Zulily (ZU) 10-K 24 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information Document (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 28, 2014	Jun. 29, 2014	Feb. 20, 2015
Entity Information [Line Items]
Entity Registrant Name	zulily, inc.
Entity Central Index Key	1478484
Current Fiscal Year End Date	-16
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	28-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Amendment Flag	FALSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float		$1,594,631,642
Common Class A [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding			68,345,478
Common Class B [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding			56,644,920

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 28, 2014	Dec. 29, 2013
In Thousands, unless otherwise specified
CURRENT ASSETS:
Cash and cash equivalents	$242,292	$290,089
Short-term investments	131,528	18,014
Accounts receivable	8,342	5,176
Inventories	17,373	12,979
Prepaid expenses and other current assets	8,165	4,192
Deferred income taxes — Net	4,449	0
Total current assets	412,149	330,450
PROPERTY AND EQUIPMENT — Net	78,898	24,613
OTHER NON-CURRENT ASSETS	1,331	1,024
Total assets	492,378	356,087
CURRENT LIABILITIES:
Accounts payable	109,267	55,607
Accrued expenses	39,474	30,773
Deferred revenue	44,243	23,250
Total current liabilities	192,984	109,630
DEFERRED INCOME TAXES — Net	5,012	0
OTHER NON-CURRENT LIABILITIES	18,419	4,254
Total liabilities	216,415	113,884
COMMITMENTS AND CONTINGENCIES (Note 5)
STOCKHOLDERS’ EQUITY
Preferred stock, $0.0001 par value—2,000,000 shares authorized as of December 28, 2014 and December 29, 2013, respectively; zero shares issued and outstanding as of December 28, 2014 and December 29, 2013	0	0
Additional paid-in capital	306,197	287,385
Accumulated other comprehensive loss	-3	-58
Accumulated deficit	-30,244	-45,136
Total stockholders’ equity	275,963	242,203
Total liabilities, preferred stock, and stockholders' equity	492,378	356,087
Common Class A [Member]
STOCKHOLDERS’ EQUITY
Common Stock, Value, Issued	6	1
Common Class B [Member]
STOCKHOLDERS’ EQUITY
Common Stock, Value, Issued	$7	$11

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets - Parenthetical (USD $)	Dec. 28, 2014	Dec. 29, 2013
Preferred stock, par value (in usd per share)	$0.00	$0.00
Preferred stock, shares authorized (in shares)	2,000,000	2,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common Class A [Member]
Common stock, par value (in usd per share)	$0.00	$0.00
Common stock, shares authorized (in shares)	500,000,000	500,000,000
Common stock, shares issued (in shares)	61,327,351	13,225,000
Common stock, shares outstanding (in shares)	61,327,351	13,225,000
Common Class B [Member]
Common stock, par value (in usd per share)	$0.00	$0.00
Common stock, shares authorized (in shares)	275,000,000	275,000,000
Common stock, shares issued (in shares)	64,115,226	110,159,235
Common stock, shares outstanding (in shares)	64,115,226	110,159,235
Common stock, shares subject to repurchase (in shares)	0	82,682

Consolidated_Statements_of_Ope

Consolidated Statements of Operations (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
Income Statement [Abstract]
NET SALES	$1,200,079	$695,709	$331,240
COST OF SALES	875,633	502,318	240,943
GROSS PROFIT	324,446	193,391	90,297
OPERATING EXPENSES:
Marketing	100,730	59,667	37,780
Selling, general, and administrative	207,986	120,695	63,071
TOTAL OPERATING EXPENSES	308,716	180,362	100,851
INCOME (LOSS) FROM OPERATIONS	15,730	13,029	-10,554
INTEREST INCOME (EXPENSE)—Net	317	136	43
OTHER INCOME (EXPENSE)—Net	-46	99	176
NET INCOME (LOSS) BEFORE PROVISION FOR INCOME TAXES	16,001	13,264	-10,335
PROVISION FOR INCOME TAXES	1,109	356	0
NET INCOME (LOSS)	14,892	12,908	-10,335
Net income (loss) attributable to Class A and Class B common stockholders	$14,892	$0	($46,822)
Net income (loss) per share attributable to Class A and Class B common stockholders:
Basic (in dollars per share)	$0.12	$0	($1.23)
Diluted (in dollars per share)	$0.11	$0	($1.23)
Weighted average shares outstanding used to compute net income (loss) per share attributable to Class A and Class B common stockholders:
Basic (in shares)	124,679,716	59,450,186	37,976,724
Diluted (in shares)	132,317,357	59,450,186	37,976,724

Consolidated_Statement_of_Comp

Consolidated Statement of Comprehensive Operations Statement (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
Statement of Comprehensive Income [Abstract]
NET INCOME (LOSS)	$14,892	$12,908	($10,335)
OTHER COMPREHENSIVE INCOME (LOSS):
Unrealized holding gains (losses) on available-for-sale securities	54	-3	5
Foreign currency translation adjustment	1	-49	-11
OTHER COMPREHENSIVE INCOME (LOSS), NET	55	-52	-6
TOTAL COMPREHENSIVE INCOME (LOSS)	$14,947	$12,856	($10,341)

Consolidated_Statements_of_Con

Consolidated Statements of Convertible Redeemable Preferred Stock and Stockholders' Equity (Deficit) (USD $)	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]	Redeemable Convertible Preferred Stock [Member]	Convertible Preferred Stock [Member]	Common Class B [Member]	Common Class B [Member]	Common Class B [Member]	Common Class A [Member]	Common Class A [Member]	Common Class A [Member]
In Thousands, except Share data, unless otherwise specified							Preferred Stock [Member]		Common Stock [Member]	Additional Paid-In Capital [Member]		Common Stock [Member]	Additional Paid-In Capital [Member]
Beginning balance at Jan. 01, 2012	($16,168)	$4	$2,229	$0	($18,401)		$0
Temporary equity, beginning balance at Jan. 01, 2012						45,519
Temporary Equity, beginning balance (in shares) at Jan. 01, 2012						54,862,065
Beginning balance, shares at Jan. 01, 2012		54,332,247					0
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of convertible redeemable preferred stock--net of issuance costs of $85 (in shares)						10,243,920
Issuance of convertible redeemable preferred stock—net of issuance costs of $85						84,916
Issuance of convertible redeemable preferred stock, issuance costs	85
Reclassification of temporary to permanent equity, shares						-38,536,593	38,536,593
Reclassifications of temporary to permanent equity	6,096		6,094			-6,096	2
Accretion of convertible redeemable preferred stock	-4,375		-3,303		-1,072	4,375
Increase (Decrease) in Stockholders' Equity [Roll Forward]
NET INCOME (LOSS)	-10,335				-10,335
Other comprehensive income (loss), net	-6			-6
Reclassifications of temporary to permanent equity	6,096		6,094			-6,096	2
Repurchase of convertible preferred stock (in shares)							-4,608,101
Repurchase of convertible preferred stock	-32,500		-6,557		-25,943
Accretion of convertible redeemable preferred stock	-4,375		-3,303		-1,072	4,375
Issuance of common stock (in shares)		229,493
Issuance of common stock	92	1	91
Stock based compensation	1,446		1,446
Ending balance at Dec. 30, 2012	-55,750	5	0	-6	-55,751		2
Temporary equity, ending balance at Dec. 30, 2012						128,714
Temporary Equity, ending balance (in shares) at Dec. 30, 2012						26,569,392
Ending balance, shares at Dec. 30, 2012		54,561,740					33,928,492
Increase (Decrease) in Temporary Equity [Roll Forward]
Reclassification of temporary to permanent equity, shares		60,621,233				-26,569,392
Reclassifications of temporary to permanent equity						-137,688
Accretion of convertible redeemable preferred stock	-8,974		-6,681		-2,293	8,974
Increase (Decrease) in Stockholders' Equity [Roll Forward]
NET INCOME (LOSS)	12,908				12,908
Other comprehensive income (loss), net	-52			-52
Reclassifications of temporary to permanent equity						-137,688
Accretion of convertible redeemable preferred stock	-8,974		-6,681		-2,293	8,974
Conversion of convertible preferred stock to common stock (in shares)							-33,928,492
Conversion of convertible preferred stock to common stock	137,688	6	137,684				-2
Issuance of common stock (in shares)									867,137			7,334,125
Issuance of common stock								1,039	0	1,039	147,543	1	147,542
Stock based compensation	7,801		7,801
Issuance of common stock, issuance costs	3,318
Ending balance at Dec. 29, 2013	242,203	12	287,385	-58	-45,136		0
Temporary equity, ending balance at Dec. 29, 2013						0
Temporary Equity, ending balance (in shares) at Dec. 29, 2013						0
Ending balance, shares at Dec. 29, 2013		123,384,235					0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
NET INCOME (LOSS)	14,892				14,892
Other comprehensive income (loss), net	55			55
Stock based compensation	14,564		14,564
Issuance of common stock upon exercise of stock options (in shares)	2,062,226	2,057,667
Issuance of common stock upon exercise of stock options	3,969	1	3,968
Vested restricted stock units converted to shares (in shares)		675
Excess tax benefit from stock-based compensation	280		280
Ending balance at Dec. 28, 2014	275,963	13	306,197	-3	-30,244		0
Temporary equity, ending balance at Dec. 28, 2014						$0
Temporary Equity, ending balance (in shares) at Dec. 28, 2014						0
Ending balance, shares at Dec. 28, 2014		125,442,577					0

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
CASH FLOWS FROM OPERATING ACTIVITIES:
NET INCOME (LOSS)	$14,892	$12,908	($10,335)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	13,449	6,240	3,369
Stock-based compensation	14,548	7,777	1,265
Excess tax benefit from stock-based compensation	-280	0	0
Deferred income taxes	843	0	0
Loss on disposal of assets	338	49	74
Changes in operating assets and liabilities:
Accounts receivable	-3,174	-2,131	-2,422
Inventories	-4,418	-5,399	-2,968
Prepaid expenses and other assets	-4,332	-1,827	-1,265
Accounts payable	54,235	20,820	14,150
Accrued expenses and other liabilities	22,901	21,092	8,329
Deferred revenue	21,012	13,591	6,086
Net cash provided by operating activities	130,014	73,120	16,283
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures	-67,757	-19,606	-7,858
Purchases of short-term and other investments	-191,448	-36,012	-10,200
Proceeds from maturity and sale of short-term and other investments	78,000	26,000	16,000
Purchases of restricted cash	0	-6,000	-9,281
Proceeds from maturity of restricted cash	0	6,682	11,200
Net cash used in investing activities	-181,205	-28,936	-139
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of convertible redeemable preferred stock	0	0	85,000
Convertible redeemable preferred stock issuance costs	0	0	-85
Proceeds from initial public offering, net of underwriter fees	0	150,863	0
Payments for deferred offering costs	-385	-2,933	0
Proceeds from issuance of common stock	0	1,029	78
Proceeds from exercise of stock options	3,966	0	0
Excess tax benefit from stock-based compensation	280	0	0
Repurchase and retirement of preferred stock	0	0	-32,500
Debt issuance costs	-408	-28	0
Net cash provided by financing activities	3,453	148,931	52,493
Effect of exchange rate changes on cash and cash equivalents	-59	-24	0
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	-47,797	193,091	68,637
CASH AND CASH EQUIVALENTS—Beginning of period	290,089	96,998	28,361
CASH AND CASH EQUIVALENTS—End of period	242,292	290,089	96,998
SUPPLEMENTAL DISCLOSURE OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Payable for capital purchases	288	84	205
Investment in common stock warrant	0	0	47
Stock-based compensation capitalized	16	24	181
Vesting of early exercised shares	6	10	13
Accretion of redeemable convertible preferred stock	0	8,974	4,375
Unpaid offering costs in additional paid-in capital	0	385	0
Deferred debt issuance costs	$0	$102	$0

Summary_of_Significant_Account

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 28, 2014
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
	Accounting Estimates—The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America (“GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Our significant estimates include assumptions related to the determination of deferred income taxes and any applicable related valuation allowances. Actual results could differ materially from those estimates.
	Foreign Currency Translation—The functional currency of the Company’s U.K. subsidiary is the British Pound Sterling. Assets and liabilities of the subsidiary are translated at the exchange rate in effect at each period-end. Income statement amounts are translated at the average rate of exchange prevailing during the period. Translation adjustments arising from the use of differing exchange rates from period to period are included in accumulated other comprehensive loss within stockholders’ equity (deficit).
	Cash and Cash Equivalents—Cash and cash equivalents include cash and highly-liquid investments with maturities of three months or less from the date of purchase, which are carried at amortized cost.
	Short-Term Investments—The Company classifies highly-liquid investments with maturities greater than three months but less than one year as short-term investments. Short-term investments are comprised of available-for-sale securities. Available-for-sale securities are recorded at fair value, and unrealized holding gains and losses are recorded as a component of accumulated other comprehensive loss in stockholders' equity (deficit), while realized gains and losses, and other-than-temporary impairments are reported as a component of net income. For the periods presented, realized and unrealized gains and losses on investments were not material. 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. The Company assesses 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, as well as the intent and ability to hold, or plans to sell, the investment. We did not identify any of our short-term investments as other-than-temporarily impaired for the fiscal years ended December 28, 2014 and December 29, 2013.
	Accounts Receivable—The majority of sales are conducted with credit cards and accounts receivable are composed primarily of amounts due from financial institutions related to those credit card sales. The Company does not maintain an allowance for doubtful accounts as payment is typically received within a few business days after the sale. Additionally, the Company includes other receivables, which consist of receivables for amounts owed as a result of tenant improvement allowances.
	Inventories—The Company’s inventories, which consist primarily of apparel, infant gear, toys and other merchandise are stated at the lower of cost or market and valued on an average cost basis. Inventory costs primarily consist of product costs from suppliers, as well as inbound shipping and handling fees. The majority of the Company’s inventories are not purchased until the Company receives a customer order and is subsequently relieved from inventories when it is delivered to the customer.
	Property and Equipment—Property and equipment are stated at cost, less accumulated depreciation. Maintenance and repairs are expensed as incurred. Depreciation is calculated on a straight-line basis over the estimated useful lives of the following asset categories:
	Asset Category	Depreciation Period
	Computer equipment and capitalized software	1 to 3 years
	Leasehold improvements	Lesser of 10 years or lease term
	Furniture, machinery and other equipment	3 to 15 years
	Capitalized Software—The Company capitalizes certain costs to develop its websites and internal-use software and amortizes such costs on a straight-line basis over the estimated useful life of the software once it is available for use. Capitalization of such costs begins when the preliminary project stage is completed, management with the relevant authority authorizes and commits to the funding of the software project, and it is probable that the project will be completed and the software will be used to perform the function intended.
	Capitalized software costs, net of accumulated amortization, totaled $3.6 million and $2.7 million as of December 28, 2014 and December 29, 2013, respectively, and are included in property and equipment—net in the accompanying consolidated balance sheets. Amortization expense related to capitalized software costs was $1.7 million, $1.0 million, and $0.6 million for the fiscal years ended December 28, 2014, December 29, 2013, and December 30, 2012, respectively, and is included in selling, general, and administrative expenses in the accompanying consolidated statements of operations.
	Impairment of Long-Lived Assets—The Company reviews the carrying value of its long-lived assets, including property and equipment and definite-lived intangible assets, whenever events or changes in circumstances indicate that the carrying value may not be recoverable. To the extent the estimated future cash inflows attributable to the assets, less estimated future cash outflows, are less than the carrying amount, an impairment loss would be recognized. No impairment losses were recorded in the periods presented.
	Fair Value of Financial Instruments—The carrying amounts for the Company’s cash, cash equivalents, short-term investments, accounts receivable, accounts payable and accrued liabilities approximate fair value due to their short maturities.
	Income Taxes—The Company uses the asset and liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are recognized by applying the statutory tax rates in effect in the years in which the differences between the financial reporting and tax filing bases of existing assets and liabilities are expected to reverse. Valuation allowances are established when necessary to reduce deferred tax assets to the amounts expected to be realized.
	The Company utilizes a two-step approach to recognizing and measuring uncertain income tax positions (tax contingencies). The first step is to evaluate the tax position for recognition by determining if the weight of available evidence indicates it is more likely than not that the position will be sustained on audit, including resolution of related appeals or litigation processes. The second step is to measure the tax benefit as the largest amount which is more than 50% likely of being realized upon ultimate settlement. The Company considers many factors when evaluating and estimating its tax positions and tax benefits, which may require periodic adjustments and which may not accurately forecast actual outcomes.
	The Company’s policy is to recognize interest and/or penalties related to all tax positions in income tax expense. To the extent that accrued interest and penalties do not ultimately become payable, amounts accrued will be reduced and reflected as a reduction of the overall income tax provision in the period that such determination is made. No interest and penalties were accrued as of December 28, 2014 and December 29, 2013.
	Certain Risks and Concentrations—The Company maintains the majority of its cash and cash equivalents in accounts with major financial institutions within the United States, generally in the form of demand and money market accounts. Deposits in these institutions may exceed federally insured limits. The Company has not experienced any losses on its deposits of cash and cash equivalents.
	The Company is subject to certain risks and concentrations, including dependence on third-party technology providers and hosting services, exposure to risks associated with online commerce security, consumer credit risk, and credit card fraud, as well as the interpretation of state and local laws and regulations in regards to the collection and remittance of sales and use taxes and occupancy taxes. The Company also depends upon third-party service providers for processing customer orders.
	Revenue Recognition—The Company generates net sales from sales of women's, children’s and men's apparel, children's merchandise and other product categories such as kitchen accessories and home décor, and from shipping and handling charges to the Company’s customers. The Company also generates net sales from the sale of services events, which are primarily electronic vouchers or access codes for the Company’s customers to redeem directly with the vendor. Net sales of services events have not been material to date.
	The Company recognizes revenue when the following criteria are met: (1) persuasive evidence of an arrangement exists; (2) delivery has occurred; (3) the selling price is fixed or determinable; and (4) collectability is reasonably assured. For product sales, these criteria are met when the customer orders an item through the Company’s sites via the electronic shopping cart, funds are collected from the customer and the item is fulfilled in one of the Company or third-party fulfillment centers, shipped and delivered to the customer. Revenue from product sales is generally recorded at the gross amount as the Company is the primary obligor in the arrangement with the customer, has latitude in establishing the products available for sale and the price to the customer, is responsible for ensuring the delivery of the product to the customer and assume inventory and credit risk. For services sales, these criteria are met when the customer orders an item through the Company’s sites via the electronic shopping cart, funds are collected from the customer and the voucher or access code is downloaded from the Company’s sites. Revenue from services sales is generally recorded at the net amount, or the commission earned on the voucher, as the Company is acting as an agent on behalf of the vendor. The vendor is ultimately responsible for fulfilling the customer order directly with the customer and assumes the inventory risk. To date, services revenue has not been material. The Company defers revenue when cash is collected from the customer prior to the satisfaction of the revenue recognition criteria.
	To encourage customers to purchase the Company’s products and services, the Company periodically provides incentive offers. Generally, these promotions include dollar-off and percentage-off discounts to be applied against current purchases. The Company also grants merchandise credits to participants in the Company’s referral program when the customer referral results in a sale. Merchandise credits issued through the referral program typically expire in 18 months. The Company records these discounts and merchandise credits as reductions of the sale price at the date the promotion is redeemed similar to a coupon. Additionally, the Company provides customers merchandise credits to be applied against future purchases in instances in which the customer is unsatisfied with an order. In these instances, the Company has established a sales return reserve based on the Company’s historical experience. To date, these reserves have not been significant.
	Gift cards and merchandise credits issued in lieu of a cash refund are recorded as a liability upon purchase of the gift card or issuance of the merchandise credit and do not expire. The Company reduces the liability for gift cards and merchandise credits when redeemed by a customer. If a gift card or merchandise credit is not redeemed, the Company recognizes revenue when the likelihood of its redemption becomes remote. The Company has not recognized revenue related to unredeemed gift cards and merchandise credits.
	The Company has procedures in place to detect and prevent credit card fraud as the Company has exposure to losses from fraudulent charges. Due to the insignificant losses related to chargebacks, the Company records such losses as incurred.
	Taxes collected from customers are accounted for on a net basis and are excluded from net sales.
	Cost of Sales—Cost of sales consists of the purchase price of merchandise sold to customers, inbound and outbound shipping and handling costs, shipping supplies and fulfillment costs. Fulfillment costs represent those costs incurred in operating and staffing the fulfillment centers, including costs attributed to receiving, inspecting, picking, packaging and preparing customer orders for shipment. Cost of sales also includes direct and indirect labor for fulfillment center oversight, including payroll and related benefit costs and stock-based compensation expense.
	Marketing—Marketing expenses are expensed as incurred and consist primarily of targeted online marketing costs, such as display advertising, keyword search campaigns, search engine optimization and social media and offline marketing costs such as television, radio and print advertising. Marketing expenses also include payroll and related benefit costs and stock-based compensation expense for employees involved in marketing activities. Marketing expenses are primarily related to growing and retaining the customer base.
	Selling, General and Administrative Expenses—Selling, general and administrative expenses (“SG&A”) consist primarily of payroll and related benefit costs and stock-based compensation expense for employees involved in general corporate functions including merchandising, studio, technology and customer service, as well as costs associated with the use by these functions of facilities and equipment, including depreciation, rent and occupancy. Also included in SG&A is rent and depreciation related to fulfillment centers.
	Stock-Based Compensation—The Company measures compensation cost for all stock options and restricted stock unit awards granted at their grant date estimated fair value. Stock-based compensation expense, net of estimated forfeitures, is recognized on a straight-line basis over the vesting period for each award. The fair value of stock option awards is estimated on the grant date using the Black-Scholes option valuation model. The fair value of each restricted stock unit award is based on the estimated fair market value of the Company’s common stock on the date of the award. See Note 8: "Stockholders' Equity (Deficit)" for additional details.
	Recent Accounting Guidance—
	Recently adopted accounting guidance
	In July 2013, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update No. 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar tax Loss, or a Tax Credit Carryforward Exists ("ASU 2013-11").The amendments in this update require an unrecognized tax benefit, or a portion of an unrecognized tax benefit, to be presented in the financial statements as a reduction to a deferred tax asset for a net operating loss carryforward, a similar tax loss, or a tax credit carryforward, except as follows: To the extent a net operating loss carryforward, a similar tax loss, or a tax credit carryforward is not available at the reporting date under the tax law of the applicable jurisdiction to settle any additional income taxes that would result from the disallowance of a tax position or the tax law of the applicable jurisdiction does not require the entity to use, and the entity does not intend to use the deferred tax asset for such purpose, the unrecognized tax benefit should be presented in the financial statements as a liability and should not be combined with deferred tax assets. The assessment of whether a deferred tax asset is available is based on the unrecognized tax benefit and deferred tax asset that exist at the reporting date and should be made presuming disallowance of the tax position at the reporting date. The amendments in this update do not require new recurring disclosures. For public entities, ASU 2013-11 is effective for annual and interim periods beginning after December 15, 2013. The Company adopted ASU 2013-11 in the first quarter of 2014 and it did not have a material impact on the Company's consolidated financial statements or related disclosures.
	Recent accounting guidance not yet adopted
	In May 2014, the FASB issued an Accounting Standard Update No. 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”) amending revenue recognition guidance and requiring 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. The guidance is effective for annual and interim reporting periods beginning after December 15, 2016, with early adoption prohibited. The Company is currently evaluating the impact ASU 2014-09 will have on its consolidated financial statements.
	In August 2014, the FASB issued ASU 2014-15 related to going concern. The new guidance explicitly requires that management assess an entity's ability to continue as a going concern and may require additional detailed disclosures. ASU 2014-15 is effective for annual periods beginning after December 15, 2016 and interim periods within those annual periods. Though permitted, the Company does not plan to early adopt. The Company does not believe that this standard will have a significant impact on its consolidated financial statements.

The_Company_and_Basis_of_Prese

The Company and Basis of Presentation	12 Months Ended
	Dec. 28, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
The Company and Basis of Presentation	THE COMPANY AND BASIS OF PRESENTATION
	The Company—zulily, inc. (the “Company”, "we", "us" or "our") is an online retailer offering customers a fun and entertaining shopping experience with a fresh selection of new product styles launched each day. Through the Company’s desktop and mobile sites and mobile applications, the Company helps its customers discover new and unique products at great values that they would likely not find elsewhere. The Company, a Delaware corporation formed in 2009, primarily conducts its buying, marketing and administrative functions in Seattle, Washington. The Company also operates a buying and studio office in Columbus, Ohio, a customer service office in Gahanna, Ohio and fulfillment centers in McCarran, Nevada and Lockbourne, Ohio.
	Principles of Consolidation—The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany transactions and balances are eliminated in consolidation.
	Reclassifications—Certain reclassifications have been made to the condensed consolidated financial statements in the prior period to conform to the current period presentation. Specifically, merchandise deposits are included in prepaid expenses and other current assets as of December 28, 2014 and December 29, 2013. As of December 29, 2013, we reclassified $0.5 million related to merchandise deposits to prepaid expenses and other current assets.
	Fiscal Year—The Company utilizes a retail calendar whereby the fiscal year ends on the Sunday closest to December 31. Each fiscal year consists of four 13-week quarters, with one extra week added in the fourth quarter every five to six years.

Accrued_Expenses

Accrued Expenses	12 Months Ended
	Dec. 28, 2014
Payables and Accruals [Abstract]
Accrued Expenses	ACCRUED EXPENSES
	Accrued expenses consist of the following:
		December 28,		December 29,
		2014		2013
		(in thousands)
	Accrued payroll	$	12,607	$	5,327
	Accrued marketing	6,655		3,595
	Accrued shipping	10,063		15,186
	Other accrued expenses	10,149		6,665
	Total accrued expenses	$	39,474	$	30,773

Property_and_Equipment

Property and Equipment	12 Months Ended
	Dec. 28, 2014
Property, Plant and Equipment [Abstract]
Property and Equipment	PROPERTY AND EQUIPMENT
	The balance of property and equipment—net is as follows:
		December 28,			December 29,
		2014			2013
		(in thousands)
	Computer equipment and capitalized software	$	24,111		$	15,963
	Leasehold improvements	26,166			1,272
	Furniture, machinery and other equipment	49,824			12,224
	Work in progress	1,261			5,228
	Less: accumulated depreciation and amortization	(22,464		)	(10,074		)
	Total property and equipment, net	$	78,898		$	24,613
	Depreciation and amortization expense of property and equipment totaled $13.1 million, $6.2 million, and $3.4 million during the fiscal years ended December 28, 2014, December 29, 2013, and December 30 2012, respectively.

Commitment_and_Contingencies

Commitment and Contingencies	12 Months Ended
	Dec. 28, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES
	Leases—The Company leases office and warehouse space and equipment used in connection with its operations under various operating leases, some of which provide for rental payments on a graduated basis, rent holidays and other incentives. At the inception of the lease, the Company evaluates each agreement to determine whether the lease will be accounted for as an operating or capital lease. The Company records rent expense on a straight-line basis over the lease period. Any lease incentives are recognized as reductions of rental expense on a straight-line basis over the term of the lease.
	Rental expense was $8.3 million, $5.9 million and $4.6 million for the fiscal years ended December 28, 2014, December 29, 2013 and December 30, 2012, respectively.
	Future minimum payments under noncancelable operating leases as of December 28, 2014 are as follows:
	Fiscal Years Ending	Amount
		(in thousands)
	2015	$	15,370
	2016	16,464
	2017	15,492
	2018	14,962
	2019	15,392
	Thereafter	66,503
	Total	$	144,183
	Sales Taxes—To date, the Company has had no actual or threatened sales and use tax claims from any state where zulily does not already claim nexus. However, the Company believes that the likelihood of incurring a liability as a result of sales tax nexus being asserted by certain states where it doesn’t currently collect sales tax is reasonably possible. As of December 28, 2014, the Company is unable to estimate the possible loss or range of loss as it is an unasserted possible liability that would be contested and subject to negotiation between the taxpayer and the state or decided by a court.
	Legal Proceedings—In the ordinary course of business, the Company may be involved in various legal proceedings, lawsuits, disputes or claims related to, among other things, alleged infringement of third-party patents and other intellectual property rights, commercial and consumer matters, product compliance and employment matters. We have been, and may in the future be, put on notice and/or sued by third parties for alleged infringement of their proprietary rights, including patent, trademark and copyright infringement, as well as employment claims. The outcome of any such claim or litigation is inherently uncertain. Any claims against us, whether meritorious or not, could be time-consuming, result in costly litigation, damage our reputation, require significant amounts of management time and divert significant resources. Although the Company cannot predict the outcome of any such claims or litigation, it does not believe there are currently any such claims or litigation that, if resolved unfavorably, would have a material impact on the Company's financial condition, results of operations or cash flows.

Credit_Facility

Credit Facility	12 Months Ended
	Dec. 28, 2014
Debt Disclosure [Abstract]
Credit Facility	CREDIT FACILITY
	In January 2014, the Company entered into a $50.0 million revolving credit facility pursuant to a Credit Agreement with certain lenders (the "Credit Agreement"). Any borrowings under the Credit Agreement mature in January 2016. Borrowings under the Credit Agreement bear annual interest, at the Company's option, in an amount equal to (i) in the case of base rate loans, 1.50% plus the highest of (a) the Federal Funds Rate plus one-half of one percent (0.50%), (b) the prime rate, and (c) the eurodollar rate plus two percent (2.00%), or (ii) in the case of eurodollar loans, for any interest period, LIBOR plus 2.50%. An undrawn commitment fee shall be payable to the lenders in an amount equal to 0.175% times the actual daily amount by which the aggregate commitments exceed the sum of the outstanding amount of loans and the outstanding amount of letter of credit obligations, calculated on a quarterly basis in arrears. The Credit Agreement contains certain customary representations and warranties, financial covenants, events of default and is secured by substantially all of the assets of the Company. As of the filing date of this Annual Report, no amounts have been drawn down under the revolving credit facility.

Retirement_Plan

Retirement Plan	12 Months Ended
	Dec. 28, 2014
Compensation and Retirement Disclosure [Abstract]
Retirement Plan	RETIREMENT PLAN
	The Company offers a salary deferral 401(k) plan for its U.S. employees. The plan allows employees to contribute a percentage of their pretax earnings annually, subject to limitations imposed by the Internal Revenue Service. The plan also allows us to make a matching contribution, subject to certain limitations. The Company has incurred costs relating to the matching contribution of $0.6 million for the fiscal year ended December 28, 2014, which was paid out in early 2015. For the fiscal years ended December 29, 2013 and December 30, 2012 we incurred no costs and made no contributions to the plan.

Stockholders_Equity_Deficit

Stockholders' Equity (Deficit)	12 Months Ended
	Dec. 28, 2014
Equity [Abstract]
Stockholders' Equity (Deficit)	STOCKHOLDERS’ EQUITY (DEFICIT)
	Initial Public Offering
	In November 2013, the Company completed its IPO in which it issued and sold 7,334,125 shares of Class A common stock at a public offering price of $22.00 per share and the selling stockholders sold 5,890,875 shares of Class A common stock. The Company did not receive any proceeds from the sale of shares by the selling stockholders. The total net proceeds from the offering to the Company were $147.5 million after deducting the underwriting discounts and offering expenses totaling $3.3 million.
	Preferred Stock
	The Company has 2,000,000 shares of undesignated preferred stock authorized for future issuance. Shares of preferred stock may be issued from time to time in one or more series with rights, preferences and privileges established by the Company's board of directors.
	Common Stock
	Since October 17, 2013, the Company has had two classes of authorized common stock outstanding: Class A common stock and Class B common stock, with 500,000,000 and 275,000,000 shares authorized, respectively. As of December 28, 2014, the Company had outstanding 61,327,351 shares of Class A common stock and 64,115,226 shares of Class B common stock. The rights of the holders of Class A common stock and Class B common stock are identical, except with respect to voting and conversion. The holders of Class A common stock are entitled to one vote per share, and the holders of Class B common stock are entitled to ten votes per share, on all matters that are subject to stockholder vote. Each share of Class B common stock may be converted into one share of Class A common stock at the option of its holder and will be automatically converted into one share of Class A common stock upon transfer, with certain limited exceptions.
	Restricted Common Stock
	On October 26, 2009, the Company signed a Restricted Stock Purchase Agreement with its founders wherein each founder purchased shares of Class B common stock at a price of $0.0004 per share and granted the Company an option to acquire shares of Class B common stock owned by the respective founders at a repurchase right equal to the lesser of the original price paid for each share or the fair market value on the date of repurchase of said shares. Common stock under the Restricted Stock Purchase Agreement provided for monthly vesting over four years, some of which provide for 25% vesting on the first anniversary from the date of issuance or hire date with the remainder vesting monthly over the subsequent three years. The repurchase right was exercisable on unvested shares during the 90-day period following the date a founder ceases for any reason to provide service to the Company. As of December 28, 2014 all 52,812,500 Class B common shares under restricted stock purchase agreements entered into with the Company's founders have fully vested. As of December 29, 2013, 52,792,969 shares had vested and 19,531 were expected to vest. No amount of compensation expense has been recognized in connection with these shares, as they were deemed to have nominal value at the date of issuance.
	Equity Incentive Plans
	The Company has two equity incentive plans: the 2009 Equity Incentive Plan (the "2009 Plan") and the 2013 Equity Plan (the "2013 Plan"). Under the 2009 Plan, 18,105,313 shares of Class B common stock were reserved for issuance of incentive stock options ("ISOs"), nonstatutory stock options ("NSOs"), stock appreciation rights, restricted stock awards, restricted stock unit awards ("RSUs") and other stock-based payment awards to employees, directors and consultants. Upon the IPO, 11,795,185 shares of Class A common stock were initially reserved under the 2013 Plan and 1,627,200 shares of Class B common stock that were reserved under the 2009 Plan but not issued were assumed by the 2013 Plan for future issuance as Class A common stock awards. The 2013 Plan will also assume the maximum number of shares subject to stock options or other awards granted under the 2009 Plan that may be returned to the 2009 Plan, such as upon expiration or termination of a stock award prior to vesting. The maximum number of shares of Class A common stock issuable under the 2013 Plan is 27,610,562. However, the 2013 Plan provides that such maximum number of shares shall increase pursuant to an "evergreen" provision contained therein. Pursuant to such provision, beginning December 30, 2013, the number of shares reserved for issuance under the 2013 Plan will automatically increase on the first day of each fiscal year through the first day of fiscal year 2023 by the lesser of (a) four percent (4%) of the total number of shares of the Company's capital stock outstanding on the last day of the preceding fiscal year and (b) a number determined by the Company's board of directors. As of December 28, 2014, there were 18,122,045 shares available for issuance under the 2013 Plan. No new awards will be issued under the 2009 Plan. Under the 2013 Plan, the Company has the ability to issues ISOs, NSOs, stock appreciation rights, restricted stock awards, RSUs and other stock awards. The ISOs and NSOs will be granted at a price per share not less than the fair value at the date of grant. Options granted to date generally provide for 25% vesting on the first anniversary from the date of grant with the remainder vesting monthly over the subsequent three years and expire 10 years from the date of grant. RSUs granted to date generally provide for graded vesting over five years and expire 10 years from the date of grant.
	Stock-Based Compensation Expense
	The fair value of options granted to employees is estimated on the grant date using the Black-Scholes option pricing model. The assumptions used to calculate the fair value of options granted are evaluated and revised, as necessary, to reflect market conditions and the Company’s experience. The Black-Scholes option pricing model requires inputs such as expected term, expected volatility and risk-free interest rate. These inputs are subjective and generally require significant analysis and judgment to develop. Due to the limited period of time the Company’s equity shares have been publicly traded, the Company uses the simplified method provided by the SEC in estimating the expected term. This represents the average period from vesting to the expiration of the stock option. During the fiscal year ended December 28, 2014, the Company began incorporating its own expected volatility based on daily price observations for the full period in which its shares publicly traded as a data point in addition to the peer companies previously used to calculate volatility. The dividend yield is 0%, since the Company has not paid, and does not expect to pay, dividends. The risk-free interest rate is based on the implied yield available on U.S. Treasury issues with an equivalent remaining term.
	The fair value of each stock option is estimated on the grant date with the following weighted-average assumptions:
		Year Ended
		December 28,				December 29,				December 30,
		2014				2013				2012
	Expected term (years)	6.1				6.66				5.98
	Expected volatility	54.7		%		50.9		%		61.7		%
	Expected dividend yield	—		%		—		%		—		%
	Risk-free interest rate	1.9		%		1.3		%		1		%
	Weighted average grant-date fair value of stock options granted	$	21.41			$	6.75			$	4.1
	The fair value of RSU awards to our employees, officers and non-employee directors is determined by using the closing price of our Class A common stock as reported on the NASDAQ Global Select Market on the date of grant. An RSU award entitles the holder to receive shares of the Company’s Class A common stock as the award vests, which is generally based on length of service. The Company's non-vested RSUs do not have nonforfeitable rights to dividends or dividend equivalents.
	The following table presents the effects of stock-based compensation on the consolidated statements of operations during the periods presented:
		Year Ended
		December 28,				December 29,				December 30,
		2014				2013				2012
		(in thousands)
	Cost of sales	$	210			$	70			$	26
	Marketing expenses	790				327				142
	Selling, general and administrative expenses	13,548				7,380				1,097
	Total stock-based compensation expense	$	14,548			$	7,777			$	1,265
	The Company recognizes compensation expense on a straight-line basis over the requisite service period for each stock option and RSU, with forfeitures estimated at the date of grant based on the Company’s historical experience and future expectations.
	As of December 28, 2014, the Company had total unrecognized compensation costs related to stock options of $49.7 million. The Company expects to recognize this cost over a weighted-average period of 4.85 years.
	The following table summarizes additional information about stock options outstanding as of December 28, 2014:
		Outstanding									Outstanding and Vested
					Weighted Average
	Range of Exercise Price	Options			Exercise				Remaining		Options		Weighted
					Price				Contractual				Average
									Life				Exercise Price
									(in Years)
	$0.028 - $0.312	1,735,762			$	0.26			5.91		1,716,878		$	0.26
	$0.717 - $7.44	1,043,938			$	4.47			6.86		848,034		$	4.11
	$7.48 - $10.28	7,778,683			$	9.6			8.24		6,371,090		$	9.89
	$13.44 - $41.43	1,153,776			$	20.95			8.86		308,922		$	18.36
	$41.79 - $53.89	366,788			$	43.79			9.16		—		$	—
	Total	12,078,947									9,244,924
	The table summarizes stock option activity as follows:
		Number of			Weighted				Weighted		Total
		Shares			Average				Average		Intrinsic
		Underlying			Exercise				Remaining		Value
		Options			Price				Contractual
									Term
									(in Years)
		(in thousands, except price, shares and years)
	Outstanding at December 29, 2013	13,938,487			$	7.4			8.56		$	462,558
	Granted	681,840			40.87
	Exercised	(2,062,226	)		1.92
	Canceled	(479,154	)		14.88
	Outstanding at December 28, 2014	12,078,947			9.93				7.87		172,655
	Vested and expected to vest at December 28, 2014	11,873,058			9.77				7.85		170,874
	Exercisable at December 28, 2014	9,244,924			7.85				7.72		142,630
	During the fiscal year ended January 1, 2012, the Company issued 1,439,627 Class B common shares for the exercise of stock options. Of this amount, 473,958 Class B common shares were early exercised and are subject to repurchase in accordance with the provision of the 2009 Plan. The unvested portion of the early exercised shares as of December 28, 2014 and December 29, 2013, was zero and 63,151 shares, respectively.
	Exercisable stock options as of December 28, 2014 and December 29, 2013 include 4,761,744 and 5,462,661 options that are early exercisable, respectively.
The table summarizes RSU awards activity as follows:
	Number of Shares Underlying RSUs			Weighted Average Grant-Date Fair Value per RSU
Outstanding at December 29, 2013	—			$	—
Granted	379,888			35.49
Vested	(675	)		34.36
Forfeited	(14,083	)		36.23
Outstanding at December 28, 2014	365,130			$	35.47
As of December 28, 2014, the Company had total unrecognized compensation costs related to RSU awards of $10.3 million. The Company expects to recognize this cost over a weighted-average period of 4.66 years.

Net_Income_Loss_Per_Share

Net Income (Loss) Per Share	12 Months Ended
	Dec. 28, 2014
Earnings Per Share [Abstract]
Net Income (Loss) Per Share	NET INCOME (LOSS) PER SHARE
	Net income (loss) per common share is presented using the two-class method required for participating securities. Concurrent with the closing of the IPO in November 2013, all shares of outstanding preferred stock automatically converted into 60,621,233 shares of the Company's Class B common stock. Prior to the IPO, the Company considered all holders of preferred stock to be participating securities as they were entitled to receive non-cumulative dividends. Additionally, the Company considers holders of unvested restricted common stock to be participating securities because of their non-forfeitable rights to dividends, in the event dividends are declared and paid. During the fiscal year ended December 28, 2014, the Company did not consider the unvested restricted common stock to be participating securities because there would be no change to the reported net income (loss) per share.
	Following the completion of the Company's IPO in November 2013, Class A and Class B common stock are the only outstanding equity in the Company. The rights of the holders of Class A and Class B common stock are identical, except with respect to voting and conversion. Each share of Class A common stock is entitled to one vote per share and each share of Class B common stock is entitled to ten votes per share, on all matters that are subject to stockholder vote. Shares of Class B common stock may be converted into Class A common stock at any time at the option of the stockholder, and are automatically converted upon transfer to Class A common stock, subject to certain limited exceptions.
	Undistributed earnings allocated to the participating securities are subtracted from net income in determining net income attributable to Class A and Class B common stockholders. Net losses are not allocated to the participating securities as holders of preferred stock and unvested restricted common stock do not have a contractual obligation to share in the losses of the Company. Undistributed earnings are calculated as net income (loss) less distributed earnings, accretion of convertible preferred stock, and current period convertible preferred stock non-cumulative dividends, whether or not declared. Basic net income (loss) per share is computed by dividing net income attributable to Class A and Class B common stockholders by the weighted-average number of shares of Class A and Class B common stock outstanding during the period.
	For the calculation of diluted net income (loss), net income attributable to Class A and Class B common stockholders for basic net income is adjusted by the effect of dilutive securities, including awards under our equity compensation plans. Diluted net income (loss) per share attributable to Class A and Class B common stockholders is computed by dividing the resulting net income attributable to Class A and Class B common stockholders by the weighted-average number of fully diluted Class A and Class B common shares outstanding.
	For the fiscal years ended December 28, 2014 and December 29, 2013, the computation of basic and diluted net income (loss) per share is presented on a combined basis for Class A and Class B common stock because the results are identical.
	The following table presents the calculation of basic and diluted net income (loss) per common share:
		Year Ended
		December 28,			December 29,			December 30,
		2014			2013			2012
		(in thousands, except share and per share amounts)
	Numerator
	Net income (loss)	$	14,892		$	12,908		$	(10,335	)
	Less: Accretion of convertible redeemable preferred stock	—			(8,975		)	(4,375		)
	Less: Distributed earnings attributable to participating securities	—			—			(32,112		)
	Less: Undistributed earnings attributable to participating securities	—			(3,933		)	—
	Net income (loss) attributable to Class A and Class B common stockholders	$	14,892		$	—		$	(46,822	)
	Denominator
	Weighted average shares used to compute basic net income (loss) per Class A and Class B common share	124,679,716			59,450,186			37,976,724
	Effect of potentially dilutive securities:
	Stock options	7,615,037			—			—
	Restricted stock unit awards	22,604			—			—
	Weighted average shares used to compute diluted net income (loss) per Class A and Class B common share	132,317,357			59,450,186			37,976,724
	Net income (loss) per share attributable to Class A and Class B common stockholders—basic	$	0.12		$	—		$	(1.23	)
	Net income (loss) per share attributable to Class A and Class B common stockholders—diluted	$	0.11		$	—		$	(1.23	)
	The following have been excluded from the computation of basic and diluted net income (loss) per share attributable to Class A and Class B common stockholders as their effect would have been antidilutive:
		Year Ended
		December 28,		December 29,			December 30,
		2014		2013			2012
	Convertible preferred shares	—		53,184,953			55,827,571
	Unvested restricted common shares	—		3,644,546			16,468,775
	Stock options	403,742		13,938,487			7,430,501
	Restricted stock unit awards	137,110		—			—
	Total	540,852		70,767,986			79,726,847

Segment_Information

Segment Information	12 Months Ended
	Dec. 28, 2014
Segment Reporting [Abstract]
Segment Information	SEGMENT INFORMATION
	The Company has two reportable segments: North America and United Kingdom ("U.K."). The Company’s reportable segments have been identified based on how the Company’s chief operating decision maker manages the Company’s businesses, makes operating decisions, and evaluates operating performance. The Company’s chief operating decision maker is its chief executive officer. The Company evaluates the performance of its reportable segments based on net sales and operating income (loss). The accounting policies of the reportable segments are the same as those described in the summary of significant accounting policies in Note 2, "Summary of Significant Accounting Policies". Operating income (loss) represents net loss before interest income (expense), net, other income (expense), net and provision for income taxes. Management does not evaluate the performance of its reportable segments using asset measures.
	North America—The North America segment consists of amounts earned from retail and services sales through the Company’s U.S.-operated sites, including sales from the sites to customers in the United States, Canada, Australia and other foreign countries.
	U.K.—The U.K. segment consists of amounts earned from retail and services sales through the Company’s U.K.-operated sites, including sales from the sites to customers in the United Kingdom and other countries in Europe.
	Certain corporate-level activities are not allocated to the U.K. segment, including costs of marketing, human resources, legal, finance and technology.
	The Company accounts for intersegment sales in accordance with the underlying transfer pricing agreement between zulily, inc. and Zulily UK Ltd.
	Information on reportable segments and reconciliation to consolidated net income (loss) before provision for income taxes is as follows:
		Year Ended
		December 28,			December 29,			December 30,
		2014			2013			2012
		(in thousands)
	North America
	Net sales	$	1,181,501		$	681,826		$	326,349
	Operating income (loss)	20,715			17,173			(6,072		)
	Intersegment expense	(4,951		)	(4,093		)	(4,571		)
	Total segment operating income (loss)	15,764			13,080			(10,643		)
	U.K.
	Net sales	18,578			13,883			4,891
	Intersegment sales	4,951			4,093			4,571
	Total net sales	23,529			17,976			9,462
	Segment operating income (loss)	$	(34	)	$	(51	)	$	89
	Consolidated
	Net sales
	Total sales for reportable segments	$	1,205,030		$	699,802		$	335,811
	Elimination of intersegment sales	(4,951		)	(4,093		)	(4,571		)
	Total consolidated net sales	$	1,200,079		$	695,709		$	331,240
	Net income (loss) before provision for income taxes
	Total operating income (loss) for reportable segments	$	15,730		$	13,029		$	(10,554	)
	Interest income (expense)—net	317			136			43
	Other income (expense)—net	(46		)	99			176
	Net income (loss) before provision for income taxes	$	16,001		$	13,264		$	(10,335	)
	The Company’s assets are primarily located in the United States as of the fiscal years ended December 28, 2014, December 29, 2013 and December 30, 2012. Net sales from external customers for each group of similar products and services are not reported to the Company’s chief operating decision maker. The separate identification of this information for purposes of segment disclosure is impracticable, as it is not readily available and the cost to develop it would be excessive.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 28, 2014
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES
	The components of income (loss) before provision for income taxes are as follows:
		Year Ended
		December 28,				December 29,				December 30,
		2014				2013				2012
		(in thousands)
	U.S.	$	16,001			$	13,266			$	(10,401	)
	Foreign	—				(2		)		66
	Income before income taxes	$	16,001			$	13,264			$	(10,335	)
	For the fiscal years ended December 28, 2014, December 29, 2013, and December 30, 2012 the Company recorded tax provisions of $1.1 million, $0.4 million and zero, respectively. The Company currently has tax benefits relating to prior year net operating losses that are being utilized to reduce the Company's U.S. taxable income.
	Income taxes have been provided as follows:
		Year Ended
		December 28,				December 29,				December 30,
		2014				2013				2012
		(in thousands)
	Current tax expense:
	Federal	$	546			$	356			$	—
	State and Local	—				—				—
	Foreign	—				—				—
	Current tax expense	546				356				—
	Deferred tax expense:
	Federal	537				—				—
	State and Local	26				—				—
	Foreign	—				—				—
	Deferred tax expense	563				—				—
	Provision for income taxes	$	1,109			$	356			$	—
	Reconciliation of income tax computed at federal statutory rates to the reported provisions for income taxes is as follows:
		Year ended
		December 28,			December 29,			December 30,
		2014			2013			2012
	Federal statutory rate	35	%		35	%		(34.0	)%
	Effect of:
	State and local income tax	—			—			(1.0	)
	Non-deductible expenses	0.3			0.2			(0.1	)
	R&D tax credit generated in current year	(5.4	)		(2.3	)		(4.6	)
	Stock-based compensation	2			5.6			4.2
	Other	0.2			0.1			0.4
	Valuation allowance	(25.1	)		(35.9	)		35.1
	Total	7	%		2.7	%		—	%
	The Company's effective tax rate for the fiscal years ended December 28, 2014 and December 29, 2013, was lower than the 35% U.S. federal statutory rate primarily due to the release of the Company's valuation allowance and the research and development credit benefit.
	Deferred tax assets and liabilities are summarized as follows:
		As Of
		December 28,				December 29,
		2014				2013
		(in thousands)
	Deferred tax assets:
	Tax loss carryforwards	$	18			$	2,402
	Returns and accruals	2,053				1,305
	Deferred rent	7,263				817
	Inventories	787				746
	Stock-based compensation	6,316				2,027
	Tax-credit carryforwards	1,376				1,236
	Other	52				—
	Deferred tax assets	17,865				8,533
	Deferred tax liabilities:
	Property and equipment	(18,041		)		(4,115		)
	Prepaid expenses and other current assets	(356		)		(400		)
	Unrealized foreign exchange gain	—				(34		)
	Deferred tax liabilities	(18,397		)		(4,549		)
	Valuation allowance	(31		)		(3,984		)
	Deferred tax asset (liability), net	$	(563	)		$	—
	Current asset (liability), net	$	17,827			$	2,675
	Noncurrent asset (liability), net	(18,390		)		(2,675		)
	Deferred tax asset (liability), net	$	(563	)		$	—
During the fiscal year ended December 28, 2014, the Company determined that it was more likely than not the Company’s deferred tax assets will be realized and released its valuation allowance related to U.S. deferred income taxes. In order to release the valuation allowance, the Company considered all available evidence, both positive and negative, including:
•	the nature, frequency, and severity of cumulative financial reporting losses in recent years;
•	the projected sustainability of recent operating profitability;
•	the predictability of future operating profitability of the character necessary to realize the net deferred tax asset; and
•	the carryforward periods for the net operating loss, capital loss and research and development tax credit carryforwards, including the effect of reversing taxable temporary differences.
The Company has emerged from cumulative losses during the fiscal year ended December 28, 2014 and has projections of sufficient future taxable income. These two items represent significant positive evidence and as of December 28, 2014, the cumulative positive evidence outweighed the historical negative evidence regarding the likelihood that the deferred tax asset for the Company's U.S. operations will be realized. This assessment was evidenced by the Company meeting all of the above criteria, resulting in its conclusion that $3.9 million of the deferred tax asset valuation allowance for the Company's U.S. operations should be released. However, a valuation allowance was maintained on the UK's net operating loss carryforwards.
The amount of the deferred tax assets considered realizable, however, could be reduced in the near term if the Company’s projections of future taxable income are reduced or if the Company does not perform at the levels it is projecting. This could result in increases to the valuation allowance for deferred tax assets and a corresponding increase to income tax expense of up to the entire net amount of deferred tax assets.
At December 28, 2014, the Company had federal and non-U.S. net operating loss carryforwards of $33.9 million and $0.5 million, respectively. The federal net operating loss carryforwards primarily relate to tax deductible stock-based compensation in excess of amounts recognized for financial statement purposes. To the extent that net operating loss carryforwards, if realized, relate to stock-based compensation, the resulting tax benefits will be recorded to shareholders' equity, rather than to results of operations. The Company also had $2.4 million of federal research and development tax credit carryforwards as of December 28, 2014 and $0.4 million of alternative tax credits. These carryforwards may be subject to limitations under the Internal Revenue Code and applicable state tax or local law. If not utilized, a portion of the carryforwards will begin to expire in 2031.
During the fiscal year ended December 28, 2014, the Company recognized excess tax benefits on stock option exercises of approximately $0.3 million, which were recorded to additional paid in capital.
Under Section 382 of the Internal Revenue Code, as amended (the “Code”), the Company’s ability to utilize net operating loss carryforwards or other tax attributes, such as research tax credits, in any taxable year may be limited if it experiences an “ownership change.” A Section 382 “ownership change” generally occurs if one or more stockholders or groups of stockholders who own at least 5% of the Company’s stock increase their ownership by more than 50 percentage points over their lowest ownership percentage within a rolling three-year period or since the date of a prior ownership change, if within three years. Similar rules may apply under state tax laws.
In this regard, the Company has determined that such an ownership change occurred and that based on the timing of the ownership change and the corresponding Section 382 limitation, none of its net operating losses or other tax attributes appear to expire subject to such limitation.
A reconciliation of the change in amount of gross unrecognized income tax benefits for the prior three years is as follows:
	Year Ended
	December 28,				December 29,				December 30,
	2014				2013				2012
	(in thousands)
Balance at the beginning of the year	$	377			$	—			$	—
Increase related to prior period tax positions	(40		)		172				—
Increase related to current period tax positions	369				205				—
Balance at the end of the year	$	706			$	377			$	—
As of December 28, 2014, the Company had $0.7 million in tax contingencies, of which the entire amount, if fully recognized, would decrease the Company's effective tax rate.
The Company is subject to taxation in the United States and various other state and foreign jurisdictions. The Company does not have any significant interest or penalty accruals. The statute of limitations for adjustments to our historic tax obligations will vary from jurisdiction to jurisdiction. Furthermore, net operating loss and tax credit carryforwards may be subject to adjustment after the expiration of the statute of limitations of the year such net operating losses and tax credits originated. In general, the tax years for U.S. federal and state income tax purposes, that remain open for examination are for 2009 and forward due to operating loss carryforwards.
Tax benefits for uncertain tax positions are based upon management's evaluation of the information available at the reporting date. To be recognized in the financial statements, a tax benefit must be at least more likely than not of being sustained based on technical merits. The benefit for positions meeting the recognition threshold is measured as the largest benefit more likely than not of being realized upon settlement with a taxing authority that has full knowledge of all relevant information. The Company has established a reserve for uncertain tax positions in regards to a portion of its federal research and development credits carryforwards.
To the extent that the research and development tax credits, if realized, relate to stock-based compensation, the resulting tax benefits will be recorded to the results of operations rather than stockholders' equity.

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 28, 2014
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS
	Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. To increase the comparability of fair value measures, the following hierarchy prioritizes the inputs to valuation methodologies used to measure fair value:
	Level 1—Quoted prices for identical assets and liabilities in active markets. The Company classifies cash equivalents as Level 1 in the fair value hierarchy. Cash equivalents are comprised of highly-liquid investments, including money market funds with original maturities of less than six months. The fair value measurement of these assets is based on quoted market prices in active markets and, therefore, these assets are recorded at fair value on a recurring basis.
	Level 2—Assets and liabilities valued based on observable market data for similar instruments, such as quoted prices for similar assets or liabilities or other inputs that are observable or can be corroborated by observable market data. The Company classifies restricted cash and short-term investments as Level 2 in the fair value hierarchy. Restricted cash is comprised of certificates of deposit funds with original maturities of less than three months. Short-term investments consist of commercial paper. The fair value measurement of these assets is based on observable market-based inputs or inputs that are derived principally from or corroborated by observable market data by correlation or other means.
	Level 3—Unobservable inputs reflecting the Company’s assumptions, consistent with reasonably available assumptions made by other market participants. These valuations require significant judgment. The Company does not have assets classified as Level 3 in the fair value hierarchy.
	The following tables summarize the Company's assets that are measured at fair value on a recurring basis, by level, within the fair value hierarchy as of December 28, 2014 and December 29, 2013:
		28-Dec-14
		Total		Level 1		Level 2		Level 3
		(in thousands)
	Cash equivalents:
	Money market funds	$	3,015	$	3,015	$	—	$	—
	Short-term investments:
	Commercial paper	131,528		—		131,528		—
	Total	$	134,543	$	3,015	$	131,528	$	—
		December 29, 2013
		Total		Level 1		Level 2		Level 3
		(in thousands)
	Cash equivalents:
	Money market funds	$	18,019	$	18,019	$	—	$	—
	Short-term investments:
	Commercial paper	18,014		—		18,014		—
	Total	$	36,033	$	18,019	$	18,014	$	—

Quarterly_Financial_Informatio

Quarterly Financial Information (Unaudited)	12 Months Ended
	Dec. 28, 2014
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information (Unaudited)	QUARTERLY FINANCIAL INFORMATION (UNAUDITED)
	The following tables contain selected unaudited statement of operations information for each quarter of 2014 and 2013. The following information reflects all normal recurring adjustments necessary for a fair presentation of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period. Our business is affected by seasonality, which historically has resulted in higher sales volume during our fourth quarter. Unaudited quarterly results are as follows:
		Quarters Ended
		Dec. 28, 2014		Sept. 28, 2014*			Jun. 29, 2014		Mar. 30, 2014
		(in thousands, except per share amounts)
	Net sales	$	391,349	$	285,836		$	285,013	$	237,881
	Gross profit	101,067		78,689			80,956		63,734
	Income (loss) from operations	11,669		(663		)	7,675		(2,951		)
	Net income (loss) before provision for income taxes	11,690		(495		)	7,756		(2,950		)
	Provision for income taxes	809		300			—		—
	Net income (loss)	$	10,881	$	(795	)	$	7,756	$	(2,950	)
	Net income (loss) attributable to Class A and Class B common stockholders	$	10,881	$	(795	)	$	7,756	$	(2,950	)
	Basic earnings per share	$	0.09	$	(0.01	)	$	0.06	$	(0.02	)
	Diluted earnings per share	$	0.08	$	(0.01	)	$	0.06	$	(0.02	)
	Shares used in computation of earnings per share:
	Basic	125,525		124,985			124,424		123,879
	Diluted	131,036		124,985			133,067		123,879
	*Includes the previously disclosed out-of-period correction of $2.8 million. The net impact of the adjustment was an increase to net sales of $2.8 million and a decrease to deferred revenue of the same amount.
		Quarters Ended
		Dec. 29, 2013		Sept. 29, 2013			Jun. 30, 2013		Mar. 31, 2013
		(in thousands, except per share amounts)
	Net sales	$	257,033	$	166,655		$	145,009	$	127,012
	Gross profit	68,375		44,501			43,903		36,612
	Income (loss) from operations	12,922		(2,283		)	4,003		(1,613		)
	Net income (loss) before provision for income taxes	13,109		(2,251		)	4,001		(1,595		)
	Provision for income taxes	356		—			—		—
	Net income (loss)	$	12,753	$	(2,251	)	$	4,001	$	(1,595	)
	Net income (loss) attributable to Class A and Class B common stockholders	$	4,526	$	(4,819	)	$	—	$	(4,126	)
	Basic earnings per share	$	0.05	$	(0.09	)	$	—	$	(0.09	)
	Diluted earnings per share	$	0.05	$	(0.09	)	$	—	$	(0.09	)
	Shares used in computation of earnings per share:
	Basic	87,992		53,495			49,891		46,422
	Diluted	127,603		53,495			49,891		46,422

Subsequent_Events

Subsequent Events	12 Months Ended
	Dec. 28, 2014
Subsequent Events [Abstract]
Subsequent Events	SUBSEQUENT EVENTS
	On January 23, 2015, the Company announced a restructuring plan to close the U.K. office and migrate the U.K. customers and members from the U.K.-operated site onto the North American platform, as a U.S.-operated site, consistent with the Company's strategy for Canada, Australia, and Ireland. The Company expects to incur pre-tax charges between $1.5 million and $2.5 million primarily relating to contract terminations and employee redundancy payments in fiscal year 2015. The restructuring will alter how the Company’s chief operating decision maker manages the Company’s business, makes operating decisions, and evaluates operating performance thereby resulting in one operating segment effective for the period ending March 29, 2015.
	On February 11, 2015, the Company announced that its board of directors authorized a repurchase program whereby the Company can repurchase up to $250 million of its outstanding common stock over the next 24 months. The number of shares to be repurchased under the repurchase program and the timing of any potential repurchases will depend on factors such as the Company's common stock price, economic and market conditions, alternative uses of capital, and corporate and regulatory requirements. The repurchase program may be suspended or discontinued at any time.
	On February 20, 2015, the compensation committee of the Company's board of directors approved the Company’s 2015 Executive Incentive Program, which provides the Company’s executive officers and other eligible employees the opportunity to earn semi-annual cash bonuses of between 0% to 40% (or 0% to 50% in the case of the Company's chief executive officer) of base salary based on the achievement of certain corporate and individual performance objectives, as established by the compensation committee. Achievement of the performance objectives will be determined by the compensation committee.
	* * * * * *

Summary_of_Significant_Account1

Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 28, 2014
Accounting Policies [Abstract]
Principles of Consolidation	The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany transactions and balances are eliminated in consolidation.
Fiscal Year	The Company utilizes a retail calendar whereby the fiscal year ends on the Sunday closest to December 31. Each fiscal year consists of four 13-week quarters, with one extra week added in the fourth quarter every five to six years.
Accounting Estimates	The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America (“GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Our significant estimates include assumptions related to the determination of deferred income taxes and any applicable related valuation allowances. Actual results could differ materially from those estimates.
Foreign Currency Translation	The functional currency of the Company’s U.K. subsidiary is the British Pound Sterling. Assets and liabilities of the subsidiary are translated at the exchange rate in effect at each period-end. Income statement amounts are translated at the average rate of exchange prevailing during the period. Translation adjustments arising from the use of differing exchange rates from period to period are included in accumulated other comprehensive loss within stockholders’ equity (deficit).
Cash and Cash Equivalents	Cash and cash equivalents include cash and highly-liquid investments with maturities of three months or less from the date of purchase, which are carried at amortized cost.
	The Company maintains the majority of its cash and cash equivalents in accounts with major financial institutions within the United States, generally in the form of demand and money market accounts. Deposits in these institutions may exceed federally insured limits. The Company has not experienced any losses on its deposits of cash and cash equivalents.
Short-Term Investments	The Company classifies highly-liquid investments with maturities greater than three months but less than one year as short-term investments. Short-term investments are comprised of available-for-sale securities. Available-for-sale securities are recorded at fair value, and unrealized holding gains and losses are recorded as a component of accumulated other comprehensive loss in stockholders' equity (deficit), while realized gains and losses, and other-than-temporary impairments are reported as a component of net income. For the periods presented, realized and unrealized gains and losses on investments were not material. 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. The Company assesses 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, as well as the intent and ability to hold, or plans to sell, the investment.
Accounts Receivable	The majority of sales are conducted with credit cards and accounts receivable are composed primarily of amounts due from financial institutions related to those credit card sales. The Company does not maintain an allowance for doubtful accounts as payment is typically received within a few business days after the sale. Additionally, the Company includes other receivables, which consist of receivables for amounts owed as a result of tenant improvement allowances.
Inventories	The Company’s inventories, which consist primarily of apparel, infant gear, toys and other merchandise are stated at the lower of cost or market and valued on an average cost basis. Inventory costs primarily consist of product costs from suppliers, as well as inbound shipping and handling fees. The majority of the Company’s inventories are not purchased until the Company receives a customer order and is subsequently relieved from inventories when it is delivered to the customer.
Property and Equipment	Property and equipment are stated at cost, less accumulated depreciation. Maintenance and repairs are expensed as incurred. Depreciation is calculated on a straight-line basis over the estimated useful lives of the following asset categories:
	Asset Category	Depreciation Period
	Computer equipment and capitalized software	1 to 3 years
	Leasehold improvements	Lesser of 10 years or lease term
	Furniture, machinery and other equipment	3 to 15 years
Capitalized Software	The Company capitalizes certain costs to develop its websites and internal-use software and amortizes such costs on a straight-line basis over the estimated useful life of the software once it is available for use. Capitalization of such costs begins when the preliminary project stage is completed, management with the relevant authority authorizes and commits to the funding of the software project, and it is probable that the project will be completed and the software will be used to perform the function intended.
	Capitalized software costs, net of accumulated amortization, totaled $3.6 million and $2.7 million as of December 28, 2014 and December 29, 2013, respectively, and are included in property and equipment—net in the accompanying consolidated balance sheets. Amortization expense related to capitalized software costs was $1.7 million, $1.0 million, and $0.6 million for the fiscal years ended December 28, 2014, December 29, 2013, and December 30, 2012, respectively, and is included in selling, general, and administrative expenses in the accompanying consolidated statements of operations.
Impairment of Long-Lived Assets	The Company reviews the carrying value of its long-lived assets, including property and equipment and definite-lived intangible assets, whenever events or changes in circumstances indicate that the carrying value may not be recoverable. To the extent the estimated future cash inflows attributable to the assets, less estimated future cash outflows, are less than the carrying amount, an impairment loss would be recognized.
Fair Value of Financial Instruments	The carrying amounts for the Company’s cash, cash equivalents, short-term investments, accounts receivable, accounts payable and accrued liabilities approximate fair value due to their short maturities.
Income Taxes	The Company uses the asset and liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are recognized by applying the statutory tax rates in effect in the years in which the differences between the financial reporting and tax filing bases of existing assets and liabilities are expected to reverse. Valuation allowances are established when necessary to reduce deferred tax assets to the amounts expected to be realized.
	The Company utilizes a two-step approach to recognizing and measuring uncertain income tax positions (tax contingencies). The first step is to evaluate the tax position for recognition by determining if the weight of available evidence indicates it is more likely than not that the position will be sustained on audit, including resolution of related appeals or litigation processes. The second step is to measure the tax benefit as the largest amount which is more than 50% likely of being realized upon ultimate settlement. The Company considers many factors when evaluating and estimating its tax positions and tax benefits, which may require periodic adjustments and which may not accurately forecast actual outcomes.
	The Company’s policy is to recognize interest and/or penalties related to all tax positions in income tax expense. To the extent that accrued interest and penalties do not ultimately become payable, amounts accrued will be reduced and reflected as a reduction of the overall income tax provision in the period that such determination is made.
Certain Risks and Concentrations	The Company is subject to certain risks and concentrations, including dependence on third-party technology providers and hosting services, exposure to risks associated with online commerce security, consumer credit risk, and credit card fraud, as well as the interpretation of state and local laws and regulations in regards to the collection and remittance of sales and use taxes and occupancy taxes. The Company also depends upon third-party service providers for processing customer orders.
Revenue Recognition	The Company generates net sales from sales of women's, children’s and men's apparel, children's merchandise and other product categories such as kitchen accessories and home décor, and from shipping and handling charges to the Company’s customers. The Company also generates net sales from the sale of services events, which are primarily electronic vouchers or access codes for the Company’s customers to redeem directly with the vendor. Net sales of services events have not been material to date.
	The Company recognizes revenue when the following criteria are met: (1) persuasive evidence of an arrangement exists; (2) delivery has occurred; (3) the selling price is fixed or determinable; and (4) collectability is reasonably assured. For product sales, these criteria are met when the customer orders an item through the Company’s sites via the electronic shopping cart, funds are collected from the customer and the item is fulfilled in one of the Company or third-party fulfillment centers, shipped and delivered to the customer. Revenue from product sales is generally recorded at the gross amount as the Company is the primary obligor in the arrangement with the customer, has latitude in establishing the products available for sale and the price to the customer, is responsible for ensuring the delivery of the product to the customer and assume inventory and credit risk. For services sales, these criteria are met when the customer orders an item through the Company’s sites via the electronic shopping cart, funds are collected from the customer and the voucher or access code is downloaded from the Company’s sites. Revenue from services sales is generally recorded at the net amount, or the commission earned on the voucher, as the Company is acting as an agent on behalf of the vendor. The vendor is ultimately responsible for fulfilling the customer order directly with the customer and assumes the inventory risk. To date, services revenue has not been material. The Company defers revenue when cash is collected from the customer prior to the satisfaction of the revenue recognition criteria.
	To encourage customers to purchase the Company’s products and services, the Company periodically provides incentive offers. Generally, these promotions include dollar-off and percentage-off discounts to be applied against current purchases. The Company also grants merchandise credits to participants in the Company’s referral program when the customer referral results in a sale. Merchandise credits issued through the referral program typically expire in 18 months. The Company records these discounts and merchandise credits as reductions of the sale price at the date the promotion is redeemed similar to a coupon. Additionally, the Company provides customers merchandise credits to be applied against future purchases in instances in which the customer is unsatisfied with an order. In these instances, the Company has established a sales return reserve based on the Company’s historical experience. To date, these reserves have not been significant.
	Gift cards and merchandise credits issued in lieu of a cash refund are recorded as a liability upon purchase of the gift card or issuance of the merchandise credit and do not expire. The Company reduces the liability for gift cards and merchandise credits when redeemed by a customer. If a gift card or merchandise credit is not redeemed, the Company recognizes revenue when the likelihood of its redemption becomes remote. The Company has not recognized revenue related to unredeemed gift cards and merchandise credits.
	The Company has procedures in place to detect and prevent credit card fraud as the Company has exposure to losses from fraudulent charges. Due to the insignificant losses related to chargebacks, the Company records such losses as incurred.
	Taxes collected from customers are accounted for on a net basis and are excluded from net sales.
Cost of Sales	Cost of sales consists of the purchase price of merchandise sold to customers, inbound and outbound shipping and handling costs, shipping supplies and fulfillment costs. Fulfillment costs represent those costs incurred in operating and staffing the fulfillment centers, including costs attributed to receiving, inspecting, picking, packaging and preparing customer orders for shipment. Cost of sales also includes direct and indirect labor for fulfillment center oversight, including payroll and related benefit costs and stock-based compensation expense.
Marketing	Marketing expenses are expensed as incurred and consist primarily of targeted online marketing costs, such as display advertising, keyword search campaigns, search engine optimization and social media and offline marketing costs such as television, radio and print advertising. Marketing expenses also include payroll and related benefit costs and stock-based compensation expense for employees involved in marketing activities. Marketing expenses are primarily related to growing and retaining the customer base.
Selling, General and Administrative Expenses	Selling, general and administrative expenses (“SG&A”) consist primarily of payroll and related benefit costs and stock-based compensation expense for employees involved in general corporate functions including merchandising, studio, technology and customer service, as well as costs associated with the use by these functions of facilities and equipment, including depreciation, rent and occupancy. Also included in SG&A is rent and depreciation related to fulfillment centers.
Stock-Based Compensation	The Company measures compensation cost for all stock options and restricted stock unit awards granted at their grant date estimated fair value. Stock-based compensation expense, net of estimated forfeitures, is recognized on a straight-line basis over the vesting period for each award. The fair value of stock option awards is estimated on the grant date using the Black-Scholes option valuation model. The fair value of each restricted stock unit award is based on the estimated fair market value of the Company’s common stock on the date of the award.
Recent Accounting Pronouncements Adopted	In July 2013, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update No. 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar tax Loss, or a Tax Credit Carryforward Exists ("ASU 2013-11").The amendments in this update require an unrecognized tax benefit, or a portion of an unrecognized tax benefit, to be presented in the financial statements as a reduction to a deferred tax asset for a net operating loss carryforward, a similar tax loss, or a tax credit carryforward, except as follows: To the extent a net operating loss carryforward, a similar tax loss, or a tax credit carryforward is not available at the reporting date under the tax law of the applicable jurisdiction to settle any additional income taxes that would result from the disallowance of a tax position or the tax law of the applicable jurisdiction does not require the entity to use, and the entity does not intend to use the deferred tax asset for such purpose, the unrecognized tax benefit should be presented in the financial statements as a liability and should not be combined with deferred tax assets. The assessment of whether a deferred tax asset is available is based on the unrecognized tax benefit and deferred tax asset that exist at the reporting date and should be made presuming disallowance of the tax position at the reporting date. The amendments in this update do not require new recurring disclosures. For public entities, ASU 2013-11 is effective for annual and interim periods beginning after December 15, 2013. The Company adopted ASU 2013-11 in the first quarter of 2014 and it did not have a material impact on the Company's consolidated financial statements or related disclosures.
	Recent accounting guidance not yet adopted
	In May 2014, the FASB issued an Accounting Standard Update No. 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”) amending revenue recognition guidance and requiring 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. The guidance is effective for annual and interim reporting periods beginning after December 15, 2016, with early adoption prohibited. The Company is currently evaluating the impact ASU 2014-09 will have on its consolidated financial statements.
	In August 2014, the FASB issued ASU 2014-15 related to going concern. The new guidance explicitly requires that management assess an entity's ability to continue as a going concern and may require additional detailed disclosures. ASU 2014-15 is effective for annual periods beginning after December 15, 2016 and interim periods within those annual periods. Though permitted, the Company does not plan to early adopt. The Company does not believe that this standard will have a significant impact on its consolidated financial statements.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 28, 2014
Accounting Policies [Abstract]
Property and Equipment	Depreciation is calculated on a straight-line basis over the estimated useful lives of the following asset categories:
	Asset Category	Depreciation Period
	Computer equipment and capitalized software	1 to 3 years
	Leasehold improvements	Lesser of 10 years or lease term
	Furniture, machinery and other equipment	3 to 15 years
	The balance of property and equipment—net is as follows:
		December 28,			December 29,
		2014			2013
		(in thousands)
	Computer equipment and capitalized software	$	24,111		$	15,963
	Leasehold improvements	26,166			1,272
	Furniture, machinery and other equipment	49,824			12,224
	Work in progress	1,261			5,228
	Less: accumulated depreciation and amortization	(22,464		)	(10,074		)
	Total property and equipment, net	$	78,898		$	24,613

Accrued_Expenses_Tables

Accrued Expenses (Tables)	12 Months Ended
	Dec. 28, 2014
Payables and Accruals [Abstract]
Schedule of accrued liabilities	Accrued expenses consist of the following:
		December 28,		December 29,
		2014		2013
		(in thousands)
	Accrued payroll	$	12,607	$	5,327
	Accrued marketing	6,655		3,595
	Accrued shipping	10,063		15,186
	Other accrued expenses	10,149		6,665
	Total accrued expenses	$	39,474	$	30,773

Property_and_Equipment_Tables

Property and Equipment (Tables)	12 Months Ended
	Dec. 28, 2014
Property, Plant and Equipment [Abstract]
Property and Equipment	Depreciation is calculated on a straight-line basis over the estimated useful lives of the following asset categories:
	Asset Category	Depreciation Period
	Computer equipment and capitalized software	1 to 3 years
	Leasehold improvements	Lesser of 10 years or lease term
	Furniture, machinery and other equipment	3 to 15 years
	The balance of property and equipment—net is as follows:
		December 28,			December 29,
		2014			2013
		(in thousands)
	Computer equipment and capitalized software	$	24,111		$	15,963
	Leasehold improvements	26,166			1,272
	Furniture, machinery and other equipment	49,824			12,224
	Work in progress	1,261			5,228
	Less: accumulated depreciation and amortization	(22,464		)	(10,074		)
	Total property and equipment, net	$	78,898		$	24,613

Commitment_and_Contingencies_T

Commitment and Contingencies (Tables)	12 Months Ended
	Dec. 28, 2014
Commitments and Contingencies Disclosure [Abstract]
Schedule of future minimum payments under noncancelable operating leases	Future minimum payments under noncancelable operating leases as of December 28, 2014 are as follows:
	Fiscal Years Ending	Amount
		(in thousands)
	2015	$	15,370
	2016	16,464
	2017	15,492
	2018	14,962
	2019	15,392
	Thereafter	66,503
	Total	$	144,183

Stockholders_Equity_Deficit_Ta

Stockholders' Equity (Deficit) (Tables)	12 Months Ended
	Dec. 28, 2014
Equity [Abstract]
Schedule of Assumptions for Fair Value of Stock Options	The fair value of each stock option is estimated on the grant date with the following weighted-average assumptions:
		Year Ended
		December 28,				December 29,				December 30,
		2014				2013				2012
	Expected term (years)	6.1				6.66				5.98
	Expected volatility	54.7		%		50.9		%		61.7		%
	Expected dividend yield	—		%		—		%		—		%
	Risk-free interest rate	1.9		%		1.3		%		1		%
	Weighted average grant-date fair value of stock options granted	$	21.41			$	6.75			$	4.1
Allocation of recognized period costs	The following table presents the effects of stock-based compensation on the consolidated statements of operations during the periods presented:
		Year Ended
		December 28,				December 29,				December 30,
		2014				2013				2012
		(in thousands)
	Cost of sales	$	210			$	70			$	26
	Marketing expenses	790				327				142
	Selling, general and administrative expenses	13,548				7,380				1,097
	Total stock-based compensation expense	$	14,548			$	7,777			$	1,265
Schedule of Share-based Compensation, Stock Options, Additional Information [Table Text Block]	The following table summarizes additional information about stock options outstanding as of December 28, 2014:
		Outstanding									Outstanding and Vested
					Weighted Average
	Range of Exercise Price	Options			Exercise				Remaining		Options		Weighted
					Price				Contractual				Average
									Life				Exercise Price
									(in Years)
	$0.028 - $0.312	1,735,762			$	0.26			5.91		1,716,878		$	0.26
	$0.717 - $7.44	1,043,938			$	4.47			6.86		848,034		$	4.11
	$7.48 - $10.28	7,778,683			$	9.6			8.24		6,371,090		$	9.89
	$13.44 - $41.43	1,153,776			$	20.95			8.86		308,922		$	18.36
	$41.79 - $53.89	366,788			$	43.79			9.16		—		$	—
	Total	12,078,947									9,244,924
Schedule of stock options activity	The table summarizes stock option activity as follows:
		Number of			Weighted				Weighted		Total
		Shares			Average				Average		Intrinsic
		Underlying			Exercise				Remaining		Value
		Options			Price				Contractual
									Term
									(in Years)
		(in thousands, except price, shares and years)
	Outstanding at December 29, 2013	13,938,487			$	7.4			8.56		$	462,558
	Granted	681,840			40.87
	Exercised	(2,062,226	)		1.92
	Canceled	(479,154	)		14.88
	Outstanding at December 28, 2014	12,078,947			9.93				7.87		172,655
	Vested and expected to vest at December 28, 2014	11,873,058			9.77				7.85		170,874
	Exercisable at December 28, 2014	9,244,924			7.85				7.72		142,630
Schedule RSU Award activity	The table summarizes RSU awards activity as follows:
		Number of Shares Underlying RSUs			Weighted Average Grant-Date Fair Value per RSU
	Outstanding at December 29, 2013	—			$	—
	Granted	379,888			35.49
	Vested	(675	)		34.36
	Forfeited	(14,083	)		36.23
	Outstanding at December 28, 2014	365,130			$	35.47

Net_Income_Loss_Per_Share_Tabl

Net Income (Loss) Per Share (Tables)	12 Months Ended
	Dec. 28, 2014
Earnings Per Share [Abstract]
Schedule of earnings per share calculation	The following table presents the calculation of basic and diluted net income (loss) per common share:
		Year Ended
		December 28,			December 29,			December 30,
		2014			2013			2012
		(in thousands, except share and per share amounts)
	Numerator
	Net income (loss)	$	14,892		$	12,908		$	(10,335	)
	Less: Accretion of convertible redeemable preferred stock	—			(8,975		)	(4,375		)
	Less: Distributed earnings attributable to participating securities	—			—			(32,112		)
	Less: Undistributed earnings attributable to participating securities	—			(3,933		)	—
	Net income (loss) attributable to Class A and Class B common stockholders	$	14,892		$	—		$	(46,822	)
	Denominator
	Weighted average shares used to compute basic net income (loss) per Class A and Class B common share	124,679,716			59,450,186			37,976,724
	Effect of potentially dilutive securities:
	Stock options	7,615,037			—			—
	Restricted stock unit awards	22,604			—			—
	Weighted average shares used to compute diluted net income (loss) per Class A and Class B common share	132,317,357			59,450,186			37,976,724
	Net income (loss) per share attributable to Class A and Class B common stockholders—basic	$	0.12		$	—		$	(1.23	)
	Net income (loss) per share attributable to Class A and Class B common stockholders—diluted	$	0.11		$	—		$	(1.23	)
Schedule of antidilutive securities excluded from computation of earnings per share	The following have been excluded from the computation of basic and diluted net income (loss) per share attributable to Class A and Class B common stockholders as their effect would have been antidilutive:
		Year Ended
		December 28,		December 29,			December 30,
		2014		2013			2012
	Convertible preferred shares	—		53,184,953			55,827,571
	Unvested restricted common shares	—		3,644,546			16,468,775
	Stock options	403,742		13,938,487			7,430,501
	Restricted stock unit awards	137,110		—			—
	Total	540,852		70,767,986			79,726,847

Segment_Information_Tables

Segment Information (Tables)	12 Months Ended
	Dec. 28, 2014
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	Information on reportable segments and reconciliation to consolidated net income (loss) before provision for income taxes is as follows:
		Year Ended
		December 28,			December 29,			December 30,
		2014			2013			2012
		(in thousands)
	North America
	Net sales	$	1,181,501		$	681,826		$	326,349
	Operating income (loss)	20,715			17,173			(6,072		)
	Intersegment expense	(4,951		)	(4,093		)	(4,571		)
	Total segment operating income (loss)	15,764			13,080			(10,643		)
	U.K.
	Net sales	18,578			13,883			4,891
	Intersegment sales	4,951			4,093			4,571
	Total net sales	23,529			17,976			9,462
	Segment operating income (loss)	$	(34	)	$	(51	)	$	89
	Consolidated
	Net sales
	Total sales for reportable segments	$	1,205,030		$	699,802		$	335,811
	Elimination of intersegment sales	(4,951		)	(4,093		)	(4,571		)
	Total consolidated net sales	$	1,200,079		$	695,709		$	331,240
	Net income (loss) before provision for income taxes
	Total operating income (loss) for reportable segments	$	15,730		$	13,029		$	(10,554	)
	Interest income (expense)—net	317			136			43
	Other income (expense)—net	(46		)	99			176
	Net income (loss) before provision for income taxes	$	16,001		$	13,264		$	(10,335	)

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 28, 2014
Income Tax Disclosure [Abstract]
Changes in Amount of Unrecognized Tax Benefits	A reconciliation of the change in amount of gross unrecognized income tax benefits for the prior three years is as follows:
		Year Ended
		December 28,				December 29,				December 30,
		2014				2013				2012
		(in thousands)
	Balance at the beginning of the year	$	377			$	—			$	—
	Increase related to prior period tax positions	(40		)		172				—
	Increase related to current period tax positions	369				205				—
	Balance at the end of the year	$	706			$	377			$	—
Components of Income (Loss) before Provision for Income Taxes	The components of income (loss) before provision for income taxes are as follows:
		Year Ended
		December 28,				December 29,				December 30,
		2014				2013				2012
		(in thousands)
	U.S.	$	16,001			$	13,266			$	(10,401	)
	Foreign	—				(2		)		66
	Income before income taxes	$	16,001			$	13,264			$	(10,335	)
Schedule of Components of Income Tax Expense	Income taxes have been provided as follows:
		Year Ended
		December 28,				December 29,				December 30,
		2014				2013				2012
		(in thousands)
	Current tax expense:
	Federal	$	546			$	356			$	—
	State and Local	—				—				—
	Foreign	—				—				—
	Current tax expense	546				356				—
	Deferred tax expense:
	Federal	537				—				—
	State and Local	26				—				—
	Foreign	—				—				—
	Deferred tax expense	563				—				—
	Provision for income taxes	$	1,109			$	356			$	—
Reconciliation of Income Tax Computed at Federal Statutory Rates to the Reported Provisions for Income Taxes	Reconciliation of income tax computed at federal statutory rates to the reported provisions for income taxes is as follows:
		Year ended
		December 28,			December 29,			December 30,
		2014			2013			2012
	Federal statutory rate	35	%		35	%		(34.0	)%
	Effect of:
	State and local income tax	—			—			(1.0	)
	Non-deductible expenses	0.3			0.2			(0.1	)
	R&D tax credit generated in current year	(5.4	)		(2.3	)		(4.6	)
	Stock-based compensation	2			5.6			4.2
	Other	0.2			0.1			0.4
	Valuation allowance	(25.1	)		(35.9	)		35.1
	Total	7	%		2.7	%		—	%
Schedule of Deferred Tax Assets and Liabilities	Deferred tax assets and liabilities are summarized as follows:
		As Of
		December 28,				December 29,
		2014				2013
		(in thousands)
	Deferred tax assets:
	Tax loss carryforwards	$	18			$	2,402
	Returns and accruals	2,053				1,305
	Deferred rent	7,263				817
	Inventories	787				746
	Stock-based compensation	6,316				2,027
	Tax-credit carryforwards	1,376				1,236
	Other	52				—
	Deferred tax assets	17,865				8,533
	Deferred tax liabilities:
	Property and equipment	(18,041		)		(4,115		)
	Prepaid expenses and other current assets	(356		)		(400		)
	Unrealized foreign exchange gain	—				(34		)
	Deferred tax liabilities	(18,397		)		(4,549		)
	Valuation allowance	(31		)		(3,984		)
	Deferred tax asset (liability), net	$	(563	)		$	—
	Current asset (liability), net	$	17,827			$	2,675
	Noncurrent asset (liability), net	(18,390		)		(2,675		)
	Deferred tax asset (liability), net	$	(563	)		$	—

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 28, 2014
Fair Value Disclosures [Abstract]
Fair Value, Assets Measured on Recurring Basis	The following tables summarize the Company's assets that are measured at fair value on a recurring basis, by level, within the fair value hierarchy as of December 28, 2014 and December 29, 2013:
		28-Dec-14
		Total		Level 1		Level 2		Level 3
		(in thousands)
	Cash equivalents:
	Money market funds	$	3,015	$	3,015	$	—	$	—
	Short-term investments:
	Commercial paper	131,528		—		131,528		—
	Total	$	134,543	$	3,015	$	131,528	$	—
		December 29, 2013
		Total		Level 1		Level 2		Level 3
		(in thousands)
	Cash equivalents:
	Money market funds	$	18,019	$	18,019	$	—	$	—
	Short-term investments:
	Commercial paper	18,014		—		18,014		—
	Total	$	36,033	$	18,019	$	18,014	$	—

Quarterly_Financial_Informatio1

Quarterly Financial Information (Tables)	12 Months Ended
	Dec. 28, 2014
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	Unaudited quarterly results are as follows:
		Quarters Ended
		Dec. 28, 2014		Sept. 28, 2014*			Jun. 29, 2014		Mar. 30, 2014
		(in thousands, except per share amounts)
	Net sales	$	391,349	$	285,836		$	285,013	$	237,881
	Gross profit	101,067		78,689			80,956		63,734
	Income (loss) from operations	11,669		(663		)	7,675		(2,951		)
	Net income (loss) before provision for income taxes	11,690		(495		)	7,756		(2,950		)
	Provision for income taxes	809		300			—		—
	Net income (loss)	$	10,881	$	(795	)	$	7,756	$	(2,950	)
	Net income (loss) attributable to Class A and Class B common stockholders	$	10,881	$	(795	)	$	7,756	$	(2,950	)
	Basic earnings per share	$	0.09	$	(0.01	)	$	0.06	$	(0.02	)
	Diluted earnings per share	$	0.08	$	(0.01	)	$	0.06	$	(0.02	)
	Shares used in computation of earnings per share:
	Basic	125,525		124,985			124,424		123,879
	Diluted	131,036		124,985			133,067		123,879
	*Includes the previously disclosed out-of-period correction of $2.8 million. The net impact of the adjustment was an increase to net sales of $2.8 million and a decrease to deferred revenue of the same amount.
		Quarters Ended
		Dec. 29, 2013		Sept. 29, 2013			Jun. 30, 2013		Mar. 31, 2013
		(in thousands, except per share amounts)
	Net sales	$	257,033	$	166,655		$	145,009	$	127,012
	Gross profit	68,375		44,501			43,903		36,612
	Income (loss) from operations	12,922		(2,283		)	4,003		(1,613		)
	Net income (loss) before provision for income taxes	13,109		(2,251		)	4,001		(1,595		)
	Provision for income taxes	356		—			—		—
	Net income (loss)	$	12,753	$	(2,251	)	$	4,001	$	(1,595	)
	Net income (loss) attributable to Class A and Class B common stockholders	$	4,526	$	(4,819	)	$	—	$	(4,126	)
	Basic earnings per share	$	0.05	$	(0.09	)	$	—	$	(0.09	)
	Diluted earnings per share	$	0.05	$	(0.09	)	$	—	$	(0.09	)
	Shares used in computation of earnings per share:
	Basic	87,992		53,495			49,891		46,422
	Diluted	127,603		53,495			49,891		46,422

The_Company_and_Basis_of_Prese1

The Company and Basis of Presentation (Details) (USD $)	Dec. 28, 2014	Dec. 29, 2013
In Thousands, unless otherwise specified
Reclassification of merchandise deposits to prepaid expenses and other current assets	$8,165	$4,192
Restatement Adjustment [Member]
Reclassification of merchandise deposits to prepaid expenses and other current assets		$500

Summary_of_Significant_Account3

Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
Property, Plant and Equipment [Line Items]
Program merchandise credit expiration period	0 years 18 months 0 days
Property and equipment, net
Property, Plant and Equipment [Line Items]
Capitalized software costs, net of accumulated amortization	$3.60	$2.70
Minimum [Member] | Computer equipment and capitalized software[Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	1 year
Minimum [Member] | Furniture, machinery and other equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Maximum [Member] | Computer equipment and capitalized software[Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Maximum [Member] | Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	10 years
Maximum [Member] | Furniture, machinery and other equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	15 years
Selling, General and Administrative Expenses [Member]
Property, Plant and Equipment [Line Items]
Amortization expense related to capitalized software costs	$1.70	$1	$0.60

Accrued_Expenses_Details

Accrued Expenses (Details) (USD $)	Dec. 28, 2014	Dec. 29, 2013
In Thousands, unless otherwise specified
Payables and Accruals [Abstract]
Accrued payroll	$12,607	$5,327
Accrued marketing	6,655	3,595
Accrued shipping	10,063	15,186
Other accrued expenses	10,149	6,665
Total accrued expenses	$39,474	$30,773

Property_and_Equipment_Details

Property and Equipment (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
Property, Plant and Equipment [Line Items]
Less: accumulated depreciation and amortization	($22,464)	($10,074)
Total property and equipment, net	78,898	24,613
Depreciation and amortization	13,100	6,240	3,369
Computer equipment and capitalized software[Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	24,111	15,963
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	26,166	1,272
Furniture, Machinery and Other Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	49,824	12,224
Work in progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$1,261	$5,228

Commitment_and_Contingencies_D

Commitment and Contingencies (Details) (USD $)	12 Months Ended
	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
Loss Contingencies [Line Items]
Rental expense	$8,300,000	$5,900,000	$4,600,000
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2015	15,370,000
2016	16,464,000
2017	15,492,000
2018	14,962,000
2019	15,392,000
Thereafter	66,503,000
Total	$144,183,000
State Sales and Use Tax Claim [Member]
Loss Contingencies [Line Items]
Number of actual or threatened claims	0

Credit_Facility_Details

Credit Facility (Details) (Revolving Credit Facility [Member], USD $)	1 Months Ended
	Jan. 31, 2014
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$50,000,000
Undrawn commitment fee percentage	0.18%
Base Rate [Member]
Line of Credit Facility [Line Items]
Stated rate	1.50%
Federal Funds Rate [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
Eurodollar [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.00%
London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.50%

Retirement_Plan_Details

Retirement Plan (Details) (USD $)	12 Months Ended
	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
Compensation and Retirement Disclosure [Abstract]
Costs incurred relating to matching contributions	$600,000	$0	$0

Stockholders_Equity_Deficit_Na

Stockholders' Equity (Deficit) - Narrative (Details) (USD $)	12 Months Ended			1 Months Ended
	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012	Nov. 30, 2013	Oct. 26, 2009
	class
Class of Stock [Line Items]
Underwriting discounts and offering expenses		$3,318,000
Preferred stock, shares authorized (in shares)	2,000,000	2,000,000
Number of classes of common stock	2
Stock-based compensation expense	14,548,000	7,777,000	1,265,000
Early exercisable stock options	4,761,744	5,462,661
IPO [Member]
Class of Stock [Line Items]
Net proceeds from the offering, net of underwriting discounts and offering expenses				147,500,000
Underwriting discounts and offering expenses				3,300,000
Common Class A [Member]
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	500,000,000	500,000,000
Shares outstanding	61,327,351	13,225,000
Common Stock, Voting Rights, Votes Per Share	1
Common Class A [Member] | IPO [Member]
Class of Stock [Line Items]
Issuance of common stock (in shares)				7,334,125
Share Price				$22
Sale of stock, number of shares sold by stockholders				5,890,875
Common Class B [Member]
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	275,000,000	275,000,000
Shares outstanding	64,115,226	110,159,235
Common Stock, Voting Rights, Votes Per Share	10
Restricted Stock Purchase Agreement [Member] | Common Class B [Member] | Restricted Stock [Member]
Class of Stock [Line Items]
Share Price					$0.00
Vesting period of awards	4 years
Number of shares vested	52,812,500	52,792,969
Number of shares expected to vest		19,531
Stock-based compensation expense	$0
Restricted Stock Purchase Agreement [Member] | Share-based Compensation Award, Tranche One [Member] | Common Class B [Member] | Restricted Stock [Member]
Class of Stock [Line Items]
Percentage vested on first anniversary after grant date	25.00%
Restricted Stock Purchase Agreement [Member] | Share-based Compensation Award, Tranche Two [Member] | Common Class B [Member] | Restricted Stock [Member]
Class of Stock [Line Items]
Vesting period of awards	3 years
Holder Option [Member] | Common Class A [Member]
Class of Stock [Line Items]
Class B to Class A conversion	1
Stock Transfer [Member] | Common Class A [Member]
Class of Stock [Line Items]
Class B to Class A conversion	1

Stockholders_Equity_Deficit_St

Stockholders' Equity (Deficit) - Stock-Based Compensation Expense (Details) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 28, 2014	Jan. 01, 2012	Dec. 29, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation cost	49.7
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average remaining contractual term	4 years 10 months 6 days
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average remaining contractual term	4 years 7 months 28 days
2009 Plan [Member] | Stock options [Member] | Common Class B [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued for the exercise of stock options		1,439,627
Shares early exercised		473,958
Unvested portion of early exercised shares	0		63,151

Stockholders_Equity_Deficit_Eq

Stockholders' Equity (Deficit) - Equity Incentive Plans (Details) (USD $)	12 Months Ended
	Dec. 28, 2014
	equity_incentive_plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity incentive plans	2
Annual increase in number of shares reserved for issuance, maximum	4.00%
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of shares available	18,122,045
Vesting period of awards	4 years 10 months 6 days
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of shares available	10,300,000
Vesting period of awards	4 years 7 months 28 days
2009 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of shares available for issuance	0
2009 Equity Incentive Plan [Member] | Common Class B [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance of equity incentive awards	18,105,313
2013 Equity Incentive Plan [Member] | Common Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance of equity incentive awards	11,795,185
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized	1,627,200
Maximum number of shares issuable	27,610,562
2013 Equity Incentive Plan [Member] | Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period of awards	10 years
2013 Equity Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of awards	5 years
Expiration period of awards	10 years
Share-based Compensation Award, Tranche One [Member] | 2013 Equity Incentive Plan [Member] | Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage vested on first anniversary after grant date	25.00%
Share-based Compensation Award, Tranche Two [Member] | 2013 Equity Incentive Plan [Member] | Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of awards	3 years

Stockholders_Equity_Deficit_We

Stockholders' Equity (Deficit) - Weighted Average Assumptions (Details) (Stock options [Member], USD $)	12 Months Ended
	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
Stock options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (years)	6 years 1 month 7 days	6 years 7 months 29 days	5 years 11 months 23 days
Expected volatility	54.70%	50.90%	61.70%
Expected dividend yield	0.00%	0.00%	0.00%
Risk-free interest rate	1.90%	1.30%	1.00%
Weighted average grant-date fair value of stock options granted (in usd per share)	$21.41	$6.75	$4.10

Stockholders_Equity_Deficit_Al

Stockholders' Equity (Deficit) - Allocation of Recognized Period Costs (Details) (USD $)	12 Months Ended
	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$14,548,000	$7,777,000	$1,265,000
Cost of Sales [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	210,000	70,000	26,000
Marketing Expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	790,000	327,000	142,000
Selling, General and Administrative Expenses [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$13,548,000	$7,380,000	$1,097,000

Stockholders_Equity_Deficit_St1

Stockholders' Equity (Deficit) - Stock Options Additional Information (Details) (USD $)	12 Months Ended
	Dec. 28, 2014
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding (in shares)	12,078,947
Options outstanding and vested (in shares)	9,244,924
$0.028 - $0.312 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding (in shares)	1,735,762
Options outstanding, weighted average exercise price (in usd per share)	$0.26
Options outstanding, remaining contractual life (in years)	5 years 10 months 28 days
Options outstanding and vested (in shares)	1,716,878
Options outstanding and vested, weighted average exercise price (in usd per share)	$0.26
$0.717 - $7.44 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding (in shares)	1,043,938
Options outstanding, weighted average exercise price (in usd per share)	$4.47
Options outstanding, remaining contractual life (in years)	6 years 10 months 11 days
Options outstanding and vested (in shares)	848,034
Options outstanding and vested, weighted average exercise price (in usd per share)	$4.11
$7.48 - $10.28 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding (in shares)	7,778,683
Options outstanding, weighted average exercise price (in usd per share)	$9.60
Options outstanding, remaining contractual life (in years)	8 years 2 months 27 days
Options outstanding and vested (in shares)	6,371,090
Options outstanding and vested, weighted average exercise price (in usd per share)	$9.89
$13.44 - $41.43 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding (in shares)	1,153,776
Options outstanding, weighted average exercise price (in usd per share)	$20.95
Options outstanding, remaining contractual life (in years)	8 years 10 months 11 days
Options outstanding and vested (in shares)	308,922
Options outstanding and vested, weighted average exercise price (in usd per share)	$18.36
$41.79 - $53.89 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding (in shares)	366,788
Options outstanding, weighted average exercise price (in usd per share)	$43.79
Options outstanding, remaining contractual life (in years)	9 years 1 month 29 days
Options outstanding and vested (in shares)	0
Options outstanding and vested, weighted average exercise price (in usd per share)	$0
Minimum [Member] | $0.028 - $0.312 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in usd per share)	$0.03
Minimum [Member] | $0.717 - $7.44 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in usd per share)	$0.72
Minimum [Member] | $7.48 - $10.28 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in usd per share)	$7.48
Minimum [Member] | $13.44 - $41.43 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in usd per share)	$13.44
Minimum [Member] | $41.79 - $53.89 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit (in usd per share)	$41.79
Maximum [Member] | $0.028 - $0.312 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, upper limit (in usd per share)	$0.31
Maximum [Member] | $0.717 - $7.44 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, upper limit (in usd per share)	$7.44
Maximum [Member] | $7.48 - $10.28 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, upper limit (in usd per share)	$10.28
Maximum [Member] | $13.44 - $41.43 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, upper limit (in usd per share)	$41.43
Maximum [Member] | $41.79 - $53.89 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, upper limit (in usd per share)	$53.89

Stockholders_Equity_Deficit_St2

Stockholders' Equity (Deficit) - Stock Option Activity (Details) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 28, 2014	Dec. 29, 2013	Sep. 28, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, Beginning Balance (in shares)	13,938,487
Granted (in shares)	681,840
Exercised (in shares)	-2,062,226
Canceled (in shares)	-479,154
Outstanding, Ending Balance (in shares)	12,078,947	13,938,487
Vested and expected to vest (in shares)	11,873,058
Exercisable (in shares)	9,244,924
Share-based Compensation Arrangement by Share-based Payment Award, Options, Weighted Average Exercise Price [Abstract]
Weighted Average Exercise Price, Outstanding, Beginning Balance (in dollars per share)	$7.40
Weighted Average Exercise Price, Granted (in dollars per share)	$40.87
Weighted Average Exercise Price, Exercised (in dollars per share)	$1.92
Weighted Average Exercise Price, Canceled (in dollars per share)	$14.88
Weighted Average Exercise Price, Outstanding, Ending Balance (in dollars per share)	$9.93	$7.40
Weighted Average Exercise Price, Vested and expected to vest (in dollars per share)	$9.77
Weighted Average Exercise Price, Exercisable (in dollars per share)	$7.85
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted Average Remaining Contractual Term, Outstanding	7 years 10 months 15 days	8 years 6 months 23 days
Weighted Average Remaining Contractual Term, Vested and expected to vest	7 years 10 months 7 days
Weighted Average Remaining Contractual Term, Exercisable	7 years 8 months 21 days
Total Intrinsic Value, Outstanding		$462,558	$172,655
Total Intrinsic Value, Vested and expected to vest			170,874
Total Intrinsic Value, Exercisable			$142,630

Stockholders_Equity_Deficit_RS

Stockholders' Equity (Deficit) - RSU Activity (Details) (Restricted Stock Units (RSUs) [Member], USD $)	12 Months Ended
	Dec. 28, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost relating to unvested RSUs	$10,300,000
Weighted average remaining contractual term	4 years 7 months 28 days
2013 Equity Plan
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding (in shares)	0
Granted (in shares)	379,888
Vested (in shares)	-675
Forfeited (in shares)	-14,083
Outstanding (in shares)	365,130
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Grant Date Fair Value - Outstanding (in dollars per share)	$0
Weighted Average Grant Date Fair Value - Granted (in dollars per share)	$35.49
Weighted Average Grant Date Fair Value - Vested (in dollars per share)	$34.36
Weighted Average Grant Date Fair Value - Forfeited (in dollars per share)	$36.23
Weighted Average Grant Date Fair Value - Outstanding (in dollars per share)	$35.47

Net_Income_Loss_Per_Share_Deta

Net Income (Loss) Per Share (Details) (USD $)	3 Months Ended								12 Months Ended			1 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 28, 2014	Sep. 28, 2014	Jun. 29, 2014	Mar. 30, 2014	Dec. 29, 2013	Sep. 29, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012	Nov. 30, 2013
Calculation of Basic and Diluted Income (Loss) Per Share)
NET INCOME (LOSS)	$10,881	($795)	$7,756	($2,950)	$12,753	($2,251)	$4,001	($1,595)	$14,892	$12,908	($10,335)
Less: Accretion of convertible redeemable preferred stock									0	-8,975	-4,375
Less: Distributed earnings attributable to participating securities									0	0	-32,112
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic									0	-3,933	0
Net income (loss) attributable to Class A and Class B common stockholders	$10,881	($795)	$7,756	($2,950)	$4,526	($4,819)	$0	($4,126)	$14,892	$0	($46,822)
Weighted average shares used to compute basic net income (loss) per Class A and Class B common share (in shares)	125,525,000	124,985,000	124,424,000	123,879,000	87,992,000	53,495,000	49,891,000	46,422,000	124,679,716	59,450,186	37,976,724
Effect of potentially dilutive securities:
Stock options (in shares)									7,615,037	0	0
Restricted stock units (in shares)									22,604	0	0
Weighted average shares used to compute diluted net income (loss) per Class A and Class B common share (in shares)	131,036,000	124,985,000	133,067,000	123,879,000	127,603,000	53,495,000	49,891,000	46,422,000	132,317,357	59,450,186	37,976,724
Net income (loss) per share attributable to Class A and Class B common stockholders--basic (in dollars per share)	$0.09	($0.01)	$0.06	($0.02)	$0.05	($0.09)	$0	($0.09)	$0.12	$0	($1.23)
Net income (loss) per share attributable to Class A and Class B common stockholders—diluted (in dollars per share)	$0.08	($0.01)	$0.06	($0.02)	$0.05	($0.09)	$0	($0.09)	$0.11	$0	($1.23)
Common Class B [Member]
Class of Stock [Line Items]
Outstanding shares of preferred stock automatically converted to shares of Class B Common Stock, upon Closing of Initial Public Offering												60,621,233
Common Stock, Voting Rights, Votes Per Share									10
Common Class A [Member]
Class of Stock [Line Items]
Common Stock, Voting Rights, Votes Per Share									1

Net_Income_Loss_Per_Share_Sche

Net Income (Loss) Per Share (Schedule of Antidilutive Securities) (Details)	12 Months Ended
	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	540,852	70,767,986	79,726,847
Convertible preferred shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	0	53,184,953	55,827,571
Unvested restricted common shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	0	3,644,546	16,468,775
Stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	403,742	13,938,487	7,430,501
Restricted stock unit awards [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	137,110	0	0

Segment_Information_Details

Segment Information (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 28, 2014	Sep. 28, 2014	Jun. 29, 2014	Mar. 30, 2014	Dec. 29, 2013	Sep. 29, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
									Segment
Segment Reporting [Abstract]
Number of reportable segments									2
Segment Reporting Information [Line Items]
Net sales	$391,349	$285,836	$285,013	$237,881	$257,033	$166,655	$145,009	$127,012	$1,200,079	$695,709	$331,240
Operating (loss) income	11,669	-663	7,675	-2,951	12,922	-2,283	4,003	-1,613	15,730	13,029	-10,554
Interest income (expense)-net									317	136	43
Other income (expense)-net									-46	99	176
Net income (loss) before provision for income taxes	11,690	-495	7,756	-2,950	13,109	-2,251	4,001	-1,595	16,001	13,264	-10,335
North America [Member]
Segment Reporting Information [Line Items]
Operating (loss) income									15,764	13,080	-10,643
United Kingdom [Member]
Segment Reporting Information [Line Items]
Net sales									23,529	17,976	9,462
Operating (loss) income									-34	-51	89
Segment Reconciling Items [Member] | North America [Member]
Segment Reporting Information [Line Items]
Net sales									1,181,501	681,826	326,349
Operating (loss) income									20,715	17,173	-6,072
Segment Reconciling Items [Member] | United Kingdom [Member]
Segment Reporting Information [Line Items]
Net sales									18,578	13,883	4,891
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Net sales									-4,951	-4,093	-4,571
Intersegment Eliminations [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating (loss) income									-4,951	-4,093	-4,571
Intersegment Eliminations [Member] | United Kingdom [Member]
Segment Reporting Information [Line Items]
Net sales									4,951	4,093	4,571
Reportable Segments [Member]
Segment Reporting Information [Line Items]
Net sales									1,205,030	699,802	335,811
Operating (loss) income									$15,730	$13,029	($10,554)

Income_Taxes_Narrative_Details

Income Taxes - Narrative (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 28, 2014	Sep. 28, 2014	Jun. 29, 2014	Mar. 30, 2014	Dec. 29, 2013	Sep. 29, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
Operating Loss Carryforwards [Line Items]
Tax provisions	$809,000	$300,000	$0	$0	$356,000	$0	$0	$0	$1,109,000	$356,000	$0
Release of deferred tax asset valuation allowance									3,900,000
Excess tax benefit from stock-based compensation									280,000
Unrecognized tax benefits	700,000								700,000
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	33,900,000								33,900,000
Non-US [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	500,000								500,000
Research Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	2,400,000								2,400,000
Alternative Tax Credits [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	$400,000								$400,000

Income_Taxes_Components_of_Inc

Income Taxes - Components of Income (Loss) before Provision for Income Taxes (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 28, 2014	Sep. 28, 2014	Jun. 29, 2014	Mar. 30, 2014	Dec. 29, 2013	Sep. 29, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
Income Tax Disclosure [Abstract]
Income (loss) from continuing operations before income taxes, U.S.									$16,001	$13,266	($10,401)
Income (Loss) from continuing operations before income taxes, foreign									0	-2	66
NET INCOME (LOSS) BEFORE PROVISION FOR INCOME TAXES	$11,690	($495)	$7,756	($2,950)	$13,109	($2,251)	$4,001	($1,595)	$16,001	$13,264	($10,335)

Income_Taxes_Schedule_of_Incom

Income Taxes - Schedule of Income Tax Provision (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 28, 2014	Sep. 28, 2014	Jun. 29, 2014	Mar. 30, 2014	Dec. 29, 2013	Sep. 29, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
Income Tax Disclosure [Abstract]
Current tax expense, federal									$546	$356	$0
Current tax expense, state and local									0	0	0
Current tax expense, foreign									0	0	0
Current tax expense									546	356	0
Deferred tax expense, federal									537	0	0
Deferred tax expense, state and local									26	0	0
Deferred tax expense, foreign									0	0	0
Deferred income taxes									563	0	0
PROVISION FOR INCOME TAXES	$809	$300	$0	$0	$356	$0	$0	$0	$1,109	$356	$0

Income_Taxes_Federal_Statutory

Income Taxes - Federal Statutory Rate Reconciliation (Details)	12 Months Ended
	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory rate	35.00%	35.00%	-34.00%
State and local income tax	0.00%	0.00%	-1.00%
Non-deductible expenses	0.30%	0.20%	-0.10%
R&D tax credit generated in current year	-5.40%	-2.30%	-4.60%
Stock-based compensation	2.00%	5.60%	4.20%
Other	0.20%	0.10%	0.40%
Valuation allowance	-25.10%	-35.90%	35.10%
Total	7.00%	2.70%	0.00%

Income_Taxes_Deferred_Tax_Asse

Income Taxes - Deferred Tax Assets and Liabilities (Details) (USD $)	Dec. 28, 2014	Dec. 29, 2013
In Thousands, unless otherwise specified
Deferred tax assets:
Tax loss carryforwards	$18	$2,402
Returns and accruals	2,053	1,305
Deferred rent	7,263	817
Inventories	787	746
Stock-based compensation	6,316	2,027
Tax-credit carryforwards	1,376	1,236
Other	52	0
Deferred tax assets	17,865	8,533
Deferred Tax Liabilities, Gross [Abstract]
Property and equipment	-18,041	-4,115
Prepaid expenses and other current assets	-356	-400
Unrealized foreign exchange gain	0	-34
Deferred tax liabilities	-18,397	-4,549
Valuation allowance	-31	-3,984
Deferred tax asset (liability), net	-563	0
Current asset (liability), net	17,827	2,675
Noncurrent asset (liability), net	($18,390)	($2,675)

Income_Taxes_Unrecognized_Tax_

Income Taxes - Unrecognized Tax Benefits (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of the year	$377	$0	$0
Increase related to prior period tax positions	-40	-172	0
Increase related to current period tax positions	369	205	0
Balance at the end of the year	$706	$377	$0

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (Fair Value, Measurements, Recurring [Member], USD $)	Dec. 28, 2014	Dec. 29, 2013
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	$134,543	$36,033
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	3,015	18,019
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	131,528	18,014
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	3,015	18,019
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	3,015	18,019
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	131,528	18,014
Commercial Paper [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Commercial Paper [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	131,528	18,014
Commercial Paper [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$0	$0

Quarterly_Financial_Informatio2

Quarterly Financial Information (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 28, 2014	Sep. 28, 2014	Jun. 29, 2014	Mar. 30, 2014	Dec. 29, 2013	Sep. 29, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 28, 2014	Dec. 29, 2013	Dec. 30, 2012
Quarterly Financial Information Disclosure [Abstract]
Net sales	$391,349	$285,836	$285,013	$237,881	$257,033	$166,655	$145,009	$127,012	$1,200,079	$695,709	$331,240
Gross profit	101,067	78,689	80,956	63,734	68,375	44,501	43,903	36,612	324,446	193,391	90,297
Income (loss) from operations	11,669	-663	7,675	-2,951	12,922	-2,283	4,003	-1,613	15,730	13,029	-10,554
Net income (loss) before provision for income taxes	11,690	-495	7,756	-2,950	13,109	-2,251	4,001	-1,595	16,001	13,264	-10,335
PROVISION FOR INCOME TAXES	809	300	0	0	356	0	0	0	1,109	356	0
Net income (loss)	10,881	-795	7,756	-2,950	12,753	-2,251	4,001	-1,595	14,892	12,908	-10,335
Net Income (Loss) Available to Common Stockholders, Basic	10,881	-795	7,756	-2,950	4,526	-4,819	0	-4,126	14,892	0	-46,822
Net income (loss) per share attributable to Class A and Class B common stockholders--basic (in dollars per share)	$0.09	($0.01)	$0.06	($0.02)	$0.05	($0.09)	$0	($0.09)	$0.12	$0	($1.23)
Net income (loss) per share attributable to Class A and Class B common stockholders—diluted (in dollars per share)	$0.08	($0.01)	$0.06	($0.02)	$0.05	($0.09)	$0	($0.09)	$0.11	$0	($1.23)
Weighted average shares used to compute basic net income (loss) per Class A and Class B common share (in shares)	125,525,000	124,985,000	124,424,000	123,879,000	87,992,000	53,495,000	49,891,000	46,422,000	124,679,716	59,450,186	37,976,724
Weighted average shares used to compute diluted net income (loss) per Class A and Class B common share (in shares)	131,036,000	124,985,000	133,067,000	123,879,000	127,603,000	53,495,000	49,891,000	46,422,000	132,317,357	59,450,186	37,976,724
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Deferred revenue	44,243				23,250				44,243	23,250
Net sales	391,349	285,836	285,013	237,881	257,033	166,655	145,009	127,012	1,200,079	695,709	331,240
Restatement Adjustment [Member] | Out of period correction, customer merchandise credits accrual [Member]
Quarterly Financial Information Disclosure [Abstract]
Net sales		2,800
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Deferred revenue		2,800
Net sales		$2,800

Subsequent_Events_Details

Subsequent Events (Details) (Subsequent Event [Member], USD $)	0 Months Ended	3 Months Ended
In Millions, unless otherwise specified	Feb. 11, 2015	Mar. 29, 2015	Feb. 20, 2015	Jan. 23, 2015
		Segment
Restructuring Cost and Reserve [Line Items]
Number of operating segments		1
Share repurchase program, amount authorized to be repurchased	$250
Repurchase period	24 months
Minimum [Member]
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring charges expected to be incurred				1.5
Semi-annual cash bonus percentage			0.00%
Maximum [Member]
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring charges expected to be incurred				$2.50
Semi-annual cash bonus percentage			40.00%
Chief Executive Officer [Member] | Minimum [Member]
Restructuring Cost and Reserve [Line Items]
Semi-annual cash bonus percentage			0.00%
Chief Executive Officer [Member] | Maximum [Member]
Restructuring Cost and Reserve [Line Items]
Semi-annual cash bonus percentage			50.00%