are adjusted for subsequent changes in fair value until the loans are closed. Mortgages revenue also includes revenue generated by Mortech, which provides subscription-based mortgage software solutions, including a product and pricing engine and lead management platform, for which we recognize revenue on a straight-line basis during the contractual period over which the services are provided. Other Revenue. Other revenue primarily includes revenue generated by new construction and display, as well as revenue from the sale of various other marketing and business products and services to real estate professionals. Our new construction marketing solutions allow home builders to showcase their available inventory to home shoppers. New construction revenue primarily includes revenue generated by advertising sold to builders on a cost per residential community basis, and revenue is recognized on a straight-line basis during the contractual period over which the communities are advertised on our mobile applications and websites. Consideration is billed in arrears. Display revenue primarily consists of graphical mobile and web advertising sold on a cost per thousand impressions or cost per click basis to advertisers promoting their brands on our mobile applications and websites. We recognize display revenue as clicks occur or as impressions are delivered to users interacting with our mobile applications or websites, which is the amount for which we have the right to invoice. Homes Revenue. Homes revenue is derived from the resale of homes on the open market through our Zillow Offers program. Homes revenue is recognized at the time of the closing of the home sale when title to and possession of the property are transferred to the buyer. There were no customers that generated 10% or more of our total revenue in the years ended December 31, 2018 , 2017 or 2016 . Cost of Revenue
Deferred Rent	Deferred RentFor our operating leases, we recognize rent expense on a straight-line basis over the terms of the leases and, accordingly, we record the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. For office space under an operating lease that is subleased to a third party for which we intend to reoccupy the space at a future date, rent expense is recognized net of sublease income. Landlord-funded leasehold improvements are also recorded as deferred rent liabilities and are amortized as a reduction of rent expense over the non-cancelable term of the related operating lease.
Business Combinations	Business CombinationsWe recognize identifiable assets acquired and liabilities assumed at their acquisition date fair values. Goodwill as of the acquisition date is measured as the excess of consideration transferred over the net of the acquisition date fair values of the assets acquired and the liabilities assumed. While we use our best estimates and assumptions for the purchase price allocation process to value assets acquired and liabilities assumed at the acquisition date, our estimates are inherently uncertain and subject to refinement. As a result, during the measurement period, which may be up to one year from the acquisition date, we record adjustments to the assets acquired and liabilities assumed, with the corresponding offset to goodwill to the extent that we identify adjustments to the preliminary purchase price allocation. Upon the conclusion of the measurement period or final determination of the values of assets acquired or liabilities assumed, whichever comes first, any subsequent adjustments are recorded to our consolidated statements of operations. We recognize adjustments to provisional amounts that are identified during the measurement period in the reporting period in which the adjustment amounts are determined.
Technology and Development	Technology and Development Technology and development expenses consist of headcount expenses, including salaries, benefits, share-based compensation expense and bonuses for salaried employees and contractors engaged in the design, development and testing of our mobile applications and websites and the tools and applications that support our products, and equipment and maintenance costs. Technology and development expenses also include amortization costs related to capitalized website and development activities, amortization of software, amortization of certain intangibles and other data agreement costs related to the purchase of data used to populate our mobile applications and websites, amortization of intangible assets recorded in connection with acquisitions, including developed technology and customer relationships, amongst others, and depreciation expense.
Share-Based Compensation	Share-Based Compensation We measure compensation expense for all share-based awards at fair value on the date of grant and recognize compensation expense over the service period on a straight-line basis for awards expected to vest. We use the Black-Scholes-Merton option-pricing model to determine the fair value for option awards. In valuing our option awards, we make assumptions about risk-free interest rates, dividend yields, volatility, and weighted-average expected lives. In addition, through December 31, 2016, we made assumptions about estimated forfeiture rates. Beginning on January 1, 2017, we elected to account for forfeitures as they occur. Risk-free interest rates are derived from U.S. Treasury securities as of the option award grant date. Expected dividend yield is based on our historical cash dividend payments, which have been zero to date. The expected volatility for our Class A common stock and Class C capital stock is estimated using our historical volatility. The weighted-average expected life of the option awards is estimated based on our historical exercise data. Prior to January 1, 2017, forfeiture rates were estimated using historical actual forfeiture trends as well as our judgment of future forfeitures. These rates were evaluated at least quarterly and any change in share-based compensation expense was recognized in the period of the change. We considered many factors when estimating expected forfeitures, including employee class and historical experience.
Advertising Costs	Advertising costs are recorded in sales and marketing expenses.Advertising CostsAdvertising costs are expensed as incurred.
Income Taxes	Income Taxes We use the asset and liability approach for accounting and reporting income taxes, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the financial statement and tax bases of assets and liabilities at the applicable enacted tax rates. A valuation allowance against deferred tax assets would be established if, based on the weight of available evidence, it is more likely than not (a likelihood of more than 50%) that some or all of the deferred tax assets are not expected to be realized. We establish reserves for tax-related uncertainties based on estimates of whether, and the extent to which, additional taxes will be due. We adjust these reserves in light of changing facts and circumstances, such as the closing of a tax audit, new tax legislation or the change of an estimate. To the extent that the final tax outcome of these matters is different than the amounts recorded, such differences will affect the provision for income taxes in the period in which such determination is made. Interest and penalties related to unrecognized tax benefits are recorded as income tax expense. On December 22, 2017, the U.S. government enacted comprehensive tax legislation under the Tax Cuts and Jobs Act (the “Tax Act”). The Tax Act makes broad and complex changes to the U.S. tax code, including but not limited to: (1) reducing the U.S. federal corporate tax rate from 35 percent to 21 percent ; (2) requiring companies to pay a one-time transition tax on certain unrepatriated earnings of foreign subsidiaries; (3) generally eliminating U.S. federal income taxes on dividends from foreign subsidiaries; (4) eliminating the corporate alternative minimum tax (“AMT”) and how AMT credits are utilized; (5) the additional limitations on deducting executive compensation under IRC Section 162(m); and (6) changing rules related to uses and limitations of net operating loss carryforwards created in tax years beginning after December 31, 2017
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards In December 2016, the Financial Accounting Standards Board (“FASB”) issued guidance to narrow the definition of a business. This guidance assists entities with evaluating when a set of transferred assets and activities is a business. This guidance is effective for interim and annual reporting periods beginning after December 15, 2017, and early adoption is permitted. This guidance must be applied prospectively to transactions occurring within the period of adoption. We adopted this guidance on January 1, 2018. The adoption of this guidance did not have an impact on our financial position, results of operations or cash flows. In January 2016, the FASB issued guidance on the recognition and measurement of financial instruments. This guidance generally requires equity investments, except those accounted for under the equity method of accounting or those that result in consolidation of the investee, to be measured at fair value with changes in fair value recognized in net income (loss). An entity may elect to measure equity securities that do not have readily determinable fair values and do not qualify for the net asset value per share practical expedient at cost minus impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer. The guidance also requires the separate presentation of financial assets and financial liabilities by measurement category and form of financial asset on the balance sheet or the accompanying notes to the financial statements. This guidance is effective for interim and annual reporting periods beginning after December 15, 2017, early adoption is permitted, and the guidance must be applied prospectively to equity investments that exist as of the adoption date. We adopted this guidance, and the February 2018 amendment to this guidance, effective January 1, 2018. The adoption of this guidance did not have any impact on our financial position, results of operations or cash flows. In May 2014, the FASB issued guidance on revenue from contracts with customers. The guidance states that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those products or services. It also states that an entity should recognize as an asset the incremental costs of obtaining a contract that the entity expects to recover and amortize the costs consistent with the transfer to the customer of the products or services to which the asset relates. The guidance requires more detailed disclosures to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. We adopted this guidance effective January 1, 2018 using the modified retrospective transition approach applied to all contracts at the date of initial application. We recorded an adjustment of $40.3 million to decrease accumulated deficit as of January 1, 2018 related to the accounting for the cost of sales commissions, primarily related to sales commissions for our Premier Agent and Premier Broker advertising products. Historically, we expensed these sales commission costs as incurred, but under the new guidance, the cost of certain sales commissions is recorded as a contract cost asset and recognized as an operating expense over the period that we expect to recover the costs. The amount by which each financial statement line item is affected by the application of this guidance as of and for the year ended December 31, 2018 is as follows (in thousands, except per share data): New Guidance Prior Guidance Change Consolidated Statement of Operations: Sales and marketing $ 552,621 $ 558,118 $ (5,497 ) Total costs and expenses 1,462,529 1,468,026 (5,497 ) Loss from operations (128,975 ) (134,472 ) 5,497 Loss before income taxes (150,960 ) (156,457 ) 5,497 Income tax benefit 31,102 32,024 (922 ) Net loss (119,858 ) (124,433 ) 4,575 Net loss per share — basic and diluted (0.61 ) (0.63 ) 0.02 Consolidated Balance Sheet: Contract cost assets 45,819 — 45,819 Total assets 4,291,116 4,245,297 45,819 Deferred tax liabilities and other long-term liabilities 17,474 16,552 922 Total liabilities 1,023,937 1,023,015 922 Accumulated deficit (671,779 ) (716,676 ) 44,897 Total shareholders’ equity 3,267,179 3,222,282 44,897 Total liabilities and shareholders’ equity $ 4,291,116 $ 4,245,297 $ 45,819 Recently Issued Accounting Standards Not Yet Adopted In August 2018, the FASB issued guidance related to a customer’s accounting for implementation costs incurred in hosting arrangements. The guidance aligns the requirements for capitalizing implementation costs incurred in cloud computing arrangements with the requirements for capitalizing costs to develop or obtain internal-use software. This guidance is effective for interim and annual reporting periods beginning after December 15, 2019, and early adoption is permitted. This guidance may be applied either retrospectively or prospectively. We expect to adopt this guidance on January 1, 2020. We have not yet determined the impact the adoption of this guidance will have on our financial position, results of operations or cash flows. In August 2018, the FASB issued guidance related to disclosure requirements for fair value measurements. This guidance removes, modifies and adds disclosures related to fair value measurements. This guidance is effective for interim and annual periods beginning after December 15, 2019, and early adoption is permitted. The amendments on changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements and the narrative description of measurement uncertainty should be applied prospectively for only the most recent interim and annual period presented in the initial fiscal year of adoption. All other amendments should be applied retrospectively to all periods presented upon their effective date. We expect to adopt this guidance on January 1, 2020. We have not yet determined the impact the adoption of this guidance will have on our financial statement disclosures. In June 2018, the FASB issued guidance related to contributions received and made. This guidance assists entities with evaluating whether a transfer of assets is considered a contribution or an exchange transaction. This guidance is effective for interim and annual reporting periods beginning after June 15, 2018 for contributions received and after December 15, 2018 for contributions made, and early adoption is permitted. The guidance should be applied on a modified prospective basis, though retrospective application is permitted. We adopted this guidance on January 1, 2019. The adoption of this guidance is not expected to have a material impact on our financial position, results of operations or cash flows. In February 2018, the FASB issued guidance on income tax accounting related to the Tax Act. This guidance permits a reclassification from accumulated other comprehensive income (loss) to accumulated deficit for the adjustment of deferred taxes due to the reduction of the historical corporate income tax rate to the newly enacted corporate income tax rate under the Tax Act. It also requires certain disclosures regarding these reclassifications. The guidance is effective for interim and annual reporting periods beginning after December 15, 2018, and early adoption is permitted. This guidance must be applied either on a prospective basis in the period of adoption or retrospectively to each period in which the effect of the change in the corporate income tax rate is recognized. We adopted this guidance on January 1, 2019. The adoption of this guidance is not expected to have a material impact on our financial position, results of operations or cash flows. In March 2017, the FASB issued guidance related to the premium amortization on purchased callable debt securities. This guidance shortens the amortization period for certain callable debt securities purchased at a premium by requiring that the premium be amortized to the earliest call date. This guidance is effective for interim and annual reporting periods beginning after December 15, 2018, and early adoption is permitted. This guidance must be applied on a modified retrospective basis through a cumulative-effect adjustment directly to retained earnings as of the beginning of the period of adoption. We adopted this guidance on January 1, 2019. The adoption of this guidance is not expected to have a material impact on our financial position, results of operations or cash flows. In June 2016, the FASB issued guidance on the measurement of credit losses on financial instruments. This guidance requires the use of an expected loss impairment model for instruments measured at amortized cost. For available-for-sale debt securities, an entity is required to recognize credit losses through an allowance for credit losses rather than as a write-down. This guidance is effective for interim and annual reporting periods beginning after December 15, 2019, and early adoption is permitted for interim and annual reporting periods beginning after December 15, 2018. The adoption of this guidance requires a cumulative-effect adjustment to retained earnings as of the beginning of the first reporting period in which the guidance is effective. We expect to adopt this guidance on January 1, 2020. We have not yet determined the impact the adoption of this guidance will have on our financial position, results of operations or cash flows. In February 2016, the FASB issued guidance on leases. This guidance requires the recognition of a right-of-use asset and lease liability on the balance sheet for all leases. This guidance also requires more detailed disclosures to enable users of financial statements to understand the amount, timing, and uncertainty of cash flows arising from leases. This guidance is effective for interim and annual reporting periods beginning after December 15, 2018. In July 2018, the FASB issued certain targeted improvements to the accounting and disclosure requirements for leases, including an additional optional transition method that allows entities to initially apply the new standard at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption without restating prior periods. When adopting the lease guidance, an entity may elect a practical expedient package, under which it need not reassess (a) whether any expired or existing contracts are or contain leases; (b) the lease classification for any expired or existing leases; and (c) initial direct costs for any existing leases. These three practical expedients must be elected as a package and must be consistently applied to all existing leases at the date of adoption. We adopted the new guidance on leases on January 1, 2019 using the optional transition method and electing to adopt the practical expedient package. Under this approach, we will not restate the prior financial statements presented. Based on our lease portfolio as of December 31, 2018, we anticipate recording on our consolidated balance sheet right-of-use assets of approximately $90 million as well as operating lease liabilities of approximately $115 million
Fair Value	Accounting standards define fair value as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market in an orderly transaction between market participants on the measurement date. The standards also establish a fair value hierarchy, which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. There are three levels of inputs that may be used to measure fair value: • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Assets and liabilities valued based on observable market data for similar instruments, such as quoted prices for similar assets or liabilities. • Level 3—Unobservable inputs that are supported by little or no market activity; instruments valued based on the best available data, some of which is internally developed, and considers risk premiums that a market participant would require. We applied the following methods and assumptions in estimating our fair value measurements: Cash equivalents —The fair value measurement of money market funds is based on quoted market prices in active markets. The fair value measurement of corporate notes and bonds, commercial paper, U.S. government agency securities and certificates of deposit 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. Short-term investments —The fair value measurement of our short-term investments 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. Restricted cash —The carrying value of restricted cash approximates fair value due to the short period of time amounts borrowed on the Revolving Credit Facility (see Note 14 ) are outstanding. Further, the carrying value of restricted cash related to escrow amounts held as part of the mortgage originations business also approximates fair value due to the short period of time amounts are held in escrow before they are transferred to the appropriate party, typically a home seller or bank. Mortgage loans held for sale —The fair value of mortgage loans held for sale is generally calculated by reference to quoted prices in secondary markets for commitments to sell mortgage loans with similar characteristics. Interest rate lock commitments —The fair value of interest rate lock commitments is calculated by reference to quoted prices in secondary markets for commitments to sell mortgage loans with similar characteristics. Any expired commitments are excluded from the fair value measurement. We generally only issue IRLCs for products that meet specific purchaser guidelines. Since not all IRLCs will become closed loans, we adjust our fair value measurements for the estimated amount of IRLCs that will not close. Forward contracts
Net Loss Per Share	Basic net loss per share is computed by dividing net loss by the weighted-average number of shares (including Class A common stock, Class B common stock and Class C capital stock) outstanding during the period. In the calculation of basic net loss per share, undistributed earnings are allocated assuming all earnings during the period were distributed.Diluted net loss per share is computed by dividing net loss by the weighted-average number of shares (including Class A common stock, Class B common stock and Class C capital stock) outstanding during the period and potentially dilutive Class A common stock and Class C capital stock equivalents, except in cases where the effect of the Class A common stock or Class C capital stock equivalent would be antidilutive. Potential Class A common stock and Class C capital stock equivalents consist of Class A common stock and Class C capital stock issuable upon exercise of stock options and Class A common stock and Class C capital stock underlying unvested restricted stock awards and unvested restricted stock units using the treasury stock method. Potential Class A common stock equivalents also include Class A common stock issuable upon conversion of the 2020 Notes using the if-converted method.
Segment Information and Revenue	Beginning in the second quarter of 2018, we have two operating and reportable segments, which have been identified based on the way in which our chief operating decision-maker manages our business, makes operating decisions and evaluates operating performance. Our chief executive officer acts as the chief operating decision-maker and reviews financial and operational information of the IMT and Homes segments. The IMT segment includes the financial results for the Premier Agent, Rentals, Mortgages and new construction marketplaces, dotloop, and display, as well as revenue from the sale of various other marketing and business products and services to real estate professionals. The Homes segment includes the financial results from Zillow Group’s buying and selling of homes directly.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Useful Lives	Property and equipment is recorded at cost and depreciated using the straight-line method over the estimated useful lives of the related assets. The useful lives are as follows: Computer equipment 2 to 3 years Office equipment, furniture and fixtures 5 to 7 years Leasehold improvements Shorter of expected useful life or lease term
Schedule of Effect of Application of New Guidance	The amount by which each financial statement line item is affected by the application of this guidance as of and for the year ended December 31, 2018 is as follows (in thousands, except per share data): New Guidance Prior Guidance Change Consolidated Statement of Operations: Sales and marketing $ 552,621 $ 558,118 $ (5,497 ) Total costs and expenses 1,462,529 1,468,026 (5,497 ) Loss from operations (128,975 ) (134,472 ) 5,497 Loss before income taxes (150,960 ) (156,457 ) 5,497 Income tax benefit 31,102 32,024 (922 ) Net loss (119,858 ) (124,433 ) 4,575 Net loss per share — basic and diluted (0.61 ) (0.63 ) 0.02 Consolidated Balance Sheet: Contract cost assets 45,819 — 45,819 Total assets 4,291,116 4,245,297 45,819 Deferred tax liabilities and other long-term liabilities 17,474 16,552 922 Total liabilities 1,023,937 1,023,015 922 Accumulated deficit (671,779 ) (716,676 ) 44,897 Total shareholders’ equity 3,267,179 3,222,282 44,897 Total liabilities and shareholders’ equity $ 4,291,116 $ 4,245,297 $ 45,819

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Summary of Balances of Cash Equivalents and Investments	The following tables present the balances of assets measured at fair value on a recurring basis, by level within the fair value hierarchy, as of the dates presented (in thousands): December 31, 2018 Total Level 1 Level 2 Cash equivalents: Money market funds $ 541,575 $ 541,575 $ — Commercial paper 3,999 — 3,999 Short-term investments: U.S. government agency securities 646,496 — 646,496 Corporate notes and bonds 112,933 — 112,933 Commercial paper 85,506 — 85,506 Municipal securities 39,306 — 39,306 Foreign government securities 14,915 — 14,915 Certificates of deposit 4,711 — 4,711 Mortgage origination-related: Mortgage loans held for sale 35,409 — 35,409 Interest rate lock commitments 847 — 847 Forward contracts (125 ) — (125 ) Total $ 1,485,572 $ 541,575 $ 943,997 December 31, 2017 Total Level 1 Level 2 Cash equivalents: Money market funds $ 233,508 $ 233,508 $ — Corporate notes and bonds 6,199 — 6,199 Commercial paper 3,987 — 3,987 U.S. government agency securities 1,748 — 1,748 Certificates of deposit 249 — 249 Short-term investments: U.S. government agency securities 298,758 — 298,758 Corporate notes and bonds 44,607 — 44,607 Commercial paper 39,325 — 39,325 Municipal securities 11,459 — 11,459 Certificates of deposit 10,297 — 10,297 Foreign government securities 5,998 — 5,998 Total $ 656,135 $ 233,508 $ 422,627

Cash and Cash Equivalents, Sh_2

Cash and Cash Equivalents, Short-term Investments and Restricted Cash (Tables)	12 Months Ended
	Dec. 31, 2018
Cash and Cash Equivalents [Abstract]
Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Market Value of Cash and Cash Equivalents and Short-term Investments	The following tables present the amortized cost, gross unrealized gains and losses and estimated fair market value of our cash and cash equivalents, available-for-sale investments and restricted cash as of the dates presented (in thousands): December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Market Value Cash $ 105,484 $ — $ — $ 105,484 Cash equivalents: Money market funds 541,575 — — 541,575 Commercial paper 3,999 — — 3,999 Short-term investments: U.S. government agency securities 647,266 51 (821 ) 646,496 Corporate notes and bonds 113,109 1 (177 ) 112,933 Commercial paper 85,506 — — 85,506 Municipal securities 39,316 23 (33 ) 39,306 Foreign government securities 14,929 — (14 ) 14,915 Certificates of deposit 4,711 1 (1 ) 4,711 Restricted cash 12,385 — — 12,385 Total $ 1,568,280 $ 76 $ (1,046 ) $ 1,567,310 December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Market Value Cash $ 106,404 $ — $ — $ 106,404 Cash equivalents: Money market funds 233,508 — — 233,508 Corporate notes and bonds 6,200 — (1 ) 6,199 Commercial paper 3,987 — — 3,987 U.S. government agency securities 1,748 — — 1,748 Certificates of deposit 249 — — 249 Short-term investments: U.S. government agency securities 299,814 — (1,056 ) 298,758 Corporate notes and bonds 44,661 1 (55 ) 44,607 Commercial paper 39,325 — — 39,325 Municipal securities 11,494 — (35 ) 11,459 Certificates of deposit 10,296 2 (1 ) 10,297 Foreign government securities 6,000 — (2 ) 5,998 Total $ 763,686 $ 3 $ (1,150 ) $ 762,539
Available-for-Sale Investments by Contractual Maturity	The following table presents available-for-sale investments by contractual maturity date as of December 31, 2018 (in thousands): Amortized Cost Estimated Fair Market Value Due in one year or less $ 801,828 $ 800,827 Due after one year through two years 103,009 103,040 Total $ 904,837 $ 903,867

Accounts Receivable, Net (Table

Accounts Receivable, Net (Tables)	12 Months Ended
	Dec. 31, 2018
Receivables [Abstract]
Accounts Receivable	The following table presents the detail of accounts receivable as of the dates presented (in thousands): December 31, 2018 2017 Accounts receivable $ 61,134 $ 51,334 Unbilled accounts receivable 9,787 8,403 Less: allowance for doubtful accounts (4,838 ) (5,341 ) Accounts receivable, net $ 66,083 $ 54,396
Allowance for Doubtful Accounts	The following table presents the changes in the allowance for doubtful accounts for the periods presented (in thousands): Year Ended December 31, 2018 2017 2016 Allowance for doubtful accounts: Balance, beginning of period $ 5,341 $ 1,337 $ 3,378 Additions charged to expense 869 7,349 2,681 Less: write-offs, net of recoveries and other adjustments (1,372 ) (3,345 ) (4,722 ) Balance, end of period $ 4,838 $ 5,341 $ 1,337

Inventory (Tables)

Inventory (Tables)	12 Months Ended
	Dec. 31, 2018
Inventory Disclosure [Abstract]
Components of Net Inventory	The components of inventory, net of applicable lower of cost or net realizable value write-downs, were as follows for the periods presented (in thousands): December 31, 2018 2017 Work-in-progress $ 45,943 $ — Finished goods 116,886 — Inventory $ 162,829 $ —

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Detail of Property and Equipment	The following table presents the detail of property and equipment as of the dates presented (in thousands): December 31, 2018 2017 Website development costs $ 149,891 $ 130,072 Computer equipment 22,477 30,071 Leasehold improvements 65,012 47,321 Construction-in-progress 29,037 28,150 Office equipment, furniture and fixtures 39,510 22,887 Property and equipment 305,927 258,501 Less: accumulated amortization and depreciation (170,755 ) (146,230 ) Property and equipment, net $ 135,172 $ 112,271

Acquisitions and Equity Inves_2

Acquisitions and Equity Investments (Tables)	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Purchase Price Allocation	Based upon the fair values determined by us, in which we considered or relied in part upon a valuation report of a third-party expert, the total purchase price was allocated as follows (in thousands): Cash and cash equivalents $ 10,796 Restricted cash 753 Mortgage loans available for sale 34,248 Property, plant and equipment 1,315 Intangible assets 2,600 Goodwill 53,831 Other acquired assets 3,079 Accounts payable (1,953 ) Accrued expenses (2,591 ) Warehouse lines of credit (32,536 ) Other assumed liabilities (2,855 ) Total purchase price $ 66,687 Current assets $ 371 Identifiable intangible assets 3,700 Goodwill 10,610 Current liabilities (101 ) Deferred tax liabilities (1,416 ) Total purchase price $ 13,164

Goodwill (Tables)

Goodwill (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Change in Goodwill	The following table presents the change in goodwill from December 31, 2017 through December 31, 2018 (in thousands): Balance as of December 31, 2017 $ 1,931,076 Goodwill recorded in connection with acquisition of MLOA 53,831 Balance as of December 31, 2018 $ 1,984,907

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	The following tables present the detail of intangible assets subject to amortization as of the dates presented (in thousands): December 31, 2018 Cost Accumulated Amortization Net Purchased content $ 42,110 $ (30,477 ) $ 11,633 Software 24,296 (13,925 ) 10,371 Customer relationships 103,900 (60,733 ) 43,167 Developed technology 111,980 (72,788 ) 39,192 Trade names and trademarks 4,900 (4,683 ) 217 MLOA lender licenses 400 (17 ) 383 Intangibles-in-progress 2,941 — 2,941 Total $ 290,527 $ (182,623 ) $ 107,904 December 31, 2017 Cost Accumulated Amortization Net Purchased content $ 35,260 $ (20,480 ) $ 14,780 Software 18,957 (8,899 ) 10,058 Customer relationships 103,900 (46,365 ) 57,535 Developed technology 113,380 (56,664 ) 56,716 Trade names and trademarks 4,900 (3,943 ) 957 Advertising relationships 9,000 (8,525 ) 475 Intangibles-in-progress 2,190 — 2,190 Total $ 287,587 $ (144,876 ) $ 142,711
Estimated Future Amortization Expense for Intangible Assets	Estimated future amortization expense for intangible assets, including amortization related to future commitments (see Note 19 ), as of December 31, 2018 is as follows (in thousands): 2019 $ 42,648 2020 39,420 2021 33,908 2022 5,480 2023 373 Total future amortization expense $ 121,829

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	12 Months Ended
	Dec. 31, 2018
Payables and Accruals [Abstract]
Summary of accrued expenses and other current liabilities	The following table presents the detail of accrued expenses and other current liabilities as of the dates presented (in thousands): December 31, 2018 2017 Accrued marketing and advertising $ 18,559 $ 17,180 Accrued purchased content 4,256 5,984 Accrued estimated legal liabilities and legal fees 7,305 9,052 Merger consideration payable to former stockholders of certain acquired entities 5,904 5,904 Other accrued expenses and other current liabilities 27,077 23,253 Total accrued expenses and other current liabilities $ 63,101 $ 61,373

Deferred Revenue (Tables)

Deferred Revenue (Tables)	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Schedule of Change in Deferred Revenue	The following table presents the change in deferred revenue for the period presented (in thousands): Year Ended December 31, 2018 Balance as of January 1, 2018 $ 31,918 Deferral of revenue 982,647 Less: Revenue recognized (980,485 ) Balance as of December 31, 2018 $ 34,080

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Outstanding Principal Amount and Carrying Value	The following table presents the outstanding principal amount and carrying value of the 2021 Notes as of the dates presented (in thousands): Outstanding Principal Amount Unamortized Debt Discount and Debt Issuance Costs Carrying Value December 31, 2018 $ 460,000 $ (65,355 ) $ 394,645 December 31, 2017 $ 460,000 $ (84,721 ) $ 375,279 Outstanding Principal Amount Unamortized Debt Discount and Debt Issuance Costs Carrying Value December 31, 2018 $ 373,750 $ (79,012 ) $ 294,738

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Components of Income Tax (Benefit) Expense	The following table summarizes the components of our income tax (benefit) expense for the periods presented (in thousands): Year Ended December 31, 2018 2017 2016 Current income tax expense Foreign $ 161 $ — $ — Total current income tax expense 161 — — Deferred income tax (benefit) expense Federal (28,502 ) (84,238 ) (1,248 ) State (2,441 ) (5,348 ) 1,378 Foreign (320 ) — — Total deferred income tax (benefit) expense (31,263 ) (89,586 ) 130 Total income tax (benefit) expense $ (31,102 ) $ (89,586 ) $ 130
Reconciliation of Federal Statutory Rate and Effective Tax Rate	The following table presents a reconciliation of the federal statutory rate and our effective tax rate for the periods presented: Year Ended December 31, 2018 2017 2016 Tax expense at federal statutory rate (21.0 )% (35.0 )% (35.0 )% State income taxes, net of federal tax benefit (5.9 ) (4.4 ) (1.9 ) Nondeductible expenses — 0.8 4.9 Share-based compensation (16.5 ) (20.6 ) (0.2 ) IRC section 162(m) 1.0 — — Research and development credits (8.4 ) (6.3 ) (1.5 ) Meals and entertainment 1.8 — — Return to provision adjustments (4.2 ) — — Enactment of Tax Act (1.9 ) (13.1 ) — Other 0.4 2.2 (0.9 ) Valuation allowance 34.0 27.7 34.7 Effective tax rate (20.7 )% (48.7 )% 0.1 %
Deferred Tax Assets and Liabilities	The following table presents the significant components of our deferred tax assets and liabilities as of the dates presented (in thousands): December 31, 2018 2017 Deferred tax assets: Federal and state net operating loss carryforwards $ 259,629 $ 234,316 Share-based compensation 55,280 47,655 Start-up and organizational costs 99 146 Research and development credits 48,805 35,793 Other tax credits 910 910 Accruals and reserves 3,000 2,729 Deferred rent 4,842 5,484 Other deferred tax assets 14,267 8,342 Total deferred tax assets 386,832 335,375 Deferred tax liabilities: Website and software development costs (14,685 ) (13,202 ) Goodwill (598 ) (688 ) Intangible assets (45,035 ) (69,241 ) Discount on 2021 Notes and 2023 Notes not deductible for tax (31,450 ) (19,374 ) Depreciation and amortization (888 ) (2,425 ) Total deferred tax liabilities (92,656 ) (104,930 ) Net deferred tax assets before valuation allowance 294,176 230,445 Less: valuation allowance (307,599 ) (274,810 ) Net deferred tax liabilities $ (13,423 ) $ (44,365 )
Changes in Unrecognized Tax Benefits	Changes for unrecognized tax benefits for the periods presented are as follows (in thousands): Balance at January 1, 2016 $ 13,980 Gross increases—prior and current period tax positions 2,619 Gross decreases—prior period tax positions (1,204 ) Balance at December 31, 2016 $ 15,395 Gross increases—current period tax positions 5,216 Gross increases—prior period tax positions 1,002 Balance at December 31, 2017 $ 21,613 Gross increases—current period tax positions 6,421 Gross increases—prior period tax positions 591 Balance at December 31, 2018 $ 28,625

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Common and Capital Stock Reserved for Future Issuance	The following shares of common and capital stock have been reserved for future issuance as of the dates presented: December 31, 2018 December 31, 2017 Option awards outstanding 27,310,110 26,645,206 Restricted stock units outstanding 5,266,324 4,016,405 Class A common stock and Class C capital stock available for grant under 2011 Plan 3,675,082 5,076,898 Shares issuable upon conversion of outstanding Class B common stock 6,217,447 6,217,447 Total 42,468,963 41,955,956

Share-Based Awards (Tables)

Share-Based Awards (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Option Award and Stock Appreciation Rights Activity	The following table summarizes option award activity for the year ended December 31, 2018 : Number of Shares Subject to Existing Options Weighted- Average Exercise Price Per Share Weighted- Average Remaining Contractual Life (Years) Aggregate Intrinsic Value (in thousands) Outstanding at January 1, 2018 26,645,206 $ 27.70 5.72 $ 355,739 Granted 6,963,320 48.95 Exercised (5,472,728 ) 21.94 Forfeited or cancelled (825,688 ) 35.32 Outstanding at December 31, 2018 27,310,110 34.04 6.23 97,941 Vested and exercisable at December 31, 2018 15,287,932 29.73 4.72 75,867
Fair Value of Options Granted, Excluding Options Grant to Executives Estimated at Date of Grant Using Black Scholes Merton Option Pricing Model	The fair value of options granted is estimated at the date of grant using the Black-Scholes-Merton option-pricing model, assuming no dividends and with the following assumptions for the periods presented: Year Ended December 31, 2018 2017 2016 Expected volatility 42% – 45% 45% – 49% 49% – 51% Expected dividend yield — — — Risk-free interest rate 2.52% – 2.84% 1.67% – 2.06% 0.89% – 1.89% Weighted-average expected life 4.50 – 5.00 years 4.25 – 4.75 years 3.75 – 4.25 years Weighted-average fair value of options granted $19.11 $14.51 $9.42
Summary of Restricted Stock Units Activity	The following table summarizes activity for restricted stock units for the year ended December 31, 2018 : Restricted Stock Units Weighted- Average Grant- Date Fair Value Unvested outstanding at January 1, 2018 4,016,405 $ 33.22 Granted 3,725,726 48.26 Vested (1,740,134 ) 35.63 Forfeited or cancelled (735,673 ) 39.59 Unvested outstanding at December 31, 2018 5,266,324 42.19
Effects of Share Based Compensation in Consolidated Statements of Operations	The following table presents the effects of share-based compensation expense in our consolidated statements of operations during the periods presented (in thousands): Year Ended December 31, 2018 2017 2016 Cost of revenue $ 4,127 $ 3,884 $ 3,550 Sales and marketing 22,942 22,735 23,320 Technology and development 56,673 39,938 31,466 General and administrative 65,342 47,014 48,582 $ 149,084 $ 113,571 $ 106,918

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share	For the periods presented, the following Class A common stock and Class C capital stock equivalents were excluded from the calculations of diluted net loss per share because their effect would have been antidilutive (in thousands): Year Ended December 31, 2018 2017 2016 Weighted-average Class A common stock and Class C capital stock option awards outstanding 22,736 27,998 19,993 Weighted-average Class A common stock and Class C capital stock restricted stock units outstanding 4,949 4,262 3,607 Class A common stock issuable upon conversion of the 2020 Notes 400 435 440 Total Class A common stock and Class C capital stock equivalents 28,085 32,695 24,040

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Future Minimum Payments for All Operating Leases	Future minimum payments for all operating leases as of December 31, 2018 are as follows (in thousands): 2019 $ 29,085 2020 38,060 2021 40,099 2022 37,721 2023 36,458 All future years 85,462 Total future minimum lease payments $ 266,885
Purchase Commitments for Content Related to Mobile Applications and Websites	The amounts due for these non-cancelable purchase commitments and homes under contract as of December 31, 2018 are as follows (in thousands): Purchase Obligations Homes Under Contract 2019 $ 64,124 $ 88,943 2020 64,007 — 2021 32,735 — Total future purchase commitments $ 160,866 $ 88,943

Segment Information and Reven_2

Segment Information and Revenue (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Revenue Categories	This information is included in the following table for the period presented (in thousands): Year Ended December 31, 2018 IMT Homes Consolidated Revenue: Premier Agent $ 898,332 $ — $ 898,332 Rentals 134,587 — 134,587 Mortgages 80,046 — 80,046 Other 168,224 — 168,224 Homes — 52,365 52,365 Total revenue 1,281,189 52,365 1,333,554 Costs and expenses: Cost of revenue 104,330 49,260 153,590 Sales and marketing 534,038 18,583 552,621 Technology and development 389,539 21,279 410,818 General and administrative 238,727 23,426 262,153 Impairment costs 79,000 — 79,000 Acquisition-related costs 2,332 — 2,332 Integration costs 2,015 — 2,015 Total costs and expenses 1,349,981 112,548 1,462,529 Income (loss) from operations (68,792 ) (60,183 ) (128,975 ) Other income 19,270 — 19,270 Interest expense (39,078 ) (2,177 ) (41,255 ) Loss before income taxes $ (88,600 ) $ (62,360 ) $ (150,960 )

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019	Oct. 01, 2017
Schedule Of Significant Accounting Policies [Line Items]
Other than temporary impairment loss	$ 0	$ 0
Non-cash impairment of indefinite-lived intangible assets	79,000,000	174,000,000	$ 0
Research and development expenses	410,818,000	319,985,000	255,583,000
Advertising expenses	177,300,000	156,500,000	120,200,000
Accounting Standards Update 2016-02 | Scenario, Forecast | Subsequent Event
Schedule Of Significant Accounting Policies [Line Items]
Right-to-use assets				$ 90,000,000
Lease liability				$ 115,000,000
Technology and Development
Schedule Of Significant Accounting Policies [Line Items]
Research and development expenses	$ 298,100,000	193,000,000	$ 170,100,000
Purchased content
Schedule Of Significant Accounting Policies [Line Items]
Useful life of capitalized purchased content asset	5 years
Minimum | Software Development
Schedule Of Significant Accounting Policies [Line Items]
Expected useful lives	1 year
Maximum | Software Development
Schedule Of Significant Accounting Policies [Line Items]
Expected useful lives	3 years
Trulia
Schedule Of Significant Accounting Policies [Line Items]
Indefinite-lived intangible asset	$ 108,000,000	177,000,000			$ 351,000,000
Trulia | Trade names and trademarks
Schedule Of Significant Accounting Policies [Line Items]
Non-cash impairment of indefinite-lived intangible assets	$ 69,000,000	$ 174,000,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Useful Lives (Detail)	12 Months Ended
	Dec. 31, 2018
Minimum | Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment (useful life)	2 years
Minimum | Office equipment, furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment (useful life)	5 years
Maximum | Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment (useful life)	3 years
Maximum | Office equipment, furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment (useful life)	7 years

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Schedule of Application of Guidance (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Sales and marketing	$ 552,621	$ 448,201	$ 382,419
Total costs and expenses	1,462,529	1,238,668	1,039,443
Income (loss) from operations	(128,975)	(161,874)	(192,854)
Income (loss) before income taxes	(150,960)	(184,006)	(220,308)
Income tax benefit (expense)	31,102	89,586	(130)
Net loss	$ (119,858)	$ (94,420)	$ (220,438)
Net loss per share-basic and diluted (usd per share)	$ (0.61)	$ (0.51)	$ (1.22)
Statement of Financial Position [Abstract]
Contract cost assets	$ 45,819
Total assets	4,291,116	$ 3,230,517
Deferred tax liabilities and other long-term liabilities	17,474	44,561
Total liabilities	1,023,937	569,694
Accumulated deficit	(671,779)	(592,243)
Total shareholders’ equity	3,267,179	2,660,823	$ 2,533,587	$ 2,679,053
Total liabilities and shareholders’ equity	4,291,116	$ 3,230,517
Calculated under Revenue Guidance in Effect before Topic 606
Income Statement [Abstract]
Sales and marketing	558,118
Total costs and expenses	1,468,026
Income (loss) from operations	(134,472)
Income (loss) before income taxes	(156,457)
Income tax benefit (expense)	32,024
Net loss	$ (124,433)
Net loss per share-basic and diluted (usd per share)	$ (0.63)
Statement of Financial Position [Abstract]
Contract cost assets	$ 0
Total assets	4,245,297
Deferred tax liabilities and other long-term liabilities	16,552
Total liabilities	1,023,015
Accumulated deficit	(716,676)
Total shareholders’ equity	3,222,282
Total liabilities and shareholders’ equity	4,245,297
Difference between Revenue Guidance in Effect before and after Topic 606 | Revenue from Contracts with Customers
Income Statement [Abstract]
Sales and marketing	(5,497)
Total costs and expenses	(5,497)
Income (loss) from operations	5,497
Income (loss) before income taxes	5,497
Income tax benefit (expense)	(922)
Net loss	$ 4,575
Net loss per share-basic and diluted (usd per share)	$ 0.02
Statement of Financial Position [Abstract]
Contract cost assets	$ 45,819
Total assets	45,819
Deferred tax liabilities and other long-term liabilities	922
Total liabilities	922
Accumulated deficit	44,897
Total shareholders’ equity	44,897
Total liabilities and shareholders’ equity	$ 45,819

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value of Cash Equivalents and Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 903,867
Mortgage loans held for sale	35,409
Assets	1,485,572	$ 656,135
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale	0
Assets	541,575	233,508
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage loans held for sale	35,409
Assets	943,997	422,627
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	541,575	233,508
Money market funds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	541,575	233,508
Money market funds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	3,999	3,987
Short-term investments	85,506	39,325
Commercial paper | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Short-term investments	0	0
Commercial paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	3,999	3,987
Short-term investments	85,506	39,325
U.S. government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		1,748
Short-term investments	646,496	298,758
U.S. government agency securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		0
Short-term investments	0	0
U.S. government agency securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		1,748
Short-term investments	646,496	298,758
Corporate notes and bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		6,199
Short-term investments	112,933	44,607
Corporate notes and bonds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		0
Short-term investments	0	0
Corporate notes and bonds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		6,199
Short-term investments	112,933	44,607
Municipal securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	39,306	11,459
Municipal securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Municipal securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	39,306	11,459
Foreign government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	14,915	5,998
Foreign government securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Foreign government securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	14,915	5,998
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		249
Short-term investments	4,711	10,297
Certificates of deposit | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		0
Short-term investments	0	0
Certificates of deposit | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		249
Short-term investments	4,711	$ 10,297
Interest rate lock commitments | Not Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	847
Interest rate lock commitments | Level 1 | Not Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0
Interest rate lock commitments | Level 2 | Not Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	847
Forward contracts | Not Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	(125)
Forward contracts | Level 1 | Not Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0
Forward contracts | Level 2 | Not Designated as Hedging Instrument
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	$ (125)

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value	$ 0	$ 0
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	0	$ 0
Interest rate lock commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional amounts of hedging instruments	26,700,000
Forward contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional amounts of hedging instruments	$ 28,800,000

Cash and Cash Equivalents, Sh_3

Cash and Cash Equivalents, Short-term Investments and Restricted Cash - Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Market Value of Cash and Cash Equivalents and Short-term Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Cash and Cash Equivalents, at Carrying Value [Abstract]
Cash and cash equivalents	$ 651,058	$ 352,095
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	904,837
Gross Unrealized Gains	76	3
Gross Unrealized Losses	(1,046)
Estimated Fair Market Value	903,867
Restricted cash	12,385
Cash, cash equivalents, short-term investments, and restricted cash, amortized cost	1,568,280	763,686
Cash, cash equivalents, short-term investments, and restricted cash, gross unrealized losses		(1,150)
Cash, cash equivalents, short-term investments, and restricted cash, estimated fair market value	1,567,310	762,539
U.S. government agency securities
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	647,266	299,814
Gross Unrealized Gains	51	0
Gross Unrealized Losses	(821)	(1,056)
Estimated Fair Market Value	646,496	298,758
Corporate notes and bonds
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	113,109	44,661
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(177)	(55)
Estimated Fair Market Value	112,933	44,607
Commercial paper
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	85,506	39,325
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Market Value	85,506	39,325
Municipal securities
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	39,316	11,494
Gross Unrealized Gains	23	0
Gross Unrealized Losses	(33)	(35)
Estimated Fair Market Value	39,306	11,459
Certificates of deposit
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	4,711	10,296
Gross Unrealized Gains	1	2
Gross Unrealized Losses	(1)	(1)
Estimated Fair Market Value	4,711	10,297
Foreign government securities
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	14,929	6,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(14)	(2)
Estimated Fair Market Value	14,915	5,998
Cash
Cash and Cash Equivalents, at Carrying Value [Abstract]
Cash and cash equivalents	105,484	106,404
Money market funds
Cash and Cash Equivalents, at Carrying Value [Abstract]
Cash and cash equivalents	541,575	233,508
Commercial paper
Cash and Cash Equivalents, at Carrying Value [Abstract]
Cash and cash equivalents	$ 3,999	3,987
U.S. government agency securities
Cash and Cash Equivalents, at Carrying Value [Abstract]
Cash and cash equivalents		1,748
Corporate notes and bonds
Cash and Cash Equivalents, at Carrying Value [Abstract]
Cash and cash equivalents, at cost		6,200
Cash and cash equivalents, gross unrealized losses		(1)
Cash and cash equivalents		6,199
Certificates of deposit
Cash and Cash Equivalents, at Carrying Value [Abstract]
Cash and cash equivalents		$ 249

Cash and Cash Equivalents, Sh_4

Cash and Cash Equivalents, Short-term Investments and Restricted Cash - Available-for-Sale Investments by Contractual Maturity (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Cash and Cash Equivalents [Abstract]
Amortized Cost, Due in one year or less	$ 801,828
Amortized Cost, Due after one year through two years	103,009
Amortized Cost	904,837
Estimated Fair Market Value, Due in one year or less	800,827
Estimated Fair Market Value, Due after one year through two years	103,040
Total	$ 903,867

Accounts Receivable, Net - Acco

Accounts Receivable, Net - Accounts Receivable (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Receivables [Abstract]
Accounts receivable	$ 61,134	$ 51,334
Unbilled accounts receivable	9,787	8,403
Less: allowance for doubtful accounts	(4,838)	(5,341)	$ (1,337)	$ (3,378)
Accounts receivable, net	$ 66,083	$ 54,396

Accounts Receivable, Net - Allo

Accounts Receivable, Net - Allowance for Doubtful Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for doubtful accounts:
Balance, beginning of period	$ 5,341	$ 1,337	$ 3,378
Additions charged to expense	869	7,349	2,681
Less: write-offs, net of recoveries and other adjustments	(1,372)	(3,345)	(4,722)
Balance, end of period	$ 4,838	$ 5,341	$ 1,337

Inventory (Details)

Inventory (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Work-in-progress	$ 45,943	$ 0
Finished goods	116,886	0
Inventory	$ 162,829	$ 0

Contract Cost Assets (Details)

Contract Cost Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue from Contract with Customer [Abstract]
Contract cost assets	$ 45,819,000	$ 0
Impairment of contract cost assets	0
Amortization of contract cost assets	$ 36,013,000	$ 0	$ 0

Property and Equipment, Net - D

Property and Equipment, Net - Detail of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment	$ 305,927	$ 258,501
Less: accumulated amortization and depreciation	(170,755)	(146,230)
Property and equipment, net	135,172	112,271
Website development costs
Property, Plant and Equipment [Line Items]
Property and equipment	149,891	130,072
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment	22,477	30,071
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment	65,012	47,321
Construction-in-progress
Property, Plant and Equipment [Line Items]
Property and equipment	29,037	28,150
Office equipment, furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment	$ 39,510	$ 22,887

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Amortization and depreciation expense related to property and equipment other than website development costs	$ 19,500	$ 15,600	$ 13,500
Capitalization of website development costs	34,100	49,900	49,500
Amortization of website development costs and intangible assets included in technology and development	79,309	94,349	87,060
Technology and Development
Property, Plant and Equipment [Line Items]
Amortization of website development costs and intangible assets included in technology and development	50,800	54,300	47,000
Technology and Development | Software Development
Property, Plant and Equipment [Line Items]
Amortization of website development costs and intangible assets included in technology and development	$ 28,600	$ 40,000	$ 40,000

Acquisitions and Equity Inves_3

Acquisitions and Equity Investments - Additional Information (Detail) - USD ($)	Oct. 31, 2018	Sep. 06, 2017	Jan. 11, 2017	Feb. 22, 2016	Oct. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2017
Schedule of Equity Method Investments [Line Items]
Goodwill acquired						$ 53,831,000
Non-cash impairment charge						79,000,000
June 2017 Investment
Schedule of Equity Method Investments [Line Items]
Equity interest in privately held corporation						0		$ 10,000,000
Non-cash impairment charge						10,000,000
October 2016 Investment
Schedule of Equity Method Investments [Line Items]
Impairment loss						0
Upward adjustment						0
Downward adjustment						0
October 2016 Investment | Variable Interest Entity, Not Primary Beneficiary
Schedule of Equity Method Investments [Line Items]
Equity interest in privately held corporation					$ 10,000,000
Percentage of equity interest in privately held variable interest entity					10.00%
Maximum exposure to loss in variable interest entity						$ 10,000,000
Mortgage Lenders of America, L.L.C.
Schedule of Equity Method Investments [Line Items]
Business acquisition, purchase price	$ 66,700,000
Unaudited pro forma revenue						3.00%	5.00%
Intangible assets	$ 2,600,000
Graphic Language, Inc. - New Home Feed Business
Schedule of Equity Method Investments [Line Items]
Goodwill acquired		$ 3,600,000
Identifiable intangible asset acquired		$ 1,900,000
HREO
Schedule of Equity Method Investments [Line Items]
Goodwill acquired			$ 4,000,000
Intangible assets			2,100,000
Net liabilities acquired			$ 100,000
Naked Apartments Inc
Schedule of Equity Method Investments [Line Items]
Intangible assets				$ 3,700,000
Business acquisition purchase price in cash				$ 13,200,000

Acquisitions and Equity Inves_4

Acquisitions and Equity Investments - Purchase Price Allocation (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Oct. 31, 2018	Dec. 31, 2017	Feb. 22, 2016
Business Acquisition [Line Items]
Goodwill	$ 1,984,907		$ 1,931,076
Mortgage Lenders of America, L.L.C.
Business Acquisition [Line Items]
Cash and cash equivalents		$ 10,796
Restricted cash		753
Mortgage loans available for sale		34,248
Property, plant and equipment		1,315
Intangible assets		2,600
Goodwill		53,831
Other acquired assets		3,079
Accounts payable		(1,953)
Accrued expenses		(2,591)
Warehouse lines of credit		(32,536)
Other assumed liabilities		(2,855)
Total purchase price		$ 66,687
Naked Apartments Inc
Business Acquisition [Line Items]
Current assets				$ 371
Intangible assets				3,700
Goodwill				10,610
Current liabilities				(101)
Deferred tax liabilities				(1,416)
Total purchase price				$ 13,164

Goodwill - Change in Goodwill (

Goodwill - Change in Goodwill (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
Goodwill [Roll Forward]
Balance as of December 31, 2017	$ 1,931,076
Goodwill recorded in connection with acquisition of MLOA	53,831
Balance as of December 31, 2018	$ 1,984,907

Intangible Assets - Schedule of

Intangible Assets - Schedule of Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Cost	$ 290,527	$ 287,587
Accumulated Amortization	(182,623)	(144,876)
Net	107,904	142,711
Purchased content
Finite-Lived Intangible Assets [Line Items]
Cost	42,110	35,260
Accumulated Amortization	(30,477)	(20,480)
Net	11,633	14,780
Software
Finite-Lived Intangible Assets [Line Items]
Cost	24,296	18,957
Accumulated Amortization	(13,925)	(8,899)
Net	10,371	10,058
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Cost	103,900	103,900
Accumulated Amortization	(60,733)	(46,365)
Net	43,167	57,535
Developed technology
Finite-Lived Intangible Assets [Line Items]
Cost	111,980	113,380
Accumulated Amortization	(72,788)	(56,664)
Net	39,192	56,716
Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Cost	4,900	4,900
Accumulated Amortization	(4,683)	(3,943)
Net	217	957
Advertising relationships
Finite-Lived Intangible Assets [Line Items]
Cost		9,000
Accumulated Amortization		(8,525)
Net		475
MLOA lender licenses
Finite-Lived Intangible Assets [Line Items]
Cost	400
Accumulated Amortization	(17)
Net	383
Intangibles-in-progress
Finite-Lived Intangible Assets [Line Items]
Cost	2,941	2,190
Accumulated Amortization	0	0
Net	$ 2,941	$ 2,190

Intangible Assets - Additional

Intangible Assets - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 01, 2017
Finite-Lived Intangible Assets [Line Items]
Amortization of website development costs and intangible assets included in technology and development	$ 79,309	$ 94,349	$ 87,060
Non-cash impairment of indefinite-lived intangible assets	79,000	174,000	0
Trulia
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible asset	108,000	177,000		$ 351,000
Trulia | Trade names and trademarks
Finite-Lived Intangible Assets [Line Items]
Non-cash impairment of indefinite-lived intangible assets	69,000	174,000
Technology and Development
Finite-Lived Intangible Assets [Line Items]
Amortization of website development costs and intangible assets included in technology and development	$ 50,800	$ 54,300	$ 47,000

Intangible Assets - Estimated F

Intangible Assets - Estimated Future Amortization Expense for Intangible Assets (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2,019	$ 42,648
2,020	39,420
2,021	33,908
2,022	5,480
2,023	373
Total future amortization expense	$ 121,829

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued Expenses and Other Current Liabilities [Line Items]
Total accrued expenses and other current liabilities	$ 63,101	$ 61,373
Accrued marketing and advertising
Accrued Expenses and Other Current Liabilities [Line Items]
Total accrued expenses and other current liabilities	18,559	17,180
Accrued purchased content
Accrued Expenses and Other Current Liabilities [Line Items]
Total accrued expenses and other current liabilities	4,256	5,984
Accrued estimated legal liabilities and legal fees
Accrued Expenses and Other Current Liabilities [Line Items]
Total accrued expenses and other current liabilities	7,305	9,052
Merger consideration payable to former stockholders of certain acquired entities
Accrued Expenses and Other Current Liabilities [Line Items]
Total accrued expenses and other current liabilities	5,904	5,904
Other accrued expenses and other current liabilities
Accrued Expenses and Other Current Liabilities [Line Items]
Total accrued expenses and other current liabilities	$ 27,077	$ 23,253

Deferred Revenue (Details)

Deferred Revenue (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
Change in Contract with Customer, Liability [Roll Forward]
Balance as of January 1, 2018	$ 31,918
Deferral of revenue	982,647
Less: Revenue recognized	(980,485)
Balance as of December 31, 2018	34,080
Revenue recognized, recorded in deferred revenue as of prior period	$ 28,800

Debt - Additional Information (

Debt - Additional Information (Detail)	Jul. 31, 2018USD ($)	Jul. 03, 2018USD ($)d$ / shares	Dec. 12, 2016USD ($)d$ / shares	Dec. 31, 2016USD ($)	Jan. 31, 2015	Dec. 31, 2018USD ($)agreementd$ / shares	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2018USD ($)	Feb. 28, 2015USD ($)
Debt Instrument [Line Items]
Outstanding borrowings on revolving credit facility						$ 116,700,000	$ 0
Net proceeds used to purchase capped call confirmations						29,414,000	0	$ 36,616,000
Interest expense						41,255,000	27,517,000	7,408,000
Amortization of discount and issuance costs						26,672,000	18,012,000	883,000
Proceeds from issuance of Notes, net of issuance costs						364,020,000	0	447,784,000
Issuance of Convertible Senior notes, transaction costs				$ 2,494,000		2,047,000		2,494,000
Class C Capital Stock
Debt Instrument [Line Items]
Public offering price (usd per share) | $ / shares		$ 57
1.50% Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Equity component of convertible debt						78,600,000
Interest expense						10,100,000
Amortization of discount and issuance costs						7,300,000
Contractual coupon interest						$ 2,800,000
Effective interest rate						6.99%
Debt instrument amortization period						54 months
Debt instrument carrying value						$ 294,738,000
1.50% Convertible Senior Notes Due 2023 | Class C Capital Stock
Debt Instrument [Line Items]
Conversion price (usd per share) | $ / shares						$ 78.37
1.50% Convertible Senior Notes Due 2023 | Fair Value, Inputs, Level 3
Debt Instrument [Line Items]
Fair value of convertible notes						$ 321,900,000
1.50% Convertible Senior Notes Due 2023 | Convertible Debt
Debt Instrument [Line Items]
Debt instrument, interest rate stated percentage		1.50%
Debt instrument, principal amount issued		$ 373,800,000
Net proceeds from issuance		364,000,000
Net proceeds used to purchase capped call confirmations		$ 29,400,000
Debt instrument, conversion rate shares		0.0127592
Conversion price (usd per share) | $ / shares		$ 78.37
Debt instrument, convertible threshold percentage		130.00%
Debt instrument, convertible threshold trading days | d		20
Debt instrument, threshold consecutive trading days | d		30
Initial cap price (usd per share) | $ / shares		$ 105.45
Capped call confirmation premium percentage		85.00%
1.50% Convertible Senior Notes Due 2023 | Convertible Debt | Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Repurchase price percentage of principal amount		100.00%
1.50% Convertible Senior Notes Due 2023 | Convertible Debt | Debt Instrument, Redemption, Period Two
Debt Instrument [Line Items]
Repurchase price percentage of principal amount		100.00%
1.50% Convertible Senior Notes due 2023, Over-Allotment Option | Convertible Debt
Debt Instrument [Line Items]
Debt instrument, principal amount issued		$ 48,800,000
2.00% Convertible Senior Notes Due 2021
Debt Instrument [Line Items]
Debt instrument, interest rate stated percentage			2.00%
Debt instrument, principal amount issued			$ 460,000,000
Net proceeds used to purchase capped call confirmations			$ 36,600,000
Repurchase price percentage of principal amount			100.00%
Interest expense						28,600,000	27,200,000	1,300,000
Amortization of discount and issuance costs						19,400,000	18,000,000	900,000
Contractual coupon interest						$ 9,200,000	$ 9,200,000	$ 500,000
Effective interest rate				7.44%		7.44%	7.44%	7.44%
Debt instrument amortization period						35 months
Initial cap price (usd per share) | $ / shares						$ 69.19
Capped call confirmation premium percentage						85.00%
Proceeds from issuance of Notes, net of issuance costs			$ 447,800,000
Partial repurchase of Notes				$ 370,200,000
Equity component of issuance of 2021 Notes			91,400,000
Issuance of Convertible Senior notes, transaction costs			12,200,000
Amount of fees paid			$ 11,500,000
Accrued interest						$ 800,000	$ 800,000
Debt instrument carrying value						$ 394,645,000	375,279,000
2.00% Convertible Senior Notes Due 2021 | Class C Capital Stock
Debt Instrument [Line Items]
Debt instrument, conversion rate shares						0.0190985
Conversion price (usd per share) | $ / shares			$ 52.36			$ 52.36
Debt instrument, convertible threshold percentage			130.00%
Debt instrument, convertible threshold trading days | d			20
Debt instrument, threshold consecutive trading days | d			30
2.00% Convertible Senior Notes Due 2021 | Fair Value, Inputs, Level 3
Debt Instrument [Line Items]
Fair value of convertible notes						$ 446,200,000	509,000,000
2.00% Convertible Senior Notes Due 2021, Over-Allotment Option
Debt Instrument [Line Items]
Debt instrument, principal amount issued			$ 60,000,000
2.75% Convertible Senior Notes Due 2020
Debt Instrument [Line Items]
Debt instrument, interest rate stated percentage						2.75%
Debt instrument, conversion rate shares					0.0278303
Repurchase price percentage of principal amount						100.00%
Interest expense						$ 300,000	300,000	$ 6,100,000
Debt repurchase aggregate principal amount				$ 219,900,000				$ 219,900,000
Debt instrument carrying value						$ 9,600,000	10,100,000			$ 230,000,000
2.75% Convertible Senior Notes Due 2020 | Class A Common Stock
Debt Instrument [Line Items]
Debt instrument, convertible threshold percentage						130.00%
Debt instrument, convertible threshold trading days | d						20
Debt instrument, threshold consecutive trading days | d						30
2.75% Convertible Senior Notes Due 2020 | Class C Common Stock Distribution | Class A Common Stock
Debt Instrument [Line Items]
Debt instrument, conversion rate shares						0.0414550
Conversion price (usd per share) | $ / shares						$ 24.12
2.75% Convertible Senior Notes Due 2020 | Fair Value, Inputs, Level 3
Debt Instrument [Line Items]
Fair value of convertible notes						$ 16,700,000	$ 17,600,000
Mortgage Lenders of America, L.L.C.
Debt Instrument [Line Items]
Number of warehouse lines of credit | agreement						2
Trulia Merger Agreement | 2.75% Convertible Senior Notes Due 2020 | Class A Common Stock
Debt Instrument [Line Items]
Debt instrument, conversion rate shares						0.0123567
Conversion price (usd per share) | $ / shares						$ 80.93
Common stock exchange ratio						0.444
Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity						$ 500,000,000
Current borrowing capacity									$ 126,700,000
Revolving credit facility, initial term	1 year
Revolving credit facility, extension of initial term	2 years
Availability limit, acquisition cost of residential property	85.00%
Availability limit, market value of residential property	85.00%
Amount available for future borrowings						$ 383,300,000
Weighted average interest rate						5.86%
Revolving Credit Facility | Credit Suisse AG, Cayman Islands Branch
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 250,000,000					$ 500,000,000
Line of Credit | Warehouse Lines of Credit, due July 2019
Debt Instrument [Line Items]
Maximum borrowing capacity						50,000,000
Line of Credit | Mortgage Lenders of America, L.L.C. | Warehouse Lines of Credit, due March 2019
Debt Instrument [Line Items]
Maximum borrowing capacity						$ 50,000,000
Weighted average interest rate						4.88%
Line of Credit | Mortgage Lenders of America, L.L.C. | Warehouse Lines of Credit, due July 2019
Debt Instrument [Line Items]
Weighted average interest rate						4.73%
Line of Credit | Mortgage Lenders of America, L.L.C. | Warehouse Lines of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity						$ 100,000,000

Debt - Outstanding Principal Am

Debt - Outstanding Principal Amount and Carrying Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
1.50% Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Outstanding Principal Amount	$ 373,750
Unamortized Debt Discount and Debt Issuance Costs	(79,012)
Carrying Value	294,738
2.00% Convertible Senior Notes Due 2021
Debt Instrument [Line Items]
Outstanding Principal Amount	460,000	$ 460,000
Unamortized Debt Discount and Debt Issuance Costs	(65,355)	(84,721)
Carrying Value	$ 394,645	$ 375,279

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 28, 2015
Schedule Of Income Tax [Line Items]
Income tax (benefit) expense	$ 31,102	$ 89,586	$ (130)
Effective tax rate	20.70%	48.70%	(0.10%)
Adjustment to income tax (benefit) under the Tax Act	$ (5,900)
Non-cash impairment of indefinite-lived intangible assets	79,000	$ 174,000	$ 0
Income tax benefit, Tax Cuts and Jobs Act, reduction in net deferred tax liability		23,600
Increase/decrease in valuation allowance	32,800	57,500
Unrecognized tax benefits	28,625	21,613	$ 15,395	$ 13,980
Unrecognized income tax accrued interest and penalties	0
Research and Development
Schedule Of Income Tax [Line Items]
Net operating loss carryforwards	$ 48,800	35,800
Tax credit carryforwards expiration year	2,025
Trulia
Schedule Of Income Tax [Line Items]
Income tax (benefit) expense	$ 15,400	66,000
Trade names and trademarks | Trulia
Schedule Of Income Tax [Line Items]
Non-cash impairment of indefinite-lived intangible assets	69,000	174,000
Indefinite-lived intangible asset					$ 351,000
Federal
Schedule Of Income Tax [Line Items]
Net operating loss carryforwards	1,081,700	1,014,000
State
Schedule Of Income Tax [Line Items]
Net operating loss carryforwards	$ 32,500	$ 21,400

Income Taxes - Components of In

Income Taxes - Components of Income Tax (Benefit) Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current income tax expense
Foreign	$ 161	$ 0	$ 0
Total current income tax expense	161	0	0
Deferred income tax (benefit) expense
Federal	(28,502)	(84,238)	(1,248)
State	(2,441)	(5,348)	1,378
Foreign	(320)	0	0
Total deferred income tax (benefit) expense	(31,263)	(89,586)	130
Total income tax (benefit) expense	$ (31,102)	$ (89,586)	$ 130

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Federal Statutory Rate and Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Tax expense at federal statutory rate	(21.00%)	(35.00%)	(35.00%)
State income taxes, net of federal tax benefit	(5.90%)	(4.40%)	(1.90%)
Nondeductible expenses	0.00%	0.80%	4.90%
Share-based compensation	(16.50%)	(20.60%)	(0.20%)
IRC section 162(m)	1.00%	0.00%	0.00%
Research and development credits	(8.40%)	(6.30%)	(1.50%)
Meals and entertainment	1.80%	0.00%	0.00%
Return to provision adjustments	(4.20%)	0.00%	0.00%
Enactment of Tax Act	(1.90%)	(13.10%)	0.00%
Other	0.40%	2.20%	(0.90%)
Valuation allowance	34.00%	27.70%	34.70%
Effective tax rate	(20.70%)	(48.70%)	0.10%

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Federal and state net operating loss carryforwards	$ 259,629	$ 234,316
Share-based compensation	55,280	47,655
Start-up and organizational costs	99	146
Research and development credits	48,805	35,793
Other tax credits	910	910
Accruals and reserves	3,000	2,729
Deferred rent	4,842	5,484
Other deferred tax assets	14,267	8,342
Total deferred tax assets	386,832	335,375
Deferred tax liabilities:
Website and software development costs	(14,685)	(13,202)
Goodwill	(598)	(688)
Intangible assets	(45,035)	(69,241)
Discount on 2021 Notes and 2023 Notes not deductible for tax	(31,450)	(19,374)
Depreciation and amortization	(888)	(2,425)
Total deferred tax liabilities	(92,656)	(104,930)
Net deferred tax assets before valuation allowance	294,176	230,445
Less: valuation allowance	(307,599)	(274,810)
Net deferred tax liabilities	$ (13,423)	$ (44,365)

Income Taxes - Changes in Unrec

Income Taxes - Changes in Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits beginning balance	$ 21,613	$ 15,395	$ 13,980
Gross increases - prior and current period tax positions			2,619
Gross decreases - prior period tax positions			(1,204)
Gross increases - current period tax positions	6,421	5,216
Gross increases - prior period tax positions	591	1,002
Unrecognized tax benefits ending balance	$ 28,625	$ 21,613	$ 15,395

Shareholders' Equity - Addition

Shareholders' Equity - Additional Information (Detail) $ / shares in Units, $ in Millions	Jul. 03, 2018USD ($)$ / sharesshares	Dec. 31, 2018Voteshares	Dec. 31, 2017shares	Dec. 31, 2016shares
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)		0	0
Preferred stock, shares outstanding (in shares)		0	0
Class A Common Stock
Class of Stock [Line Items]
Common stock holders voting right | Vote		1
Conversion of common stock conversion ratio		1
Number of common stock issued		0	0	0
Class B Common Stock
Class of Stock [Line Items]
Common stock holders voting right | Vote		10
Number of common stock converted		0	0	0
Class C Capital Stock
Class of Stock [Line Items]
Common stock holders voting right | Vote		0
Public offering price (usd per share) | $ / shares	$ 57
Net proceeds from public offering | $	$ 360.3
Public Stock Offering | Class C Capital Stock
Class of Stock [Line Items]
Shares issued and sold (in shares)	6,557,017
Over-Allotment Option | Class C Capital Stock
Class of Stock [Line Items]
Shares issued and sold (in shares)	855,263

Shareholders' Equity - Common a

Shareholders' Equity - Common and Capital Stock Reserved for Future Issuance (Detail) - shares	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Options and Stock Appreciation Rights Outstanding (in shares)		26,645,206
Total (in shares)	42,468,963	41,955,956
Class B Common Stock
Class of Stock [Line Items]
Shares issuable upon conversion of outstanding Class B common stock (in shares)	6,217,447	6,217,447
Option Awards
Class of Stock [Line Items]
Options and Stock Appreciation Rights Outstanding (in shares)	27,310,110
Option awards outstanding (in shares)		26,645,206
Option Awards | 2011 Plan
Class of Stock [Line Items]
Class A common stock and Class C capital stock available for grant under 2011 Plan (in shares)	3,675,082	5,076,898
Restricted Stock Units
Class of Stock [Line Items]
Unvested amount (in shares)	5,266,324	4,016,405
Restricted stock units outstanding (in shares)		4,016,405

Share-Based Awards - Zillow Gro

Share-Based Awards - Zillow Group, Inc. Incentive Plan - Additional Information (Detail) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares)	42,468,963	41,955,956
Amended and Restated 2011 Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares)	18,400,000
Increase in number of shares of common and capital stock available for issuance percentage	3.50%
Increase in number of shares of common and capital stock available for issuance	10,500,000
2011 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price per share fixed	100.00%
2011 Plan | Option Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement by share based payment, award minimum exercisable period	3 months
Share based compensation arrangement by share based payment, award maximum exercisable period	12 months
2011 Plan | Option Awards | Vesting After 12 Months
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	25.00%
Vesting period	12 months
2011 Plan | Option Awards | Vesting After 36 Months
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	36 months
2011 Plan | Option Awards | Quarterly Vesting Over 4 Years
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
2011 Plan | Option Awards | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	7 years
2011 Plan | Option Awards | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
2011 Plan | Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	25.00%
2011 Plan | Restricted Stock Units | Vesting After 12 Months
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
2011 Plan | Restricted Stock Units | Vesting After 36 Months
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	12.50%
2011 Plan | Restricted Stock Units | Minimum | Vesting After 12 Months
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	12 months
2011 Plan | Restricted Stock Units | Minimum | Vesting After 36 Months
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	6 months
2011 Plan | Restricted Stock Units | Maximum | Vesting After 12 Months
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
2011 Plan | Restricted Stock Units | Maximum | Vesting After 36 Months
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years 6 months

Share-Based Awards - Trulia Sto

Share-Based Awards - Trulia Stock Incentive Plan - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018
Trulia 2012 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
Exercise price per share fixed	100.00%
Trulia 2005 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
Trulia 2005 Stock Incentive Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	12 months
Trulia 2005 Stock Incentive Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	36 months
Trulia 2005 Stock Incentive Plan | Vesting After 12 Months
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	25.00%
Trulia 2005 Stock Incentive Plan | Monthly Vesting Over Two to Four Years | Minimum | Option Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	2 years
Trulia 2005 Stock Incentive Plan | Monthly Vesting Over Two to Four Years | Maximum | Option Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years

Share-Based Awards - Summary of

Share-Based Awards - Summary of Option Award and Stock Appreciation Rights Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Number of Shares Subject to Existing Options
Number of Shares Subject to Existing Option Awards and Stock Appreciation Rights, Beginning Balance (in shares)	26,645,206
Number of Shares Subject to Existing Option Awards and Stock Appreciation Rights, Granted (in shares)	6,963,320
Number of Shares Subject to Existing Option Awards and Stock Appreciation Rights, Exercised (in shares)	(5,472,728)
Number of Shares Subject to Existing Option Awards and Stock Appreciation Rights, Forfeited or cancelled (in shares)	(825,688)
Number of Shares Subject to Existing Option Awards and Stock Appreciation Rights, Ending Balance (in shares)		26,645,206
Number of Shares Subject to Existing Option Awards and Stock Appreciation Rights, Vested and exercisable, Ending balance (in shares)	15,287,932
Weighted- Average Exercise Price Per Share
Weighted-Average Exercise Price Per Share, Beginning Balance (usd per share)	$ 27.70
Weighted-Average Exercise Price Per Share, Granted (usd per share)	48.95
Weighted-Average Exercise Price Per Share, Exercised (usd per share)	21.94
Weighted-Average Exercise Price Per Share, Forfeited or cancelled (usd per share)	35.32
Weighted-Average Exercise Price Per Share, Ending Balance (usd per share)	34.04	$ 27.70
Weighted-Average Exercise Price Per Share, Vested and exercisable (usd per share)	$ 29.73
Weighted- Average Remaining Contractual Life (Years)
Weighted-Average Remaining Contractual Life (Years)	6 years 2 months 23 days	5 years 8 months 19 days
Weighted-Average Remaining Contractual Life (Years), Vested and exercisable	4 years 8 months 19 days
Aggregate Intrinsic Value (in thousands)
Aggregate Intrinsic Value	$ 97,941	$ 355,739
Aggregate Intrinsic Value Vested, and exercisable	$ 75,867

Share-Based Awards - Fair Value

Share-Based Awards - Fair Value of Options Granted, Excluding Options Grant to Executives Estimated at Date of Grant Using Black Scholes Merton Option Pricing Model (Detail) - Option Awards - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, minimum	42.00%	45.00%	49.00%
Expected volatility, maximum	45.00%	49.00%	51.00%
Expected dividend yield	0.00%	0.00%	0.00%
Risk-free interest rate, minimum	2.52%	1.67%	0.89%
Risk-free interest rate, maximum	2.84%	2.06%	1.89%
Weighted-average fair value of options granted (usd per share)	$ 19.11	$ 14.51	$ 9.42
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average expected life	4 years 6 months	4 years 3 months	3 years 9 months
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average expected life	5 years	4 years 9 months	4 years 3 months

Share-Based Awards - Option Awa

Share-Based Awards - Option Awards and Stock Appreciation Rights - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, option awards, exercises in period, total intrinsic value	$ 161.4	$ 156.1	$ 51.7
Stock Option and Stock Appreciation Rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized cost of unvested share-based compensation awards	$ 176.7
Unrecognized compensation cost expected recognition period	2 years 8 months 12 days
Option Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of options	$ 87.7	84.8	87.9
Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total fair value of awards vested	$ 87.7	$ 84.8	$ 87.9

Share-Based Awards - Summary _2

Share-Based Awards - Summary of Restricted Stock Units Activity (Detail) - Restricted Stock Units	12 Months Ended
	Dec. 31, 2018$ / sharesshares
Restricted Stock Units
Unvested outstanding, beginning balance (in shares) | shares	4,016,405
Granted (in shares) | shares	3,725,726
Vested (in shares) | shares	(1,740,134)
Forfeited or cancelled (in shares) | shares	(735,673)
Unvested outstanding, ending balance (in shares) | shares	5,266,324
Weighted-Average Grant-Date Fair Value
Unvested outstanding, beginning balance (usd per share) | $ / shares	$ 33.22
Granted (usd per share) | $ / shares	48.26
Vested (usd per share) | $ / shares	35.63
Forfeited or cancelled (usd per share) | $ / shares	39.59
Unvested outstanding, ending balance (usd per share) | $ / shares	$ 42.19

Share-Based Awards - Restricted

Share-Based Awards - Restricted Stock Units - Additional Information (Detail) - Restricted Stock Units - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total fair value of restricted stock vested	$ 62	$ 43.7	$ 46.5
Total unrecognized compensation cost	$ 204.9
Unrecognized compensation cost expected recognition period	2 years 10 months 24 days

Share-Based Awards - Effects of

Share-Based Awards - Effects of Share Based Compensation in Consolidated Statements of Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation	$ 149,084	$ 113,571	$ 106,918
Cost of Revenue
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation	4,127	3,884	3,550
Sales and Marketing
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation	22,942	22,735	23,320
Technology and Development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation	56,673	39,938	31,466
General and Administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation	$ 65,342	$ 47,014	$ 48,582

Net Loss Per Share - Additional

Net Loss Per Share - Additional Information (Detail) - $ / shares shares in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 12, 2016
2.00% Convertible Senior Notes Due 2021
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Conversion spread, shares	8.8
2.00% Convertible Senior Notes Due 2021 | Class C Capital Stock
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Conversion price (usd per share)	$ 52.36	$ 52.36
1.50% Convertible Senior Notes Due 2023
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Conversion spread, shares	4.8
1.50% Convertible Senior Notes Due 2023 | Class C Capital Stock
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Conversion price (usd per share)	$ 78.37

Net Loss Per Share - Antidiluti

Net Loss Per Share - Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class A Common Stock and Class C Capital Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total Class A common stock and Class C capital stock equivalents (in shares)	28,085	32,695	24,040
Class A Common Stock and Class C Capital Stock | Option Awards | Weighted Average
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total Class A common stock and Class C capital stock equivalents (in shares)	22,736	27,998	19,993
Class A Common Stock and Class C Capital Stock | Restricted Stock Awards and Restricted Stock Units | Weighted Average
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total Class A common stock and Class C capital stock equivalents (in shares)	4,949	4,262	3,607
Class A Common Stock | 2.75% Convertible Senior Notes Due 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total Class A common stock and Class C capital stock equivalents (in shares)	400	435	440

Commitments and Contingencies -

Commitments and Contingencies - Future Minimum Payments for All Operating Leases (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,019	$ 29,085
2,020	38,060
2,021	40,099
2,022	37,721
2,023	36,458
All future years	85,462
Total future minimum lease payments	$ 266,885

Commitments and Contingencies_2

Commitments and Contingencies - Additional Information (Detail)	Jun. 20, 2017USD ($)	Feb. 09, 2017USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Feb. 28, 2018claim	Sep. 30, 2017claim
Other Commitments [Line Items]
Rent expense			$ 23,700,000	$ 21,400,000	$ 16,600,000
Non-cancelable purchase commitments			160,866,000
Outstanding surety bonds			8,900,000	3,700,000
VHT Vs Zillow Group Inc
Other Commitments [Line Items]
Jury awarded damages	$ 4,100,000	$ 79,875
Estimated immaterial liability in general and administrative expenses			$ 4,100,000	$ 4,100,000
VHT Vs Zillow Group Inc | Statutory Damages
Other Commitments [Line Items]
Jury awarded damages		$ 8,200,000
Class Action Lawsuits
Other Commitments [Line Items]
Number of pending claims | claim							2
Shareholder Derivative Lawsuits
Other Commitments [Line Items]
Number of pending claims | claim						4

Commitments and Contingencies_3

Commitments and Contingencies - Purchase Commitments for Content Related to Mobile Applications and Websites (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Purchase Obligations
2,019	$ 64,124
2,020	64,007
2,021	32,735
Total future purchase commitments	160,866
Homes Under Contract
Purchase Obligations
2,019	88,943
2,020	0
2,021	0
Total future purchase commitments	$ 88,943

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended
	Apr. 30, 2016	Feb. 29, 2016
Mr.Lloyd Frink
Related Party Transaction [Line Items]
Reimbursement of costs incurred		$ 0.2
Mr.Richard Barton
Related Party Transaction [Line Items]
Reimbursement of costs incurred	$ 0.1	$ 0.2

Self-Insurance - Additional Inf

Self-Insurance - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Insurance [Line Items]
Minimum amount of individual claim under self insurance plan	$ 150,000
Liability for self-insured claims included in accrued compensation and benefits	$ 3,900,000	$ 2,000,000
Minimum
Insurance [Line Items]
Percentage of cumulative medical claim under self insurance plan	125.00%
Maximum
Insurance [Line Items]
Cumulative medical claim under self-insurance plan amount	$ 1,000,000

Employee Benefit Plan - Additio

Employee Benefit Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Plan Disclosure [Line Items]
Company's expense related to its defined contribution 401(k) retirement plans	$ 16	$ 12.3	$ 10.1
Maximum | Zillow Merger
Defined Contribution Plan Disclosure [Line Items]
Company's contribution based on employee contribution	4.00%

Segment Information and Reven_3

Segment Information and Revenue - Additional Information (Detail) - segment	9 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting [Abstract]
Number of operating segments	2		1
Number of reportable segments	2	1

Segment Information and Reven_4

Segment Information and Revenue - Revenue Categories (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue:
Total revenue	$ 1,333,554	$ 1,076,794	$ 846,589
Costs and Expenses [Abstract]
Cost of revenue	153,590
Sales and marketing	552,621	448,201	382,419
Technology and development	410,818	319,985	255,583
General and administrative	262,153	210,816	332,007
Impairment costs	79,000
Acquisition-related costs	2,332	463	1,423
Integration costs	2,015	0	0
Total costs and expenses	1,462,529	1,238,668	1,039,443
Loss from operations	(128,975)	(161,874)	(192,854)
Other income	19,270	5,385	2,711
Interest expense	(41,255)	(27,517)	(7,408)
Loss before income taxes	(150,960)	$ (184,006)	$ (220,308)
Premier Agent
Revenue:
Total revenue	898,332
Rentals
Revenue:
Total revenue	134,587
Mortgages
Revenue:
Total revenue	80,046
Other
Revenue:
Total revenue	168,224
Homes
Revenue:
Total revenue	52,365
IMT
Revenue:
Total revenue	1,281,189
Costs and Expenses [Abstract]
Cost of revenue	104,330
Sales and marketing	534,038
Technology and development	389,539
General and administrative	238,727
Impairment costs	79,000
Acquisition-related costs	2,332
Integration costs	2,015
Total costs and expenses	1,349,981
Loss from operations	(68,792)
Other income	19,270
Interest expense	(39,078)
Loss before income taxes	(88,600)
IMT | Premier Agent
Revenue:
Total revenue	898,332
IMT | Rentals
Revenue:
Total revenue	134,587
IMT | Mortgages
Revenue:
Total revenue	80,046
IMT | Other
Revenue:
Total revenue	168,224
IMT | Homes
Revenue:
Total revenue	0
Homes
Revenue:
Total revenue	52,365
Costs and Expenses [Abstract]
Cost of revenue	49,260
Sales and marketing	18,583
Technology and development	21,279
General and administrative	23,426
Impairment costs	0
Acquisition-related costs	0
Integration costs	0
Total costs and expenses	112,548
Loss from operations	(60,183)
Other income	0
Interest expense	(2,177)
Loss before income taxes	(62,360)
Homes | Premier Agent
Revenue:
Total revenue	0
Homes | Rentals
Revenue:
Total revenue	0
Homes | Mortgages
Revenue:
Total revenue	0
Homes | Other
Revenue:
Total revenue	0
Homes | Homes
Revenue:
Total revenue	$ 52,365

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - Revolving Credit Facility - USD ($)	Jan. 31, 2019	Dec. 31, 2018
Subsequent Event [Line Items]
Maximum borrowing capacity		$ 500,000,000
Subsequent Event | Credit Agreement | Citibank, N.A.
Subsequent Event [Line Items]
Maximum borrowing capacity	$ 500,000,000
Initial borrowing capacity	$ 50,000,000
Initial credit agreement term	2 years
Option to extend, term	1 year

Uncategorized Items - q42018for

Label	Element	Value
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 40,322,000
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	0
Additional Paid-in Capital [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	780,000
Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	40,322,000
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ (780,000)