NxStage Medical 10-K 16 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2017	Feb. 08, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	NXTM
Entity Registrant Name	NxStage Medical, Inc.
Entity Central Index Key	1,333,170
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		66,320,683
Entity Public Float			$ 1.6

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 64,928	$ 59,632
Accounts receivable, net	31,625	32,286
Inventory	49,212	46,845
Prepaid expenses and other current assets	7,609	6,136
Total current assets	153,374	144,899
Property and equipment, net	60,262	61,561
Field equipment, net	24,264	22,309
Deferred cost of revenues, net	31,410	33,165
Intangible assets, net	7,660	9,688
Goodwill	42,748	42,648
Other assets	5,911	2,937
Total assets	325,629	317,207
Current liabilities:
Accounts payable	14,785	14,177
Accrued expenses	27,985	30,985
Current portion of long-term debt	101	328
Other current liabilities	4,559	3,770
Total current liabilities	47,430	49,260
Deferred revenues	46,874	49,001
Long-term debt	520	1,305
Other long-term liabilities	17,824	15,568
Total liabilities	112,648	115,134
Commitments and contingencies (Note 10)
Noncontrolling interests subject to put provisions	(165)	50
Stockholders’ equity:
Undesignated preferred stock: par value $0.001 per share, 5,000,000 shares authorized; no shares issued and outstanding as of December 31, 2017 and 2016	0	0
Common stock: par value $0.001 per share, 100,000,000 shares authorized; 67,341,819 and 65,883,026 shares issued as of December 31, 2017 and 2016, respectively	67	65
Additional paid-in capital	657,640	631,219
Accumulated deficit	(421,593)	(407,601)
Accumulated other comprehensive loss	(3,673)	(6,101)
Treasury stock, at cost: 1,046,870 and 936,360 shares as of December 31, 2017 and 2016, respectively	(19,283)	(16,184)
Total NxStage Medical, Inc. stockholders’ equity	213,158	201,398
Noncontrolling interests not subject to put provisions	(12)	625
Total stockholders’ equity	213,146	202,023
Total liabilities and stockholders’ equity	$ 325,629	$ 317,207

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Undesignated preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Undesignated preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Undesignated preferred stock, shares issued (in shares)	0	0
Undesignated preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	67,341,819	65,883,026
Treasury stock, shares (in shares)	1,046,870	936,360

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Revenues	$ 393,941	$ 366,378	$ 336,123
Cost of revenues	225,653	214,393	204,652
Gross profit	168,288	151,985	131,471
Operating expenses:
Selling and marketing	68,234	63,878	58,528
Research and development	39,608	31,032	26,237
Distribution	32,484	28,579	26,211
General and administrative	41,813	32,781	35,124
Total operating expenses	182,139	156,270	146,100
Loss from operations	(13,851)	(4,285)	(14,629)
Other (expense) income:
Interest expense, net	(756)	(1,000)	(1,115)
Other (expense) income, net	(863)	(930)	561
Total other expenses	(1,619)	(1,930)	(554)
Net loss before income taxes	(15,470)	(6,215)	(15,183)
(Benefit from) provision for income taxes	(145)	1,102	1,077
Net loss	(15,325)	(7,317)	(16,260)
Less: Net loss attributable to noncontrolling interests	(1,333)	(2,546)	(918)
Net loss attributable to stockholders of NxStage Medical, Inc.	(13,992)	(4,771)	(15,342)
Add: Accretion to redemption value of noncontrolling interests	(481)	0	0
Net loss attributable to common stockholders	$ (14,473)	$ (4,771)	$ (15,342)
Net loss per share, basic and diluted (in dollars per share)	$ (0.22)	$ (0.07)	$ (0.24)
Weighted-average shares outstanding, basic and diluted (in shares)	65,856	64,520	63,384
Other comprehensive income (loss), net of tax:
Unrealized income (loss) on derivative instruments, net of income taxes	$ 1,001	$ (802)	$ (395)
Other income (loss)	1,427	(1,268)	(1,444)
Other comprehensive income (loss), net of tax:	2,428	(2,070)	(1,839)
Total comprehensive loss	(12,897)	(9,387)	(18,099)
Less: Comprehensive loss attributable to noncontrolling interests	(1,333)	(2,546)	(918)
Total comprehensive loss attributable to stockholders of NxStage Medical, Inc.	$ (11,564)	$ (6,841)	$ (17,181)

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Total NxStage Medical Inc. Stockholders' Equity	Noncontrolling Interest Not Subject to Put Provisions
Beginning balance (in shares) at Dec. 31, 2014		63,429,005
Beginning balance at Dec. 31, 2014	$ 191,555	$ 63	$ 593,073	$ (387,488)	$ (2,192)	$ (12,989)	$ 190,467	$ 1,088
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(16,260)
Net income, not subject to put provision	(16,260)			(15,342)			(15,342)	(918)
Adjustments to other comprehensive loss, net of tax	(1,839)				(1,839)		(1,839)
Shares, exercise of stock options (in shares)		1,020,552
Exercise of stock options	6,916	$ 1	7,790			(875)	6,916
Shares issued under employee restricted stock plans (in shares)		306,908
Shares issued under employee restricted stock plans	(943)		(943)				(943)
Shares issued under employee bonus plans (in shares)		66,230
Shares issued under employee bonus plans	$ 1,103		1,103				1,103
Shares issued under employee stock purchase plan (in shares)	50,343
Shares issued under employee stock purchase plan	$ 690		690				690
Stock-based compensation expense	10,774		10,774				10,774
Changes in noncontrolling interest	1,524							1,524
Ending balance (in shares) at Dec. 31, 2015		64,873,038
Ending balance at Dec. 31, 2015	193,520	$ 64	612,487	(402,830)	(4,031)	(13,864)	191,826	1,694
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(7,317)
Net income, not subject to put provision	(7,149)			(4,771)			(4,771)	(2,378)
Adjustments to other comprehensive loss, net of tax	(2,070)				(2,070)		(2,070)
Shares, exercise of stock options (in shares)		658,444
Exercise of stock options	5,914	$ 1	8,233			(2,320)	5,914
Shares issued under employee restricted stock plans (in shares)		314,013
Shares issued under employee restricted stock plans	$ (687)		(687)				(687)
Shares issued under employee stock purchase plan (in shares)	37,531
Shares issued under employee stock purchase plan	$ 767		767				767
Stock-based compensation expense	10,419		10,419				10,419
Changes in noncontrolling interest	1,309							1,309
Ending balance (in shares) at Dec. 31, 2016		65,883,026
Ending balance at Dec. 31, 2016	202,023	$ 65	631,219	(407,601)	(6,101)	(16,184)	201,398	625
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(15,325)
Net income, not subject to put provision	(15,432)			(13,992)			(13,992)	(1,440)
Adjustments to other comprehensive loss, net of tax	$ 2,428				2,428		2,428
Shares, exercise of stock options (in shares)	1,130,939	1,130,939
Exercise of stock options	$ 12,497	$ 1	15,595			(3,099)	12,497
Shares issued under employee restricted stock plans (in shares)		291,601
Shares issued under employee restricted stock plans	$ (1,349)	$ 1	(1,350)				(1,349)
Shares issued under employee stock purchase plan (in shares)	36,253	36,253
Shares issued under employee stock purchase plan	$ 855		855				855
Stock-based compensation expense	11,802		11,802				11,802
Changes in noncontrolling interest	322		(481)				(481)	803
Ending balance (in shares) at Dec. 31, 2017		67,341,819
Ending balance at Dec. 31, 2017	$ 213,146	$ 67	$ 657,640	$ (421,593)	$ (3,673)	$ (19,283)	$ 213,158	$ (12)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net loss	$ (15,325)	$ (7,317)	$ (16,260)
Adjustments to reconcile net loss to net cash flow from operating activities:
Depreciation and amortization	33,754	32,637	30,715
Stock-based compensation	11,537	10,117	12,598
Other	2,131	2,445	1,302
Changes in operating assets and liabilities:
Accounts receivable	1,056	(7,388)	(1,130)
Inventory	(22,917)	(31,069)	(12,113)
Prepaid expenses and other assets	(1,045)	(68)	(77)
Accounts payable	(22)	3,532	(2,775)
Accrued expenses and other liabilities	(1,774)	4,141	635
Deferred revenues	(2,593)	(2,443)	(2,353)
Net cash provided by operating activities	4,802	4,587	10,542
Cash flows from investing activities:
Cash paid for acquisitions, net of cash acquired	(100)	(513)	0
Purchase of cost method investment	(2,500)	0	0
Proceeds from sales of marketable securities	0	0	676
Purchases of property and equipment	(9,194)	(8,848)	(11,537)
Net cash used in investing activities	(11,794)	(9,361)	(10,861)
Cash flows from financing activities:
Issuance of shares under stock incentive plans, net of payroll taxes paid	12,003	5,994	6,663
Investment by noncontrolling interest holder	0	1,255	929
Proceeds from loans, lines of credit and capital leases	452	0	1,275
Repayments on loans and lines of credit	(164)	(384)	(143)
Repayments on capital leases	(1,306)	(1,590)	(1,391)
Net cash provided by financing activities	10,985	5,275	7,333
Foreign exchange effect on cash and cash equivalents	1,303	66	(833)
Increase in cash and cash equivalents	5,296	567	6,181
Cash and cash equivalents, beginning of year	59,632	59,065	52,884
Cash and cash equivalents, end of year	$ 64,928	$ 59,632	$ 59,065

Nature of Operations, Proposed

Nature of Operations, Proposed Merger, Basis of Presentation and Principles of Consolidation	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Nature of Operations, Proposed Merger, Basis of Presentation and Principles of Consolidation	Nature of Operations, Proposed Merger, Basis of Presentation and Principles of Consolidation Nature of Operations We are a medical technology company that develops, manufactures, markets and provides innovative products and services for patients suffering from chronic or acute kidney failure. Our primary product, the System One, was designed to satisfy an unmet clinical need for a system capable of delivering the therapeutic flexibility and clinical benefits of traditional dialysis machines in a smaller, portable, easy-to-use form that can be used by healthcare professionals and trained lay users alike in a variety of settings, including patient homes and home-like settings, including skilled nursing facilities, as well as more traditional care settings such as hospitals and dialysis centers. Given its design, the System One is particularly well-suited for home hemodialysis and a range of dialysis therapies that are more practical to deliver in the home setting, including more frequent hemodialysis and nocturnal hemodialysis. Clinical literature suggests such therapies provide patients better clinical outcomes and improved quality of life. In addition to the System One, we provide patients with our PureFlow SL accessory which prepares on-site premixed dialysate fluid in the patient's home using ordinary tap water and dialysate concentrate. We also operate a small number of NxStage Kidney Care dialysis centers, independently and in some instances as joint ventures, that treat end-stage renal disease (ESRD) patients directly. These centers have provided us with valuable experience to better meet and anticipate the needs of both our customers and patients, while optimizing our product technology. In addition, these centers have provided us with the opportunity to innovate and foster new care delivery models to advance the standard of renal care across other markets. More specifically, at NxStage Kidney Care we offer a range of treatment options, including home hemodialysis, peritoneal dialysis and flexible in-center hemodialysis. We are headquartered in Lawrence, Massachusetts, with manufacturing facilities in Mexico, Germany and Italy. Through our international network of affiliates and distribution partners, patients in 21 countries have been treated with our products. Proposed Merger On August 7, 2017, we entered into the Merger Agreement with Fresenius, pursuant to which we will merge with a wholly-owned subsidiary of Fresenius, subject to certain conditions. At the closing of the Merger, all outstanding shares of our common stock (except those held by us, Fresenius or its wholly-owned subsidiaries or any stockholders properly exercising their appraisal rights under the General Corporation Law of the State of Delaware) would be converted into the right to receive $30.00 per share in cash, subject to any applicable tax withholdings. The closing of the Merger is conditioned, among other things, on receipt of regulatory approval from the FTC and the expiration of applicable waiting periods, or extensions thereof, under the HSR Act. Pursuant to the HSR Act, we and Fresenius each submitted pre-merger notification filings to the FTC and Department of Justice, Antitrust Division. On October 18, 2017, we and Fresenius each received a Request for Additional Information and Documentary Material (also known as a Second Request) from the FTC. The effect of the Second Request is to extend the waiting period imposed by the HSR Act until 30 days after Fresenius and we have substantially complied with the Second Request, unless that period is terminated sooner by the FTC. By agreement with the FTC, the parties may voluntarily extend the time for closing beyond the expiration of the HSR Act waiting period. The parties continue to work to obtain FTC approval of the proposed transaction. On October 27, 2017, the stockholders of NxStage Medical, Inc. voted to approve the Merger Agreement. In addition, the Merger has cleared antitrust review in Germany and the UK. See “Risk Factors” in Part I Item 1A of this Annual Report for additional information. The Merger Agreement may be terminated by us or Fresenius if the Merger is not closed by August 7, 2018 (the End Date), although Fresenius may extend the End Date for up to 180 days under certain circumstances in order to obtain required antitrust clearances. The Merger Agreement generally requires each party to use its reasonable best efforts to obtain all consents and clearances required under any antitrust law, except that Fresenius is not required (i) to litigate against a governmental entity or (ii) to divest or to take any other actions with respect to any assets or business of Fresenius, its subsidiaries or the Company, other than, if necessary to obtain antitrust clearances, with respect to certain Company assets. Fresenius is required to pay us a termination fee of $100 million (the Reverse Termination Fee) if the Merger Agreement is terminated by us or Fresenius (i) if the End Date and any applicable extension has passed or (ii) if a court or other governmental entity issues a final, nonappealable order or takes any other actions that permanently prohibits the Merger or makes closing the Merger illegal (in each case because approval under applicable antitrust laws remains the only unsatisfied closing condition). We would be required to pay Fresenius a termination fee of $60 million (the Termination Fee) if all of the following conditions were applicable: (i) the Merger Agreement is terminated because the End Date has passed or we have breached a representation or warranty, (ii) an alternative acquisition proposal has been publicly made and not publicly withdrawn at least ten days prior to the termination, and (iii) within 12 months following such termination, we enter into an alternative acquisition agreement or an alternative acquisition is consummated. Nonetheless, we will not be required to pay the Termination Fee if the Merger Agreement is terminated due to failure to obtain required antitrust approvals by the End Date and Fresenius is required to pay the Reverse Termination Fee. The Merger Agreement includes customary representations, warranties and covenants. Pursuant to the Merger Agreement, we agreed to use commercially reasonable efforts to operate our business in all material respects in the ordinary course until closing. Basis of Presentation The accompanying consolidated financial statements of NxStage Medical, Inc. have been prepared in accordance with accounting principles generally accepted in the United States of America (U.S. GAAP) and with the requirements of Regulation S-X. The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and 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. Actual results could differ from those estimates. Such financial statements reflect all adjustments that, in the opinion of management, are necessary for a fair presentation of the results of the periods presented. All such adjustments are of a normal recurring nature. Principles of Consolidation Our consolidated financial statements include the accounts of NxStage Medical, Inc. and our wholly-owned subsidiaries and other entities in which we maintain a majority voting interests or for which we maintain effective control including variable interest entities (VIEs) for which we are deemed the primary beneficiary. All significant intercompany balances and transactions have been eliminated. Noncontrolling interests represent the proportionate equity interests in the consolidated entities that are not wholly owned by us. Noncontrolling interests of acquired entities are recognized at their initial fair value.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Revenue Recognition We recognize revenue from product sales and services when earned. Revenues are recognized when: (a) there is persuasive evidence of an arrangement, (b) the product has been shipped or services and supplies have been provided to the customer, (c) the sales price is fixed or determinable and (d) collection is reasonably assured. Certain agreements with distributors allow for product returns and credits. For shipment of product sold to distributors, revenue is recognized at the time of sale if a reasonable estimate of future returns or credit can be made. If a reasonable estimate of future returns or credit cannot be made, we recognize revenue using the "sell-through" method. Under the "sell-through" method, revenue and related costs of revenue is deferred until the final resale of such products to end customers. In addition to contractually determined volume discounts, in many agreements we offer rebates based on sales to specific end customers and discounts for early payment. Rebates and discounts are recorded as a reduction of sales and trade accounts receivable, based on our best estimate of the amount of probable future rebate or discount on current sales. We enter into multiple-element arrangements that may include a combination of equipment, related disposables and services. Revenue arrangements with multiple elements are divided into separate units of accounting if specified criteria are met, including whether the delivered element has stand-alone value to the customer, the consideration received is allocated among the separate units based on their respective selling price, and the applicable revenue recognition criteria are applied to each of the separate units. We determine selling price using vendor specific objective evidence (VSOE), if it exists, otherwise third-party evidence of selling price is used. If neither VSOE nor third-party evidence of selling price exists for a unit of accounting, we use best estimated selling price (BESP). We generally expect that we will not be able to establish third-party evidence due to the nature of our products and the markets in which we compete, and, as such, we typically will determine selling price using VSOE or BESP. We determine BESP for an individual element based on consideration of both industry and Company-specific factors, including the selling price and profit margin for similar products, the cost to produce the deliverable and the anticipated margin on that deliverable and the characteristics of the varying markets in which the deliverable is sold. Any tax assessed by a governmental authority that is incurred as a result of a revenue transactions (e.g. sales tax) is excluded from revenues and reported on a net basis System One Segment We derive revenue in the home market from sales of the System One equipment and/or PureFlow SL hardware and sales of disposable products. For the System One equipment and PureFlow SL hardware sales transactions, sold to dialysis clinic customers in the home market, due to the depot service model whereby equipment requiring service is picked up and a replacement device is shipped to the site of care, we recognize upfront fees received from equipment sales transactions as revenue on a straight-line basis over the expected term of our remaining service obligation and direct costs relating to the delivered equipment are classified in deferred cost of revenues and amortized over the same expected period as the related revenue. Disposable products revenue is recognized on a monthly basis. We also offer a month-to-month System One equipment and PureFlow SL hardware rental arrangements. Under these arrangements, revenue is recognized on a monthly basis in accordance with agreed upon contract terms and pursuant to binding customer purchase orders and fixed payment terms. Our sales arrangements with our international distributors are structured as direct product sales and have no significant post-delivery obligations with the exception of standard warranty obligations. Revenue from direct product sales is recognized upon delivery in accordance with contract terms. In the critical care market, we structure sales of the System One and disposable products as direct product sales and have no significant post-delivery obligations with the exception of standard warranty obligations. Revenue from direct product sales is recognized upon delivery in accordance with contract terms. Certain of these arrangements provide for training, technical support and extended warranty services to our customers. We recognize training and technical support revenue when the related services are performed. In the case of extended warranty, the service revenue is recognized ratably over the extended warranty period. In-Center Segment Our In-Center segment sales are structured as direct product sales primarily through distributors, and we have no significant post delivery obligations with the exception of standard warranty obligations. Revenue from direct product sales is recognized upon delivery in accordance with contract terms. Services Segment Revenues in our Services segment are derived from dialysis care services provided to patients at our NxStage Kidney Care dialysis centers. Revenues are recognized based on a customary fee schedule, net of estimated contractual allowances to reflect the estimated amounts to be received from the payor. Revenues are recognized in the period in which services are provided when we have the ability to reasonably estimate amounts ultimately collectible from the payor. In instances where we do not have the ability to reasonably estimate amounts ultimately collectible, as is often the case with non-contracted commercial health plans and amounts due from patients (including co-pay and deductible amounts), revenue is recognized in the period in which cash is received. Foreign Currency Translation and Transactions Assets and liabilities of our foreign operations are translated into U.S. dollars at current exchange rates, and income and expense items are translated at average rates of exchange prevailing during the year. Foreign exchange gains and (losses) on intercompany loans considered permanent investments are recorded in other comprehensive loss. Gains and (losses) realized from transactions denominated in foreign currencies, including intercompany balances not considered permanent investments, are included in the consolidated statements of comprehensive loss within other income (expense), net. Cash and Cash Equivalents We consider all highly-liquid investments purchased with original maturities of 90 days or less to be cash equivalents. Cash equivalents include amounts invested in treasury obligation money market funds. Cash equivalents are stated at cost plus accrued interest, which approximates fair value. Concentration of Credit Risk Financial instruments that potentially subject us to concentrations of credit risk consist principally of cash and cash equivalents, derivatives and accounts receivable. To mitigate such risk, with respect to cash and cash equivalents, we place our cash in bank deposit accounts with financial institutions that have investment grade ratings and capital ratios exceeding minimum Federal Reserve Adequacy Guidelines and in treasury obligation money market funds. To mitigate concentration of credit risk with respect to derivatives we enter into transactions with highly-rated financial institutions and frequently monitor the credit worthiness of our counterparties. Concentration of credit risk with respect to accounts receivable is primarily limited to certain customers to whom we make substantial sales. No customer represented more than 10% of accounts receivable at December 31, 2017 and two customers represented 12% and 10% of accounts receivable at December 31, 2016 . To reduce risk, we routinely assess the financial strength of our customers and closely monitor their amounts due and, as a result of our assessment, we believe that our accounts receivable credit risk exposure is limited. Historically, we have not experienced any significant credit losses related to an individual customer or group of customers in any particular market or geographic area. We maintain an allowance for doubtful accounts based on an analysis of historical losses from uncollectible accounts, aging of unpaid accounts receivable balances and risks identified for specific customers who may not be able to make required payments. Provisions for the allowance for doubtful accounts are recorded in general and administrative expenses in the accompanying consolidated statements of comprehensive loss. Activity related to allowance for doubtful accounts consisted of the following (in thousands): Year Ended Balance at Beginning of Year Provision Write-offs Balance at End of Year December 31, 2017 $ 535 $ 471 $ (191 ) $ 815 December 31, 2016 $ 417 $ 179 $ (61 ) $ 535 December 31, 2015 $ 425 $ 20 $ (28 ) $ 417 We use and are dependent upon a number of single source suppliers of raw materials, components, finished goods and sterilization services. We are dependent on the ability of our suppliers to provide products on a timely basis and on favorable pricing terms. The loss of certain principal suppliers or a significant reduction in product availability from principal suppliers would have a material adverse effect on us, at least in the near term. We believe that our relationships with our suppliers are satisfactory. Fair Value Measurements U.S. GAAP defines fair value 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. U.S. GAAP requires an entity to maximize the use of observable inputs, where available, and minimize the use of unobservable inputs when measuring fair value. The Company has certain financial assets and liabilities that are measured at fair value on a recurring basis, certain nonfinancial assets that may be measured at fair value on a nonrecurring basis. The fair value disclosures of these assets and liabilities are based on a three-level hierarchy, which is defined as follows: Level 1 Quoted prices in active markets for identical assets or liabilities that the entity can access at the measurement date. Level 2 Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. Our assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment and considers factors specific to the asset or liability. Derivative Instruments and Hedging Derivative instruments, namely our foreign exchange forward contracts, are recognized on the balance sheet at fair value at the balance sheet date. Changes in the fair value of derivatives that are designated and highly effective as cash flow hedges are deferred in accumulated other comprehensive income (loss) and subsequently recognized in cost of revenues in the same period the hedged items are recognized. The ineffective portion of derivative instruments designated as cash flow hedges are recorded in other income (expense), net. If the underlying forecasted transaction does not occur, or it becomes probable that it will not occur, the gains and losses on the related derivative instrument are recognized in earnings and any related gains and losses recorded in other comprehensive income (loss) are reclassified into earnings. Inventory Inventory is stated at the lower of cost, determined using the first-in first-out method (FIFO), or market (net realizable value). We write down the carrying value of inventory for estimated obsolescence when warranted by an amount equal to the difference between the cost of inventory and the estimated market value based on assumptions of future demand and remaining shelf-life. We also review our inventory value to determine if it reflects the lower of cost or market based on factors such as inventory items sold at negative gross margins and purchase commitments. Property and Equipment and Field Equipment Property and equipment and field equipment are recorded at cost less accumulated depreciation. Depreciation is provided over the estimated useful lives of the related assets using the straight-line method for financial statement purposes. The estimated useful lives of our assets are periodically reviewed for reasonableness. Changes in useful lives are accounted for prospectively. Repairs and maintenance are expensed as incurred. When property and equipment are retired, sold or otherwise disposed of, the asset's carrying amount and related accumulated depreciation are removed from the accounts and any gain or loss is included in operations. When field equipment is sold, the asset's carrying amount and related accumulated depreciation is removed from the accounts and any gain or loss is deferred and recognized in operations on a straight-line basis over the same period as the related revenues. We capitalize certain costs, including internal payroll and external direct project costs, incurred in connection with developing or obtaining software designated for internal use. These costs are included in property and equipment and are amortized over the estimated useful lives of the related software. Construction-in-process is stated at cost, which includes the cost of construction and other direct costs attributable to the construction. No provision for depreciation is made on construction-in-process until such time as the relevant assets are completed and put into use. Construction-in-process at December 31, 2017 and 2016 primarily represents the costs of building, machinery and equipment under installation. Field equipment consists of equipment being utilized under disposable-based rental agreements as well as “service pool” equipment. Service pool equipment is equipment owned and maintained by us that are swapped for equipment that need repairs or maintenance by us while being rented or owned by a customer. We record a provision for any excess, lost or damaged equipment when warranted based on an assessment of the equipment in the service pool. Write-downs for equipment are included in distribution expenses. The estimated useful lives of property and equipment and field equipment are as follows: Estimated Useful Life Buildings 30 years Equipment and tooling 5 to 12 years Leasehold improvements Lesser of the lease term (including any renewal periods if appropriate) or estimated useful life of the asset Computer and office equipment 3 to 5 years Molds 5 to 7 years Furniture 5 to 7 years Field equipment 5 to 7 years Intangibles and Other Long-Lived Assets Intangible assets are carried at cost less accumulated amortization. For assets with determinable useful lives, amortization is recognized using the straight-line method over the estimated economic lives of the respective intangible assets. Long-lived assets, including intangible assets, are evaluated for recoverability whenever events or circumstances indicate that their carrying value may not be recoverable. Recoverability of long-lived assets is assessed at the lowest level for which discrete cash flows are available and is measured by comparing the asset group’s carrying value to its expected non-discounted future cash flows. If the sum of the expected non-discounted future cash flows is less than the carrying amount of the long-lived assets, an impairment loss is recognized for excess of the carrying amount of the asset group over its fair value. In 2017 , 2016 and 2015 , events and circumstances have indicated that certain long-lived tangible assets in the Services segment may not be recoverable. Therefore, a recoverability test was performed at the center level by comparing the carrying value of each center to its estimated future undiscounted cash flows, within the initial lease term (which is the equivalent to the depreciable life of the centers' most significant asset, its leasehold improvements). As of December 31, 2017 , our expected non-discounted future cash flows for the majority of our centers indicated such carrying amounts were expected to be recovered. We recorded an impairment charge of $ 0.3 million , $ 0.5 million and $ 0.2 million in 2017 , 2016 and 2015 , respectively, in cost of revenues to write-down certain center level assets within our Services segment. Our expected non-discounted future cash flows used in our impairment testing are based upon cash flow projections and, if appropriate, include assumed proceeds upon sale of the asset group at the end of the cash flow period. We believe our procedures for developing cash flow projections, including the estimated sales proceeds, are reasonable and consistent with current market conditions for each of the dates when impairment testing has been performed. Developing cash flow projections requires significant estimates and judgment. Among other things, slower than expected patient ramp or lower than expected reimbursement rates would negatively impact our cash flow projections in the near term. Fair value of the asset group was estimated using a discounted cash flow approach. Estimating fair value requires significant judgment in the selection of the valuation technique and assumptions used in developing cash flow projections, growth rates and discount rates. Our assumptions are based on our best estimates, using appropriate and customary market participant assumptions. Any adverse changes in certain valuation assumptions could result in the need to record additional impairment to write down all or a portion the centers’ remaining asset carrying value. Additionally, as discussed below in Note 2, effective January 1, 2018, we will adopt the new revenue recognition guidance under ASC 606 . In connection with the adoption of ASC 606, we anticipate recording an increase to center net assets within our Services segment. If the increase in center net assets is greater than the excess fair value over the carrying value of net assets an impairment charge would be recognized. We had $13.9 million of long-lived assets at our Services segment at December 31, 2017 . It is reasonably possible that our cash flow projections may change or the carrying value of our net assets many change in the near term resulting in the need to record an impairment charge for at least some portion of these assets. Assets to be disposed of are reported at the lower of the carrying amount or fair value less selling costs. Goodwill Goodwill represents the excess of the cost of an acquired business over the acquisition value of the related net assets at the date of acquisition. We test goodwill at least annually for impairment during the fourth quarter, or more frequently when events or changes in circumstances indicate that the goodwill might be impaired. This test includes first a qualitative assessment and then, if necessary, a quantitative assessment to determine if the fair value of a reporting unit is less than its carrying amount. Our System One, In-center and Services reporting units contain goodwill of $41.1 million, $0.5 million and $1.1 million, respectively. Factors considered in the qualitative assessment include, but are not limited to, both macroeconomic conditions and entity-specific conditions. For the quantitative assessment, the reporting unit's fair value is estimated using a discounted cash flow or other fair value measurement. During 2017 , 2016 and 2015 we utilized the qualitative assessment to assess the fair value of our System One and In-center reporting units and concluded that it was more likely than not that the fair value of our reporting units was greater than their carrying value. During 2017 , for our Services reporting unit, we utilized the quantitative assessment noting that the fair value of the reporting unit exceeds its carrying value, indicating that goodwill was not impaired. We estimated the fair value of our Services reporting unit using a discounted cash flow approach. Estimating the fair value of our Services reporting unit requires significant judgment in the selection of the valuation technique and assumptions used in cash flow projections, growth rates and discount rates. Our assumptions are based on our best estimates, using appropriate and customary market participant assumptions. Additionally, as discussed in Note 2 below, effective January 1, 2018, we adopted the new revenue recognition guidance under ASC 606 that we anticipate will result in an increase to our Services center reporting units net asset value. If the increase in net assets is greater than the excess fair value over the carrying value of net assets, an impairment charge would be recognized. Developing cash flow projections involves significant judgment with respect to patient ramp and reimbursement rates, operating income, capital expenditures and changes in working capital. Reductions in our cash flow projections due to slower than expected patient ramp or lower than expected reimbursement rates, among other things, or adverse changes in certain valuation assumptions or changes in the reporting units net assets resulting from the adoption of ASC 606 could result in a goodwill impairment charge of up to $ 1.1 million in the future. Stock-Based Compensation Stock-based compensation expense is estimated as of the grant date based on the fair value of the award. We use the Black-Scholes option pricing model to estimate the fair value of stock options and quoted market prices of our common stock to estimate fair value of restricted stock. The expected term is estimated based on the contractual term of each grant and takes into account the historical experience and relevant factors concerning expected exercise and termination behavior of participants. The risk free interest rate for each grant is equal to the U.S. Treasury rate in effect at the time of grant for instruments with an expected life similar to the expected term. The stock volatility assumption is based solely on our historical volatility over the expected term of the award. The dividend yield of zero is based upon the fact that we have not historically granted cash dividends, and do not expect to issue dividends in the foreseeable future. We recognize stock-based compensation expense over the requisite service period, which equals the vesting period, net of forfeitures. Forfeiture rates are estimated based on historical pre-vesting forfeiture history and are updated on a quarterly basis to reflect actual forfeitures of unvested awards and other known events. For awards that vest based on employment, we recognize the associated compensation expense on a straight-line basis. For performance based awards, we recognize expense using the graded vesting methodology based on the number of shares expected to vest. Compensation expense associated with these performance based awards is adjusted quarterly to reflect subsequent changes in the estimated outcome of performance-related conditions until the date the results are determined. Warranty Costs We accrue estimated costs that we may incur under our product warranty programs at the time the product revenue is recognized, based on contractual rights and historical experience. Warranty expense is included in cost of revenues in the consolidated statements of comprehensive loss. The following is a rollforward of our warranty accrual (in thousands): Year Ended Balance at Beginning of Year Provision Usage Balance at End of Year December 31, 2017 $ 280 $ 445 $ (432 ) $ 293 December 31, 2016 $ 389 $ 457 $ (566 ) $ 280 December 31, 2015 $ 287 $ 526 $ (424 ) $ 389 Distribution Expenses Distribution expenses are charged to operations as incurred and consist of costs incurred in shipping product to and from customers and the cost of any equipment lost or damaged in the distribution process. Shipping and handling costs billed to customers are included in revenues. Research and Development Costs Research and development costs are charged to operations as incurred. Income Taxes We record the tax effect of transactions when such transactions are recorded in our consolidated statement of comprehensive loss. We record a deferred tax asset or liability based on the difference between the financial statement and tax basis of assets and liabilities, as measured by the enacted tax rates. Our provision for income taxes represents the amount of taxes currently payable, if any, plus the change in the amount of net deferred tax assets or liabilities. A valuation allowance is provided against net deferred tax assets if recoverability is uncertain on a more likely than not basis. We periodically assess our exposures related to our provisions for income taxes and accrue for contingencies that may result in potential tax obligations. For those positions where it is more likely than not that a tax benefit will be sustained, we record the largest amount of tax benefit with a greater than 50 percent likelihood of being realized upon ultimate settlement with a taxing authority that has full knowledge of all relevant information. For those income tax positions where it is not more likely than not that a tax benefit will be sustained, no tax benefit is recognized in the financial statements. We recognize interest and penalties for uncertain tax positions in income tax expense. We conduct business globally and file income tax returns in the U.S. federal jurisdiction, various states and foreign jurisdictions. We estimate our income taxes in each of the jurisdictions in which we operate. We have accumulated significant losses since our inception in 1998. The utilization of these losses may be limited in future years based on the profitability of certain entities. Subsequent Events Events occurring subsequent to December 31, 2017 have been evaluated for potential recognition or disclosure in the consolidated financial statements. Recent Accounting Pronouncements Recently Implemented Accounting Pronouncements In July 2015, the Financial Accounting Standards Board (FASB) issued ASU No. 2015-11, Inventory (Topic 330): "Simplifying the Measurement of Inventory." The update requires that an entity should measure in scope inventory at the lower of cost and net realizable value. Net realizable value is the estimated selling prices in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation. The amendments were effective for us beginning January 1, 2017. The adoption of this update did not have a material impact on our financial statements. In March 2016, the FASB issued ASU No. 2016-09: “Improvements to Employee Share-Based Payment Accounting,” which simplifies several aspects of the accounting for employee share-based payment transactions for both public and nonpublic entities, including the accounting for income taxes, forfeitures, and statutory tax withholding requirements, as well as classification in the statement of cash flows. The new guidance was effective for us beginning January 1, 2017. We have elected to continue to estimate forfeiture rates. This new standard impacts our income tax footnote disclosures. We have tax effected federal net operating losses of $18.0 million and state net operating losses of $1.6 million that are attributable to excess tax deductions related to stock-based compensation from prior years. Upon adoption, the cumulative excess tax deductions related to stock-based compensation that were previously unrecognized are being recognized as a deferred tax asset and are fully offset by a valuation allowance. Other than this change in our income tax footnote disclosures, the adoption does not have a material impact on our financial statements. In January 2017, the FASB issued ASU No. 2017-04: "Intangibles - Goodwill and Other Topics (Topic 350): Simplifying the Test for Goodwill Impairment". The purpose of this update is to reduce the cost and complexity of evaluating goodwill for impairment. It eliminates the need for entities to calculate the impaired fair value of goodwill by assigning the fair value of a reporting unit to all of its assets and liabilities as if that reporting unit had been acquired in a business combination. Under this update, an entity will perform its goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An impairment charge is recognized for the amount by which the carrying value exceeds the reporting unit's fair value. We elected to early adopt this update on a prospective basis for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The adoption of this update did not have a material impact on our financial statements. In May 2017, the FASB issued ASU No. 2017-09: "Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting". The purpose of this update is to reduce the diversity in practice and result in fewer changes to the terms of an award being accounted for as modifications. It will allow companies to make non-substantive changes to their share-based payment awards, without accounting for them as modifications. It does not change the accounting for modifications. Under this update, an entity will apply the modification accounting guidance only if the value (or calculated value or intrinsic value, if those measurement methods are used), vesting conditions or classification of the award as an equity or liability instrument changes. This update also clarifies that a modification to an award could be significant and therefore require disclosure, even if modification accounting is not required. The new guidance will be applied prospectively to awards modified on or after the adoption date. We elected to early adopt this update in the second quarter of 2017. The adoption of this update did not have a material impact on our financial statements. Recent Accounting Pronouncements Not Yet Adopted In May 201 4, the FASB issued ASU No. 2014-9: “Revenue from Contracts with Customers” (ASC 606). The standard provides that revenue should be recognized when an entity transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In addition, the standard requires disclosure of the nature, amount, timing and uncertainty of revenues and cash flow arising from contracts with customers. The FASB has issued several amendments and updates to the new revenue standard, including how an entity should identify performance obligations. As amended, the new guidance is effective for us beginning January 1, 2018. We have elected to adopt ASC 606 using the modified retrospective method approach as of January 1, 2018. This approach was applied to all contracts not completed as of January 1, 2018. The adoption of ASC 606 is expected to have a material effect on our consolidated financial statements primarily relating to the timing of revenue recognition for our Services segment along with enhanced footnote disclosures related to customer contracts. We are working to complete our evaluation of the impact of the standard on significant contracts from each of our business segments. We are evaluating the impact the standard will have on our disclosures along with any related indirect effects of adoption and are implementing changes to our current policies and practices, accounting systems and internal controls over financial reporting to address the requirements of the standard. The qualitative assessment of the standard provided below are estimates of the expected effects of the adoption of ASC 606. This represents our best estimate of the effects of adopting ASC 606 at the time of the preparation of this Annual Report on Form 10-K. The actual impact of ASC 606 is subject to change from these estimates and such change may be significant, pending the completion of our assessment in the first quarter of 2018. System One Segment Revenue . We expect that the deliverables under the current guidance will be consistent with performance obligations identified under ASC 606. Unde

Inventory

Inventory	12 Months Ended
	Dec. 31, 2017
Inventory Disclosure [Abstract]
Inventory	Inventory Inventory includes material, labor and overhead. The components of inventory are as follows (in thousands): December 31, 2017 2016 Purchased components $ 14,947 $ 14,967 Work in process 13,433 13,939 Finished goods 20,832 17,939 $ 49,212 $ 46,845

Property and Equipment, Field E

Property and Equipment, Field Equipment and Deferred Cost of Revenues	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property and Equipment, Field Equipment and Deferred Cost of Revenues	Property and Equipment, Field Equipment and Deferred Cost of Revenues Property and Equipment, net The components of property and equipment, net are as follows (in thousands): December 31, 2017 2016 Equipment and tooling $ 44,823 $ 39,921 Leasehold improvements 34,812 35,146 Computer and office equipment 8,593 10,035 Molds 7,573 6,805 Furniture 3,612 3,561 Building 9,414 8,057 Land 1,091 956 Construction-in-process 7,138 4,237 117,056 108,718 Less accumulated depreciation (56,794 ) (47,157 ) Property and equipment, net $ 60,262 $ 61,561 Depreciation expense, including amortization of capital leases, for property and equipment was $12.2 million , $11.6 million and $10.4 million during 2017 , 2016 and 2015 , respectively. Capitalized computer development costs, net were $ 0.9 million and $1.8 million at December 31, 2017 and December 31, 2016 respectively, and we recognized amortization expense of $ 0.9 million during each of 2017 , 2016 and 2015 . Our property and equipment includes the following amounts for assets subject to capital leases (amounts in thousands): December 31, 2017 2016 Manufacturing facility in Germany $ 24,135 $ 21,007 Other assets subject to capital lease 4,453 3,024 Less accumulated depreciation (8,979 ) (6,402 ) Assets subject to capital leases, net $ 19,609 $ 17,629 Manufacturing Facility in Germany Pursuant to our Dialyzer Production Agreement entered into in May 2009 with Asahi we agreed to oversee construction of a new manufacturing facility in Germany which was completed in December 2012 and operate the facility and manufacture dialyzers for our own use and for sale to Asahi under a manufacturing agreement during the initial term of the agreement through June 2021 and thereafter, unless either party provides notice of its intent not to renew. Asahi funded construction costs of the facility, including land, building and equipment. Given our involvement in the facility during construction and our continued involvement in its operation we have recorded the cost of the new facility, including building and equipment, within property and equipment, net on our consolidated balance sheet, as required, along with a corresponding liability which has been divided into two separate components, namely a capital lease obligation and deferred revenue, based on their relative fair values. The capital lease obligation is decreased by payments made to Asahi for dialyzers manufactured for our own use and increased by interest expense. The deferred revenue is recognized in revenues on a straight-line basis over the expected term of the Dialyzer Production Agreement. The fair value of the capital lease obligation was determined based on the present value of the financing payments due plus the residual value guarantee. The key assumptions used to determine the fair value of this liability included our incremental borrowing rate, the fixed amount per dialyzer payment due to Asahi totaling fifty percent of the cost of the facility paid by Asahi, and the estimated residual value of the facility assets at the end of the estimated lease term all of which we determined to be Level 3 inputs within the fair value hierarchy. The fair value of the deferred revenue was determined using cost plus a reasonable margin for contract manufacturing in Germany, which we determined to be Level 3 inputs within the fair value hierarchy. The capital lease obligation and deferred revenue balances are $12.0 million and $6.4 million , respectively, at December 31, 2017 . Field Equipment, net The components of field equipment, net are as follows (in thousands): December 31, 2017 2016 Field equipment $ 75,823 $ 70,743 Less accumulated depreciation (51,559 ) (48,434 ) Field equipment, net $ 24,264 $ 22,309 Depreciation expense for field equipment, which is recorded in costs of revenues in the consolidated statements of comprehensive loss, was $6.2 million , $5.5 million and $5.0 million during 2017 , 2016 and 2015 , respectively. Deferred Costs of Revenues, net The components of deferred costs of revenues, net are as follows (in thousands): December 31, 2017 2016 Deferred costs of revenues $ 137,734 $ 126,375 Less accumulated amortization (106,324 ) (93,210 ) Deferred costs of revenues, net $ 31,410 $ 33,165 Amortization expense of direct costs relating to deferred equipment revenues was $13.1 million , $13.3 million and $12.6 million during 2017 , 2016 and 2015 , respectively.

Intangible Assets

Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	Intangible Assets The components of intangible assets, net are as follows (in thousands): December 31, 2017 December 31, 2016 Estimated Cost Accumulated Amortization Cost Accumulated Amortization Useful Life Bloodline, needle and other patented and unpatented technology $ 6,200 $ (6,200 ) $ 6,200 $ (6,200 ) 8 years Trade names 2,300 (1,684 ) 2,300 (1,520 ) 14 years Customer relationships 26,151 (19,107 ) 26,138 (17,230 ) 10/14 years Intangible assets, net $ 34,651 $ (26,991 ) $ 34,638 $ (24,950 ) We recognized amortization expense of $2.0 million , $2.0 million and $2.6 million during 2017 , 2016 and 2015 , respectively. The estimated future aggregated amortization expense for intangible assets as of December 31, 2017 is as follows (in thousands): 2018 $ 2,036 2019 2,036 2020 2,036 2021 1,552 $ 7,660

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Net Loss per Share	Net Loss per Share Basic net loss per share is computed by dividing loss attributable to NxStage Medical, Inc. common stockholders (the numerator) by the weighted-average number of common shares outstanding (the denominator) for the period. The computation of diluted loss per share is similar to basic loss per share, except that the denominator is increased to include the number of additional common shares that would have been outstanding if the potentially dilutive common shares had been issued. The following potential common stock equivalents, as calculated using the treasury stock method, were not included in the computation of diluted net loss per share as their effect would have been anti-dilutive due to the net loss incurred (in thousands): Years Ended December 31, 2017 2016 2015 Options to purchase common stock 1,100 785 732 Unvested restricted stock 224 361 350 Total 1,324 1,146 1,082

Accrued Expenses, Other Current

Accrued Expenses, Other Current Liabilities, and Other Long Term Liabilities	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued Expenses, Other Current Liabilities, and Other Long Term Liabilities	Accrued Expenses, Other Current Liabilities, and Other Long Term Liabilities The components of accrued expenses are as follows (in thousands): December 31, 2017 2016 Payroll, compensation and related benefits $ 13,195 $ 14,086 Distribution expenses 4,914 4,804 General and administrative expenses 1,670 4,415 Other 8,206 7,680 Total $ 27,985 $ 30,985 The components of other current liabilities are as follows (in thousands): December 31, 2017 2016 Capital lease obligations $ 2,131 $ 1,840 Deferred revenue, current portion 1,473 1,035 Other 955 895 Total $ 4,559 $ 3,770 The components of other long term liabilities are as follows (in thousands): December 31, 2017 2016 Capital lease obligations $ 11,589 $ 9,991 Lease incentive obligations 2,652 3,059 Benefit plan obligations 2,060 1,678 Other 1,523 840 Total $ 17,824 $ 15,568

Debt and Capital Lease Obligati

Debt and Capital Lease Obligations	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Debt and Capital Lease Obligations	Debt and Capital Lease Obligations Revolving Line of Credit We have a revolving line of credit, currently with Capital One Financial Corporation and SVB, that allows for borrowings up to $35 million . Availability of credit is subject to a borrowing base that is calculated with reference to certain of our accounts receivable, inventory and equipment, and adjustments to such borrowing base are at the discretion of the lenders. The revolving line of credit is secured by substantially all of our assets and expires in June 2019 . Borrowings bear interest at an annual rate equal to (1) a LIBOR rate plus 2.5% or (2) a base rate plus 1.5% , where the base rate is the highest of (a) the Prime Rate, (b) the Federal Funds Rate plus 0.5% and (c) a LIBOR rate plus 1% , at our election. The revolving credit facility requires us to comply with certain covenants while borrowings are outstanding and contains events of default customary for a transaction of this type. Other Debt We have several smaller loans with original principal amounts totaling $1.1 million with annual interest rates of approximately 2.0% to 6.0% , payable over a period of five to ten years secured by certain assets. In May 2017, we extinguished a loan with a balance of $0.9 million and simultaneously entered into a capital lease of certain property and equipment for the same amount. The capital lease obligation is payable over five years. This debt extinguishment and capital lease financing represent a noncash investing and financing activity. Capital Lease Obligations Our capital lease obligations consist of certain property and equipment financed through capital leases and our capital lease obligation due to Asahi related to the manufacturing facility in Germany. Approximate future minimum payments under our capital leases as of December 31, 2017 are as follows (in thousands): 2018 $ 1,674 2019 1,733 2020 1,792 2021 1,932 2022 1,820 Thereafter (1) 7,539 Total minimum lease payments 16,490 Less: Amount representing interest (2,770 ) Present value of future minimum lease payments $ 13,720 _________________________________ (1) Amount includes $6.9 million representing the estimated residual value of the manufacturing facility in Germany at the end of the estimated lease term, which only becomes due and payable at Asahi's option if we terminate our agreement with Asahi.

Business Segment and Geographic

Business Segment and Geographic Information	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Business Segment and Geographic Information	Business Segment and Geographic Information We have three reportable business segments: System One, In-Center, and Services. The operating results of NxStage Kidney Care are included in our Services segment. We refer to our System One segment, In-Center segment, and Other category as our products business. Our System One segment includes revenues from the sale and rental of the System One and PureFlow SL dialysate preparation equipment and the sale of disposable products to customers in the home market, including through our NxStage Kidney Care dialysis centers, and critical care market. The home market is devoted to the treatment of ESRD patients in the home or a home-like setting, including skilled nursing facilities, while the critical care market is devoted to the treatment of hospital-based patients with acute kidney failure or fluid overload. Some of our largest customers in the home market provide outsourced renal dialysis services to some of our customers in the critical care market. Sales of product to both markets are made primarily through dedicated sales forces and distributed directly to the customer, or the patient, with certain products sold through distributors. Our In-Center segment includes revenues from the sale of blood tubing sets and needles for hemodialysis primarily for the treatment of ESRD patients at dialysis centers and needles for apheresis. Nearly all In-Center products are sold through national distributors. The remainder of our products business, which is included within the Other category, relates to the manufacturing of dialyzers for sale to Asahi and research and development and general and administrative expenses that are excluded from the segment operating performance measures. Our Services segment includes revenues from dialysis services provided to patients at our NxStage Kidney Care dialysis centers. Sales of the System One and related products to our NxStage Kidney Care dialysis centers are included in System One segment revenues, which are then eliminated upon consolidation. The accounting policies of our reportable segments are the same as those described in Note 2, Summary of Significant Accounting Policies . Our chief operating decision maker allocates resources to our business segments and assesses segment performance based on segment profit (loss), which consists of revenues less cost of revenues, selling and marketing and distribution expenses. The following summarizes the operating performance of our reportable segments (in thousands): System One In-Center Other Services Intersegment Elimination Total Year Ended December 31, 2017 Revenues from external customers $ 301,299 $ 61,307 $ 11,796 $ 19,539 $ — $ 393,941 Intersegment Revenues 5,062 — — — (5,062 ) — Revenues 306,361 61,307 11,796 19,539 (5,062 ) 393,941 Segment profit (loss) 82,585 8,070 (80,804 ) (23,702 ) — (13,851 ) Depreciation and amortization 22,166 2,121 4,349 5,217 (99 ) 33,754 Segment assets 134,825 25,225 146,737 19,712 (870 ) 325,629 Year Ended December 31, 2016 Revenues from external customers $ 276,393 $ 63,038 $ 12,166 $ 14,781 $ — $ 366,378 Intersegment Revenues 7,530 — — — (7,530 ) — Revenues 283,923 63,038 12,166 14,781 (7,530 ) 366,378 Segment profit (loss) 74,912 10,092 (62,309 ) (26,233 ) (747 ) (4,285 ) Depreciation and amortization 23,671 2,003 4,427 4,781 (2,245 ) 32,637 Segment assets 135,038 21,246 138,273 23,620 (970 ) 317,207 Year Ended December 31, 2015 Revenues from external customers $ 244,641 $ 74,768 $ 10,302 $ 6,412 $ — $ 336,123 Intersegment Revenues 3,134 — — — (3,134 ) — Revenues 247,775 74,768 10,302 6,412 (3,134 ) 336,123 Segment profit (loss) 59,748 12,395 (62,946 ) (23,826 ) — (14,629 ) Depreciation and amortization 20,554 1,835 5,004 3,322 — 30,715 Segment assets 120,253 24,232 142,842 19,547 — 306,874 The following table presents a reconciliation of the total segment assets to total assets (in thousands): December 31, 2017 2016 Total segment assets $ 179,762 $ 179,904 Intersegment elimination (870 ) (970 ) Corporate assets: Cash and cash equivalents 64,927 59,632 Accounts Receivable, net 949 632 Inventory 305 — Property and equipment, net 16,628 16,600 Intangible assets, net 7,660 9,688 Goodwill 42,748 42,648 Prepaid and other assets 13,520 9,073 Total assets $ 325,629 $ 317,207 Long-lived tangible assets consist of property and equipment, net and field equipment, net. The following table presents total long-lived tangible assets by geographic area (in thousands): December 31, 2017 2016 2015 United States $ 42,610 $ 46,724 $ 46,551 Mexico 16,790 13,431 14,233 Other Americas 1,630 571 825 Total Americas 61,030 60,726 61,609 Germany 18,270 17,574 19,053 Other Europe 5,226 5,754 6,793 Total Europe 23,496 23,328 25,846 Total $ 84,526 $ 84,054 $ 87,455 Deferred cost of revenues, net are primarily located in the United States. Substantially all of our revenues are derived from the sale of the System One and related products, which cannot be used with any other dialysis system, and from needles and blood tubing sets in the U.S. The following table summarizes the number of customers who individually make up greater than ten percent of total revenues: Years Ended December 31, 2017 2016 2015 DaVita 20 % 20 % 20 % Fresenius 20 % 18 % 17 % Sales to DaVita and Fresenius are in the System One segment.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Minimum Purchase Commitments We have agreements with certain of our suppliers, primarily for the purchase of fluids for our System One segment and needles for our In-Center segment, that include minimum purchase commitments. As of December 31, 2017 , we had a total of $20.3 million in minimum purchase commitments under these agreements, $9.6 million over the next year, $10.0 million over the next one to two years and $0.7 million over the next four to five years. Operating Leases Our operating leases relate to our corporate headquarters and NxStage Kidney Care facilities, as well as our foreign leased manufacturing facilities in Mexico, Germany and Italy. Our corporate headquarters lease has an initial term of eleven years through mid- 2023 with an early termination provision after seven years, subject to certain terms and conditions, with two 5 -year options to extend beyond the initial term on substantially the same terms and at rent equal to ninety-five percent of the then fair market value. The lease included a tenant improvement allowance of $4.3 million . Our NxStage Kidney Care facility lease agreements have initial lease terms expiring from 2018 to 2028 , and contain renewal options ranging from five to ten years at the fair rental value at the time of renewal. The leases are generally subject to periodic consumer price index increases or contain fixed escalation clauses and include tenant improvement allowances ranging from $0.1 million to $0.3 million per facility. Our foreign leased manufacturing facilities are subject to lease agreements with termination dates through 2021 and contain renewal options at the fair rental value at the time of renewal. Our lease agreements contain certain provisions that require us to pay executor costs such as real estate taxes, operating expenses and common utilities. Rent expense is recorded on a straight-line basis over the lease term. Tenant improvement allowances are recorded as a deferred rent obligation and amortized to rent expense over the term of the lease. Rent expense under our operating leases was $5.3 million , $5.0 million and $4.5 million during 2017 , 2016 and 2015 , respectively. The future minimum rental payments as of December 31, 2017 under our operating leases are as follows (in thousands): 2018 $ 5,463 2019 4,811 2020 4,297 2021 3,694 2022 3,174 Thereafter 2,708 $ 24,147 Legal Contingencies From time to time, during the ordinary course of operations, we are party to litigation and arbitration and are subject to investigations relating to various aspects of our business. We regularly analyze current information about such claims for probable losses and provide accruals for such matters, including the estimated legal expenses and consulting services in connection with these matters, as appropriate. We utilize our internal legal department as well as external resources for these assessments. In making the decision regarding the need for loss accrual, we consider the degree of probability of an unfavorable outcome and our ability to make a reasonable estimate of the amount of loss. In management's opinion, we are not currently involved in any legal proceedings which, individually or in the aggregate, are reasonably likely to have a material adverse effect on our financial condition or results of operations.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Tax Reform, which was signed into law on December 22, 2017, has resulted in significant changes to the U.S. corporate income tax system. The Tax Reform reduces the corporate income tax rate from 35% to 21%, requires companies to pay a one-time transaction tax on earnings of certain foreign subsidiaries that were previously tax deferred and creates new taxes on certain foreign sourced earnings. The effects of changes in tax rates and laws are recognized in the period in which the new legislation is enacted subject to Staff Accounting Bulletin 118 which provides for a measurement period to complete the accounting for certain elements of the tax reform. We have not yet completed our evaluation of the impact of the Tax Reform on our financial statements; however, we have remeasured assets at December 31, 2017 based on the new Federal income tax rate of 21%. We will continue to make and refine our calculations as additional analysis is completed. In addition, our estimates may also be affected as we gain a more thorough understanding of the Tax Reform. The following is a summary of income (loss) before income taxes by geography (in thousands): Years Ended December 31, 2017 2016 2015 U.S. $ (19,314 ) $ (9,265 ) $ (17,672 ) Foreign 3,844 3,050 2,489 Total $ (15,470 ) $ (6,215 ) $ (15,183 ) The components of the provision for income taxes are as follows (in thousands): Years Ended December 31, 2017 2016 2015 Current: U.S. - Federal $ (1,269 ) $ — $ — U.S. - State 96 73 86 Foreign 1,540 1,200 1,225 Total Current 367 1,273 1,311 Deferred: Foreign (512 ) (171 ) (234 ) Total Deferred (512 ) (171 ) (234 ) Total Provision $ (145 ) $ 1,102 $ 1,077 We recognized a provision for income taxes during each of 2017 , 2016 and 2015 related to the profitable operations of certain foreign subsidiaries. However, the provision recognized during 2017 includes the impact of an allocation of U.S. tax expense between continuing operations and total other comprehensive income (loss) (Intraperiod Tax Allocation). Such allocation resulted in a decrease to the provision for income taxes of $1.3 million during 2017. This allocation has no impact on total comprehensive loss or total stockholders' equity for 2017. A reconciliation of the U.S. federal statutory tax rate to the effective tax rate is as follows: Years Ended December 31, 2017 2016 2015 Federal statutory rate 34.0 % 34.0 % 34.0 % Stock compensation 25.7 % (1.5 )% (2.5 )% State income tax, net of federal tax benefit 2.3 % (2.3 )% (2.8 )% U.S. research credits 6.7 % 18.9 % (0.3 )% Foreign income inclusion in the U.S. (4.7 )% (10.4 )% (5.0 )% Valuation allowance 149.4 % (47.4 )% (25.8 )% Change in tax reserves (1.4 )% (0.5 )% (0.5 )% Minority Interest (1.6 )% (15.9 )% (0.9 )% Tax Reform impact (344.6 )% — % — % Intraperiod tax allocation 8.2 % — % — % ASU 2016-09 126.7 % — % — % Other, net 0.2 % 7.4 % (3.3 )% Effective tax rate 0.9 % (17.7 )% (7.1 )% We remeasured certain deferred tax assets and liabilities based on the new Federal income tax rate of 21%. Such remeasurement resulted in a one-time net decrease of approximately $53 million to our U.S. deferred tax assets and liabilities with a corresponding decrease to our valuation allowance. This change represents our best estimate of the effects of the Tax Reform at the time of the preparation of this Annual Report on Form 10-K. The actual impact is subject to change from these estimates and such change may be significant, pending the completion of our analysis of certain aspects of the Tax Reform and refining our calculations. Effective January 1, 2017 we adopted ASU No. 2016-09: “Improvements to Employee Share-Based Payment Accounting” (ASU 2016-09) which resulted in an increase in our gross U.S. federal and state net operating loss carryforwards net operating loss carryforwards deferred tax asset of $52.9 million and $34.3 million , respectively, with a corresponding increase to our valuation allowance. Deferred income tax assets and liabilities reflect the tax effects of differences in the recognition of income and expense items for tax and financial reporting purposes. Deferred tax assets (liabilities) are made up of the following (in thousands): December 31, 2017 2016 Deferred tax assets: Net operating loss carryforwards $ 92,315 $ 115,151 Tax credits 12,706 11,180 Stock-based compensation 4,922 7,339 Capitalized research and development 1,126 2,167 Financing liabilities 5,531 5,161 Other 7,613 8,349 Total deferred tax assets 124,213 149,347 Deferred tax liabilities: Fixed assets (5,485 ) (5,754 ) Intangible assets (1,902 ) (3,606 ) Other (222 ) (187 ) Total deferred tax liabilities (7,609 ) (9,547 ) Net deferred tax assets before valuation allowance 116,604 139,800 Less valuation allowance (115,035 ) (138,795 ) Net deferred tax assets $ 1,569 $ 1,005 As of December 31, 2017 , we had gross U.S. federal and state net operating loss carryforwards of approximately $390 million and $182 million , respectively, available to offset future taxable income. The federal and state net operating loss carryforwards will expire between 2018 and 2037 if not utilized. We also had federal and state research and development credit carryforwards of $8.5 million and $3.0 million ( $3.9 million gross), respectively, which begin to expire in 2020 if not utilized. We also had foreign tax credits of approximately $1.0 million that will expire between 2018 and 2021 if not utilized. All years remain open for examination by the United States Internal Revenue Service (IRS) due to the losses incurred and years 2011 through 2017 remain open for examination in the various states and non-US tax jurisdictions in which we files tax returns. During 2017 , the valuation allowance decreased by approximately $23.8 million , primarily due to the reduction in our deferred tax assets resulting from remeasuring them at the new Federal income tax rate, offset in part by an increase in our net operating loss carryfowards resulting from the adoption of ASU 2016-09. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A full valuation allowance has been recorded in the accompanying consolidated financial statements to offset our U.S. and specific foreign deferred tax assets because the future realizability of such assets is uncertain. In assessing the realizability of deferred tax assets we consider, among other things, the expected reversal of deferred tax liabilities and projected future taxable income. Valuation allowances are reversed only when we have adequate history of taxable income and projections for future taxable income. We believe that the future realization of these assets is not more likely than not given the expected future tax losses in these jurisdictions. Under the provisions of the Internal Revenue Code, the net operating loss and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. Net operating loss and tax credit carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a three-year period in excess of 50 percent, as defined under Sections 382 and 383 of the Internal Revenue Code, respectively, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on the value of the Company immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation in future years. The Company has completed several financings since its inception which it believes has resulted in a change in control as defined by Sections 382 and 383 of the Internal Revenue Code. We believe $1.5 million of our net operating losses will expire unused due to limitations. For applicable years, the Company generated research credits but has not conducted a study to document its qualified activities. This study may result in an adjustment to the Company’s research and development credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the deferred tax asset established for the research and development credit carry-forwards and the valuation allowance. The below table details the changes in unrecognized tax benefits, which if recognized would favorably impact our effective tax rate (in thousands): Years Ended December 31, 2017 2016 2015 Balance at beginning of the year $ 517 $ 379 $ 347 Increase in unrecognized tax benefits as a result of tax positions taken during the current year 275 89 66 Increase (decrease) in unrecognized tax benefits as a result of tax positions taken during a prior year 50 115 (34 ) Reductions due to lapse of applicable statute of limitations (78 ) (66 ) — Balance at end of year $ 764 $ 517 $ 379 As of December 31, 2017 , we had a liability for unrecognized tax benefits included in the balance sheet of approximately $0.8 million , all of which would impact our effective tax rate if recognized. We had less than $0.1 million accrued as of December 31, 2017 , 2016 and 2015 for interest and penalties related to unrecognized tax benefits. We monitor the undistributed earnings of foreign subsidiaries and, as necessary, provide for income taxes on those earnings that are not deemed permanently invested. As of December 31, 2017 , there were no significant undistributed earnings of foreign subsidiaries that were deemed permanently invested.

Stock Plans and Stock-Based Com

Stock Plans and Stock-Based Compensation	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Plans and Stock-Based Compensation	Stock Plans and Stock-Based Compensation Stock Incentive Plans We maintain the 2014 Omnibus Incentive Plan (2014 Plan) that governs awards to both employees and non-employees. The 2014 Plan replaced and superseded our 2005 Stock Incentive Plan (2005 Plan) except that awards granted under the 2005 Plan remain in effect pursuant to their original terms. While the 2014 Plan authorizes a variety of equity-based and cash awards, we generally offer equity incentives under the 2014 Plan in the form of restricted stock units, stock options and performance shares. Restricted stock units customarily vest over a period of three or four years. Stock options expire ten years from the date of grant and customarily vest over a period of four years for employees and one year for members of our Board of Directors. Performance shares are issued to certain employees and executive officers and entitle recipients to earn restricted stock units based on the achievement of annual corporate financial performance metrics; any earned restricted stock units customarily vest over a period of three years. We settle stock option exercises and the vesting of restricted stock units with newly issued common shares. Pursuant to the 2014 Plan, each share award other than options or stock appreciation rights will reduce the number of total shares available for grant by 1.62 shares. A total of 5.6 million shares, together with any unissued shares that may carry over from the 2005 Plan, have been authorized for grant under the 2014 Plan and at December 31, 2017 , 7.8 million shares remained available for future grant. We also maintain the 2005 Employee Stock Purchase Plan (2005 Purchase Plan), which authorizes the issuance of up to 0.9 million shares of common stock to participating employees through a series of periodic offerings. Each six -month offering period begins in January and July. An employee becomes eligible to participate in the 2005 Purchase Plan once he or she has been employed for at least three months and is regularly employed for at least 20 hours per week for more than three months in a calendar year. The price at which employees can purchase common stock in an offering is 95 percent of the closing price of our common stock on the NASDAQ Global Select Market on the lower of the first or last day of the offering period, unless otherwise determined by the Board of Directors or Compensation Committee of the Board. As of December 31, 2017 , 0.2 million shares were available for future issuance under the 2005 Purchase Plan. Stock Options A summary of the status of stock options granted under all of our plans at December 31, 2017 , and changes during the year then ended, is as follows: Stock Options Shares Weighted Average Exercise Price Aggregate Intrinsic Value Average Remaining Contractual Life (In thousands) (In years) Outstanding at beginning of year 4,656,405 $ 15.02 Granted 675,358 $ 26.87 Exercised (1,130,939 ) $ 13.79 Forfeited or expired (83,627 ) $ 20.50 Outstanding at end of year 4,117,197 $ 17.19 $ 30,825 6.75 Fully vested and exercisable 2,684,405 $ 15.90 $ 22,730 6.05 Fully vested, exercisable and expected to vest 4,002,574 $ 17.12 $ 30,177 6.71 The aggregate intrinsic value for stock options is calculated based on the market price of our common stock as of December 31, 2017 , less the exercise price of the underlying awards, excluding out-of-the-money awards. The total fair value of options that vested during 2017 , 2016 and 2015 was $6.7 million , $6.1 million and $4.8 million , respectively. The aggregate intrinsic value of options exercised during 2017 , 2016 and 2015 was $15.3 million , $5.6 million and $10.4 million , respectively. The aggregate intrinsic value of options exercised is calculated based on the market price of our common stock on the exercise date, less the exercise price of underlying award. The weighted-average fair value of options granted during 2017 , 2016 and 2015 was $9.92 , $5.89 and $6.16 per option, respectively. The fair value of options at date of grant was estimated using the Black-Scholes option-pricing model with the following assumptions: Years Ended December 31, 2017 2016 2015 Expected life (in years) 5.00 to 6.50 5.00 to 9.92 4.80 to 10.00 Risk-free interest rate 1.79% to 2.13% 1.20% to 2.45% 1.34% to 2.27% Expected stock price volatility 36.8% to 38.8% 38% to 43.05% 38% to 42.52% Expected dividend yield — — — Restricted Stock In March 2017, the Compensation Committee of our Board of Directors approved the grant of up to 231,384 restricted stock units subject to the achievement of certain Company financial performance metrics for the year ending December 31, 2017 (2017 Performance Awards). In August 2017, in connection with the Board of Director's approval of the Merger, the Compensation Committee determined that all Company financial performance metrics for the 2017 Performance Awards shall be deemed fully satisfied to enhance the retention features of such awards in light of the pending Merger. These restricted stock units vest over a requisite service period of three years, subject to full acceleration upon Merger completion, and have a modified grant date fair value of $23.14 per unit. The total fair value of restricted stock that vested was $4.8 million , $5.1 million and $5.5 million during 2017 , 2016 and 2015 , respectively. The weighted-average fair value of restricted stock granted during 2017 , 2016 and 2015 was $25.10 , $16.33 and $16.71 per unit, respectively. The following table summarizes the status of the unvested restricted stock: Shares Weighted Average Grant-date Fair Value Aggregate Intrinsic Value Weighted Average Remaining Contractual Life (In thousands) (In years) Unvested at December 31, 2016 1,143,800 $ 15.57 Granted 407,279 $ 25.10 Vested (339,496 ) $ 14.24 Forfeited (499,253 ) $ 16.26 Unvested at December 31, 2017 712,330 $ 21.17 $ 17,260 2.14 The aggregate intrinsic value for restricted stock is calculated based on the market price of our common stock as of December 31, 2017 . Employee Stock Purchase Plan The weighted-average fair value of stock purchase rights granted as part of the 2005 Purchase Plan during 2017 , 2016 and 2015 was $4.06 , $4.07 and $1.74 per share, respectively. The fair value of the employees' stock purchase rights was estimated using the Black-Scholes option-pricing model with the following assumptions: Years Ended December 31, 2017 2016 2015 Expected life (in months) 6 6 6 Risk-free interest rate 0.65% to 1.13% 0.37% to 0.49% 0.11% to 0.13% Expected stock price volatility 36.4% to 39.2% 39.6% to 48.2% 18.4% to 22.4% Expected dividend yield — — — There were 36,253 , 37,531 and 50,343 shares issued under the 2005 Purchase Plan during 2017 , 2016 and 2015 , respectively, which resulted in share-based compensation expense of $0.1 million in 2017 , $0.2 million in 2016 and $0.1 million in 2015 . Stock-based Compensation Expense The following table presents stock-based compensation expense included in the consolidated statements of comprehensive loss (in thousands): Years Ended December 31, 2017 2016 2015 Cost of revenues $ 1,201 $ 1,371 $ 1,068 Selling and marketing 3,933 3,304 4,458 Research and development 1,539 1,536 1,979 General and administrative 4,864 3,906 5,093 Total stock-based compensation expense $ 11,537 $ 10,117 $ 12,598 As of December 31, 2017 , approximately $20.2 million of unrecognized stock compensation cost related to nonvested stock options and restricted stock (net of estimated forfeitures) is expected to be recognized over a weighted-average period of 2.7 years.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Employee Benefit Plans	Employee Benefit Plans 401(k) Retirement Plan We have a 401(k) retirement plan (401(k) Plan) for the benefit of eligible employees, as defined. Each participant may elect to contribute up to 75% of his or her compensation to the 401(k) Plan each year, subject to certain IRS limitations. We contribute 100% of the first 3% of the employee's contribution and 50% of the next 2% of the employee's contribution. We contributed $2.7 million , $2.5 million and $1.8 million to the 401(k) Plan during 2017 , 2016 and 2015 , respectively. Other Compensation Plans We maintain postemployment benefit plans for employees in certain foreign subsidiaries. These unfunded plans provide lump sum benefits, payable based on statutory regulations for voluntary or involuntary termination. We have recorded a liability of $2.1 million and $1.7 million as of December 31, 2017 and 2016 , respectively, as other long-term liabilities for costs associated with these plans. The expense recorded in connection with these plans was not significant during 2017 , 2016 and 2015 .

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	Stockholders' Equity We received 110,510 , 114,301 and 49,786 shares of common stock that were surrendered in payment for the exercise of stock options during 2017 , 2016 and 2015 , respectively.

Noncontrolling Interests

Noncontrolling Interests	12 Months Ended
	Dec. 31, 2017
Noncontrolling Interest [Abstract]
Noncontrolling Interests	Noncontrolling Interests Noncontrolling interests represent the third-party equity ownership interests in consolidated entities for which we have effective control, including variable interest entities (VIE) for which we are deemed the primary beneficiary. We assess the terms of our investment interests to determine if any of our investees meet the definition of a VIE. For any VIEs, we perform an analysis to determine whether our variable interests give us a controlling financial interest in a VIE. The analysis identifies the primary beneficiary of a VIE as the enterprise that has both 1) the power to direct activities of a VIE that most significantly impact the entity’s economic performance and 2) the obligation to absorb losses of the entity or the right to receive benefits from the entity. As of December 31, 2017 , we have 5 VIEs included in our consolidated financial statements all of which are NxStage Kidney Care dialysis centers. We are the managing member or we have a majority seat on the entity’s board of managers and manage these entities through a management services agreement. The analysis upon which these consolidation determinations rest are complex, involve uncertainties, and require significant judgment on various matters. At December 31, 2017 and 2016 , total assets of our VIEs were $5.6 million and $8.0 million , and total liabilities and noncontrolling interests of our VIEs were $5.8 million and $7.2 million , respectively. We have potential obligations to purchase the noncontrolling interests held by third parties in certain of our consolidated subsidiaries. These obligations are in the form of put provisions and are contingently exercisable at the third-party owners' discretion given specific facts and circumstances as outlined in each specific put provision. If these put provisions were exercised, we would be required to purchase all the third-party owners' noncontrolling interests at a fair value at the time of exercise pursuant to the terms of the agreement. At December 31, 2017 the Company's noncontrolling interests subject to put provisions were not material and none of the rights were exercisable. The following table sets forth the changes in noncontrolling interest not subject to put provisions for the periods indicated (in thousands): Years Ended December 31, 2017 2016 2015 Balance at beginning of period $ 625 $ 1,694 $ 1,088 Capital contributions by noncontrolling interest — 630 1,316 Sales of noncontrolling interests — 679 208 Add: Accretion to redemption value of noncontrolling interests 481 — — Reclassification of noncontrolling interest subject to put provision 322 — — Net loss attributable to noncontrolling interest in consolidated subsidiary (1,440 ) (2,378 ) (918 ) Balance at end of period $ (12 ) $ 625 $ 1,694

Derivative Instruments and Hedg

Derivative Instruments and Hedging	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging	Derivative Instruments and Hedging We operate manufacturing and service facilities in Mexico, Germany, and Italy and we purchase materials and pay our employees at those facilities in pesos and euros, and as such, we are potentially exposed to adverse as well as beneficial movements in currency exchange rates. We enter into foreign exchange forward contracts to minimize the impact of currency exchange rate fluctuations on these peso and euro denominated expenses. These contracts have durations of up to twelve months and are designated as cash flow hedges. The counterparties to these foreign exchange forward contracts are creditworthy financial institutions; therefore, we do not consider the risk of counterparty nonperformance to be material. The notional amount of our outstanding contracts that are designated as cash flow hedges was $24.1 million and $18.6 million at December 31, 2017 and December 31, 2016 , respectively. The fair value of these contracts is recorded on the balance sheet within prepaid expenses and other current assets or accrued expenses depending on the gain (loss) position. The fair value of these contracts was an asset of less than $0.1 million at December 31, 2017 and a liability of $1.8 million at December 31, 2016 , respectively. The cash flows related to our currency exchange contracts are classified as operating cash flows, which is consistent with the cash flow treatment of the underlying items being hedged. Gains or losses related to hedge ineffectiveness recognized in earnings were not material during 2017 , 2016 or 2015 . Given the short-term nature of our contracts, any gains or losses recorded within accumulated other comprehensive income (loss) will be recognized in earnings within the next twelve months. The following table presents the effect of these contracts designated as cash flow hedges on our consolidated financial statements (in thousands): Gain (Loss) Recognized in OCI (Effective Portion) Gain (Loss) Reclassified from OCI into Income (Effective Portion) Classification within the Condensed Consolidated Statement of Comprehensive Loss Year Ended December 31, 2017 Foreign exchange forward contracts $ 3,433 $ 1,163 Cost of revenues Year Ended December 31, 2016 Foreign exchange forward contracts $ (2,712 ) $ (1,910 ) Cost of revenues Year Ended December 31, 2015 Foreign exchange forward contracts $ (2,140 ) $ (1,745 ) Cost of revenues

Accumulated Other Comprehensive

Accumulated Other Comprehensive (Loss) Income	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Accumulated Other Comprehensive (Loss) Income	Accumulated Other Comprehensive (Loss) Income The following additional information is provided with respect to the accumulated other comprehensive (loss) income as presented on the condensed consolidated balance sheets (in thousands): Unrealized gain (loss) on derivative instruments Other (2) Total Balance, net of tax, as of December 31, 2014 $ (1,088 ) $ (1,104 ) $ (2,192 ) Other comprehensive income before reclassifications (2,140 ) (1,444 ) (3,584 ) Loss reclassified to earnings (1) 1,745 — 1,745 Total other comprehensive income (loss) (395 ) (1,444 ) (1,839 ) Balance, net of tax, as of December 31, 2015 $ (1,483 ) $ (2,548 ) $ (4,031 ) Other comprehensive income before reclassifications (2,712 ) (1,268 ) (3,980 ) Gain reclassified to earnings (1) 1,910 — 1,910 Total other comprehensive income (loss) (802 ) (1,268 ) (2,070 ) Balance, net of tax, as of December 31, 2016 $ (2,285 ) $ (3,816 ) $ (6,101 ) Other comprehensive income before reclassifications, net of $1,269 tax during 2017 2,164 1,427 3,591 Gain/Loss reclassified to earnings (1) (1,163 ) — (1,163 ) Total other comprehensive income (loss) 1,001 1,427 2,428 Balance, net of tax, as of December 31, 2017 $ (1,284 ) $ (2,389 ) $ (3,673 ) (1) Reclassifications of gains (losses) on derivative instruments are included in cost of revenues on the consolidated statement of comprehensive loss. See Note 16, Derivative Instruments and Hedging for further information. (2) Other includes cumulative translation adjustments and, to a lesser extent, pension benefits.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements We measure the fair value of our foreign exchange forward contracts classified as derivative instruments using an income approach, based on prevailing market forward rates less the contract rate multiplied by the notional amount. The product of this calculation is then adjusted for counterparty risk. We did not have any transfers between Level 1 and Level 2 and Level 3 during the twelve months ended December 31, 2017 . The following tables present assets and liabilities measured at fair value on a recurring basis and their level within the value hierarchy (in thousands): December 31, 2017 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Fair Value Assets Money market funds (1) $ 35,020 $ — $ — $ 35,020 Foreign exchange forward contracts (2) — 690 — 690 Liabilities Foreign exchange forward contracts (2) $ — $ 661 $ — $ 661 December 31, 2016 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Total Fair Value Assets Money market funds (1) $ 34,804 $ — $ — $ 34,804 Foreign exchange forward contracts (2) — — — — Liabilities Foreign exchange forward contracts (2) $ — $ 1,771 $ — $ 1,771 (1) Money market funds are included within cash and cash equivalents. (2) Foreign exchange forward contracts are included within prepaid expenses and other current assets or accrued expenses depending on the gain (loss) position. The carrying amount of our long-term debt approximates fair value at December 31, 2017 . The fair value of our long-term debt was estimated using inputs derived principally from market observable data, including current rates offered to us for debt of the same or similar remaining maturities. Within the hierarchy of fair value measurements, these are Level 2 inputs. The carrying amounts reflected in the consolidated balance sheets for cash and cash equivalents (including money market funds), accounts receivable, prepaid expenses and other current and non-current assets, accounts payable and accrued expenses approximate fair value due to their short-term nature. In 2017, we acquired a 2.5% equity ownership of a privately held dialysis services company in exchange for $2.5 million in cash. This investment is accounted for using the cost method as we are unable to exercise any significant influence over the company. The investment has been recorded at historical cost, classified within other assets on our condensed consolidated balance sheet, and is reviewed for events or changes in circumstances that may have a significant adverse effect on the fair value of the investment. There have been no changes in circumstances or identified events that may have a significant adverse effect on the fair value.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	12 Months Ended
	Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	Supplemental Cash Flow Information The following additional information is provided with respect to the consolidated statements of cash flows (in thousands): Years Ended December 31, 2017 2016 2015 Supplemental Disclosures: Cash paid for interest $ 638 $ 639 $ 703 Cash paid for taxes 1,258 983 919 Noncash Investing and Financing Activities: Transfers from inventory to field equipment $ 19,257 $ 20,920 $ 16,675 Transfers from field equipment to deferred cost of revenues 11,026 13,400 11,638 Payment of corporate bonus plan in common stock — — 1,103 Market value of shares received in payment for exercise of stock options 3,100 2,320 875 Construction-in-process financed by construction liability 142 187 1,332 Redemption of noncontrolling interest 481 — — Property and equipment acquired under capital lease — 127 354 Acquisition of business — — 513 Increase in deferred revenues related to the new manufacturing facility in Germany — — 663 Capital contributions by noncontrolling interest — 54 325

Quarterly Financial Data (Unaud

Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data (Unaudited)	Quarterly Financial Data (Unaudited) The following table sets forth selected quarterly information (unaudited) (in thousands, except per share data): Three Months Ended March 31, June 30, September 30, December 31, Revenues $ 96,829 $ 96,216 $ 97,295 $ 103,601 Gross profit 41,190 41,166 40,607 45,325 Loss from operations (1,681 ) (2,056 ) (8,283 ) (1,831 ) Net loss (1,541 ) (2,579 ) (8,894 ) (2,311 ) Net loss attributable to stockholders of NxStage Medical, Inc. (1,189 ) (2,089 ) (8,445 ) (2,269 ) Net loss attributable to common stockholders (1,189 ) (2,089 ) (8,926 ) (2,269 ) Net loss per share, basic and diluted $ (0.02 ) $ (0.03 ) $ (0.14 ) $ (0.03 ) Three Months Ended March 31, June 30, September 30, December 31, Revenues $ 89,207 $ 92,207 $ 91,951 $ 93,013 Gross profit 36,517 38,423 39,181 37,864 Loss from operations (975 ) (1,180 ) 24 (2,154 ) Net loss (1,783 ) (2,225 ) (890 ) (2,419 ) Net loss attributable to stockholders of NxStage Medical, Inc. (1,276 ) (1,732 ) (166 ) (1,597 ) Net loss attributable to common stockholders (1,276 ) (1,732 ) (166 ) (1,597 ) Net loss per share, basic and diluted $ (0.02 ) $ (0.03 ) $ (0.00 ) $ (0.02 )

Summary of Significant Accoun27

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements of NxStage Medical, Inc. have been prepared in accordance with accounting principles generally accepted in the United States of America (U.S. GAAP) and with the requirements of Regulation S-X.
Use of Estimates	The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and 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. Actual results could differ from those estimates. Such financial statements reflect all adjustments that, in the opinion of management, are necessary for a fair presentation of the results of the periods presented. All such adjustments are of a normal recurring nature.
Principles of Consolidation	Principles of Consolidation Our consolidated financial statements include the accounts of NxStage Medical, Inc. and our wholly-owned subsidiaries and other entities in which we maintain a majority voting interests or for which we maintain effective control including variable interest entities (VIEs) for which we are deemed the primary beneficiary. All significant intercompany balances and transactions have been eliminated. Noncontrolling interests represent the proportionate equity interests in the consolidated entities that are not wholly owned by us. Noncontrolling interests of acquired entities are recognized at their initial fair value.
Revenue Recognition	Revenue Recognition We recognize revenue from product sales and services when earned. Revenues are recognized when: (a) there is persuasive evidence of an arrangement, (b) the product has been shipped or services and supplies have been provided to the customer, (c) the sales price is fixed or determinable and (d) collection is reasonably assured. Certain agreements with distributors allow for product returns and credits. For shipment of product sold to distributors, revenue is recognized at the time of sale if a reasonable estimate of future returns or credit can be made. If a reasonable estimate of future returns or credit cannot be made, we recognize revenue using the "sell-through" method. Under the "sell-through" method, revenue and related costs of revenue is deferred until the final resale of such products to end customers. In addition to contractually determined volume discounts, in many agreements we offer rebates based on sales to specific end customers and discounts for early payment. Rebates and discounts are recorded as a reduction of sales and trade accounts receivable, based on our best estimate of the amount of probable future rebate or discount on current sales. We enter into multiple-element arrangements that may include a combination of equipment, related disposables and services. Revenue arrangements with multiple elements are divided into separate units of accounting if specified criteria are met, including whether the delivered element has stand-alone value to the customer, the consideration received is allocated among the separate units based on their respective selling price, and the applicable revenue recognition criteria are applied to each of the separate units. We determine selling price using vendor specific objective evidence (VSOE), if it exists, otherwise third-party evidence of selling price is used. If neither VSOE nor third-party evidence of selling price exists for a unit of accounting, we use best estimated selling price (BESP). We generally expect that we will not be able to establish third-party evidence due to the nature of our products and the markets in which we compete, and, as such, we typically will determine selling price using VSOE or BESP. We determine BESP for an individual element based on consideration of both industry and Company-specific factors, including the selling price and profit margin for similar products, the cost to produce the deliverable and the anticipated margin on that deliverable and the characteristics of the varying markets in which the deliverable is sold. Any tax assessed by a governmental authority that is incurred as a result of a revenue transactions (e.g. sales tax) is excluded from revenues and reported on a net basis System One Segment We derive revenue in the home market from sales of the System One equipment and/or PureFlow SL hardware and sales of disposable products. For the System One equipment and PureFlow SL hardware sales transactions, sold to dialysis clinic customers in the home market, due to the depot service model whereby equipment requiring service is picked up and a replacement device is shipped to the site of care, we recognize upfront fees received from equipment sales transactions as revenue on a straight-line basis over the expected term of our remaining service obligation and direct costs relating to the delivered equipment are classified in deferred cost of revenues and amortized over the same expected period as the related revenue. Disposable products revenue is recognized on a monthly basis. We also offer a month-to-month System One equipment and PureFlow SL hardware rental arrangements. Under these arrangements, revenue is recognized on a monthly basis in accordance with agreed upon contract terms and pursuant to binding customer purchase orders and fixed payment terms. Our sales arrangements with our international distributors are structured as direct product sales and have no significant post-delivery obligations with the exception of standard warranty obligations. Revenue from direct product sales is recognized upon delivery in accordance with contract terms. In the critical care market, we structure sales of the System One and disposable products as direct product sales and have no significant post-delivery obligations with the exception of standard warranty obligations. Revenue from direct product sales is recognized upon delivery in accordance with contract terms. Certain of these arrangements provide for training, technical support and extended warranty services to our customers. We recognize training and technical support revenue when the related services are performed. In the case of extended warranty, the service revenue is recognized ratably over the extended warranty period. In-Center Segment Our In-Center segment sales are structured as direct product sales primarily through distributors, and we have no significant post delivery obligations with the exception of standard warranty obligations. Revenue from direct product sales is recognized upon delivery in accordance with contract terms. Services Segment Revenues in our Services segment are derived from dialysis care services provided to patients at our NxStage Kidney Care dialysis centers. Revenues are recognized based on a customary fee schedule, net of estimated contractual allowances to reflect the estimated amounts to be received from the payor. Revenues are recognized in the period in which services are provided when we have the ability to reasonably estimate amounts ultimately collectible from the payor. In instances where we do not have the ability to reasonably estimate amounts ultimately collectible, as is often the case with non-contracted commercial health plans and amounts due from patients (including co-pay and deductible amounts), revenue is recognized in the period in which cash is received.
Foreign Currency Translation and Transactions	Foreign Currency Translation and Transactions Assets and liabilities of our foreign operations are translated into U.S. dollars at current exchange rates, and income and expense items are translated at average rates of exchange prevailing during the year. Foreign exchange gains and (losses) on intercompany loans considered permanent investments are recorded in other comprehensive loss. Gains and (losses) realized from transactions denominated in foreign currencies, including intercompany balances not considered permanent investments, are included in the consolidated statements of comprehensive loss within other income (expense), net.
Cash and Cash Equivalents	Cash and Cash Equivalents We consider all highly-liquid investments purchased with original maturities of 90 days or less to be cash equivalents. Cash equivalents include amounts invested in treasury obligation money market funds. Cash equivalents are stated at cost plus accrued interest, which approximates fair value.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject us to concentrations of credit risk consist principally of cash and cash equivalents, derivatives and accounts receivable. To mitigate such risk, with respect to cash and cash equivalents, we place our cash in bank deposit accounts with financial institutions that have investment grade ratings and capital ratios exceeding minimum Federal Reserve Adequacy Guidelines and in treasury obligation money market funds. To mitigate concentration of credit risk with respect to derivatives we enter into transactions with highly-rated financial institutions and frequently monitor the credit worthiness of our counterparties. Concentration of credit risk with respect to accounts receivable is primarily limited to certain customers to whom we make substantial sales. No customer represented more than 10% of accounts receivable at December 31, 2017 and two customers represented 12% and 10% of accounts receivable at December 31, 2016 . To reduce risk, we routinely assess the financial strength of our customers and closely monitor their amounts due and, as a result of our assessment, we believe that our accounts receivable credit risk exposure is limited. Historically, we have not experienced any significant credit losses related to an individual customer or group of customers in any particular market or geographic area. We maintain an allowance for doubtful accounts based on an analysis of historical losses from uncollectible accounts, aging of unpaid accounts receivable balances and risks identified for specific customers who may not be able to make required payments. Provisions for the allowance for doubtful accounts are recorded in general and administrative expenses in the accompanying consolidated statements of comprehensive loss. Activity related to allowance for doubtful accounts consisted of the following (in thousands): Year Ended Balance at Beginning of Year Provision Write-offs Balance at End of Year December 31, 2017 $ 535 $ 471 $ (191 ) $ 815 December 31, 2016 $ 417 $ 179 $ (61 ) $ 535 December 31, 2015 $ 425 $ 20 $ (28 ) $ 417 We use and are dependent upon a number of single source suppliers of raw materials, components, finished goods and sterilization services. We are dependent on the ability of our suppliers to provide products on a timely basis and on favorable pricing terms. The loss of certain principal suppliers or a significant reduction in product availability from principal suppliers would have a material adverse effect on us, at least in the near term. We believe that our relationships with our suppliers are satisfactory.
Fair Value Measurements	Fair Value Measurements U.S. GAAP defines fair value 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. U.S. GAAP requires an entity to maximize the use of observable inputs, where available, and minimize the use of unobservable inputs when measuring fair value. The Company has certain financial assets and liabilities that are measured at fair value on a recurring basis, certain nonfinancial assets that may be measured at fair value on a nonrecurring basis. The fair value disclosures of these assets and liabilities are based on a three-level hierarchy, which is defined as follows: Level 1 Quoted prices in active markets for identical assets or liabilities that the entity can access at the measurement date. Level 2 Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. Our assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment and considers factors specific to the asset or liability.
Derivative Instruments and Hedging	Derivative Instruments and Hedging Derivative instruments, namely our foreign exchange forward contracts, are recognized on the balance sheet at fair value at the balance sheet date. Changes in the fair value of derivatives that are designated and highly effective as cash flow hedges are deferred in accumulated other comprehensive income (loss) and subsequently recognized in cost of revenues in the same period the hedged items are recognized. The ineffective portion of derivative instruments designated as cash flow hedges are recorded in other income (expense), net. If the underlying forecasted transaction does not occur, or it becomes probable that it will not occur, the gains and losses on the related derivative instrument are recognized in earnings and any related gains and losses recorded in other comprehensive income (loss) are reclassified into earnings. We operate manufacturing and service facilities in Mexico, Germany, and Italy and we purchase materials and pay our employees at those facilities in pesos and euros, and as such, we are potentially exposed to adverse as well as beneficial movements in currency exchange rates. We enter into foreign exchange forward contracts to minimize the impact of currency exchange rate fluctuations on these peso and euro denominated expenses. These contracts have durations of up to twelve months and are designated as cash flow hedges. The counterparties to these foreign exchange forward contracts are creditworthy financial institutions; therefore, we do not consider the risk of counterparty nonperformance to be material.
Inventory	Inventory Inventory is stated at the lower of cost, determined using the first-in first-out method (FIFO), or market (net realizable value). We write down the carrying value of inventory for estimated obsolescence when warranted by an amount equal to the difference between the cost of inventory and the estimated market value based on assumptions of future demand and remaining shelf-life. We also review our inventory value to determine if it reflects the lower of cost or market based on factors such as inventory items sold at negative gross margins and purchase commitments.
Property and Equipment and Field Equipment	Property and Equipment and Field Equipment Property and equipment and field equipment are recorded at cost less accumulated depreciation. Depreciation is provided over the estimated useful lives of the related assets using the straight-line method for financial statement purposes. The estimated useful lives of our assets are periodically reviewed for reasonableness. Changes in useful lives are accounted for prospectively. Repairs and maintenance are expensed as incurred. When property and equipment are retired, sold or otherwise disposed of, the asset's carrying amount and related accumulated depreciation are removed from the accounts and any gain or loss is included in operations. When field equipment is sold, the asset's carrying amount and related accumulated depreciation is removed from the accounts and any gain or loss is deferred and recognized in operations on a straight-line basis over the same period as the related revenues. We capitalize certain costs, including internal payroll and external direct project costs, incurred in connection with developing or obtaining software designated for internal use. These costs are included in property and equipment and are amortized over the estimated useful lives of the related software. Construction-in-process is stated at cost, which includes the cost of construction and other direct costs attributable to the construction. No provision for depreciation is made on construction-in-process until such time as the relevant assets are completed and put into use. Construction-in-process at December 31, 2017 and 2016 primarily represents the costs of building, machinery and equipment under installation. Field equipment consists of equipment being utilized under disposable-based rental agreements as well as “service pool” equipment. Service pool equipment is equipment owned and maintained by us that are swapped for equipment that need repairs or maintenance by us while being rented or owned by a customer. We record a provision for any excess, lost or damaged equipment when warranted based on an assessment of the equipment in the service pool. Write-downs for equipment are included in distribution expenses. The estimated useful lives of property and equipment and field equipment are as follows: Estimated Useful Life Buildings 30 years Equipment and tooling 5 to 12 years Leasehold improvements Lesser of the lease term (including any renewal periods if appropriate) or estimated useful life of the asset Computer and office equipment 3 to 5 years Molds 5 to 7 years Furniture 5 to 7 years Field equipment 5 to 7 years
Intangibles and Other Long-Lived Assets	Intangibles and Other Long-Lived Assets Intangible assets are carried at cost less accumulated amortization. For assets with determinable useful lives, amortization is recognized using the straight-line method over the estimated economic lives of the respective intangible assets. Long-lived assets, including intangible assets, are evaluated for recoverability whenever events or circumstances indicate that their carrying value may not be recoverable. Recoverability of long-lived assets is assessed at the lowest level for which discrete cash flows are available and is measured by comparing the asset group’s carrying value to its expected non-discounted future cash flows. If the sum of the expected non-discounted future cash flows is less than the carrying amount of the long-lived assets, an impairment loss is recognized for excess of the carrying amount of the asset group over its fair value. In 2017 , 2016 and 2015 , events and circumstances have indicated that certain long-lived tangible assets in the Services segment may not be recoverable. Therefore, a recoverability test was performed at the center level by comparing the carrying value of each center to its estimated future undiscounted cash flows, within the initial lease term (which is the equivalent to the depreciable life of the centers' most significant asset, its leasehold improvements). As of December 31, 2017 , our expected non-discounted future cash flows for the majority of our centers indicated such carrying amounts were expected to be recovered. We recorded an impairment charge of $ 0.3 million , $ 0.5 million and $ 0.2 million in 2017 , 2016 and 2015 , respectively, in cost of revenues to write-down certain center level assets within our Services segment. Our expected non-discounted future cash flows used in our impairment testing are based upon cash flow projections and, if appropriate, include assumed proceeds upon sale of the asset group at the end of the cash flow period. We believe our procedures for developing cash flow projections, including the estimated sales proceeds, are reasonable and consistent with current market conditions for each of the dates when impairment testing has been performed. Developing cash flow projections requires significant estimates and judgment. Among other things, slower than expected patient ramp or lower than expected reimbursement rates would negatively impact our cash flow projections in the near term. Fair value of the asset group was estimated using a discounted cash flow approach. Estimating fair value requires significant judgment in the selection of the valuation technique and assumptions used in developing cash flow projections, growth rates and discount rates. Our assumptions are based on our best estimates, using appropriate and customary market participant assumptions. Any adverse changes in certain valuation assumptions could result in the need to record additional impairment to write down all or a portion the centers’ remaining asset carrying value. Additionally, as discussed below in Note 2, effective January 1, 2018, we will adopt the new revenue recognition guidance under ASC 606 . In connection with the adoption of ASC 606, we anticipate recording an increase to center net assets within our Services segment. If the increase in center net assets is greater than the excess fair value over the carrying value of net assets an impairment charge would be recognized. We had $13.9 million of long-lived assets at our Services segment at December 31, 2017 . It is reasonably possible that our cash flow projections may change or the carrying value of our net assets many change in the near term resulting in the need to record an impairment charge for at least some portion of these assets. Assets to be disposed of are reported at the lower of the carrying amount or fair value less selling costs.
Goodwill	Goodwill Goodwill represents the excess of the cost of an acquired business over the acquisition value of the related net assets at the date of acquisition. We test goodwill at least annually for impairment during the fourth quarter, or more frequently when events or changes in circumstances indicate that the goodwill might be impaired. This test includes first a qualitative assessment and then, if necessary, a quantitative assessment to determine if the fair value of a reporting unit is less than its carrying amount. Our System One, In-center and Services reporting units contain goodwill of $41.1 million, $0.5 million and $1.1 million, respectively. Factors considered in the qualitative assessment include, but are not limited to, both macroeconomic conditions and entity-specific conditions. For the quantitative assessment, the reporting unit's fair value is estimated using a discounted cash flow or other fair value measurement. During 2017 , 2016 and 2015 we utilized the qualitative assessment to assess the fair value of our System One and In-center reporting units and concluded that it was more likely than not that the fair value of our reporting units was greater than their carrying value. During 2017 , for our Services reporting unit, we utilized the quantitative assessment noting that the fair value of the reporting unit exceeds its carrying value, indicating that goodwill was not impaired. We estimated the fair value of our Services reporting unit using a discounted cash flow approach. Estimating the fair value of our Services reporting unit requires significant judgment in the selection of the valuation technique and assumptions used in cash flow projections, growth rates and discount rates. Our assumptions are based on our best estimates, using appropriate and customary market participant assumptions. Additionally, as discussed in Note 2 below, effective January 1, 2018, we adopted the new revenue recognition guidance under ASC 606 that we anticipate will result in an increase to our Services center reporting units net asset value. If the increase in net assets is greater than the excess fair value over the carrying value of net assets, an impairment charge would be recognized. Developing cash flow projections involves significant judgment with respect to patient ramp and reimbursement rates, operating income, capital expenditures and changes in working capital. Reductions in our cash flow projections due to slower than expected patient ramp or lower than expected reimbursement rates, among other things, or adverse changes in certain valuation assumptions or changes in the reporting units net assets resulting from the adoption of ASC 606 could result in a goodwill impairment charge of up to $ 1.1 million in the future.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation expense is estimated as of the grant date based on the fair value of the award. We use the Black-Scholes option pricing model to estimate the fair value of stock options and quoted market prices of our common stock to estimate fair value of restricted stock. The expected term is estimated based on the contractual term of each grant and takes into account the historical experience and relevant factors concerning expected exercise and termination behavior of participants. The risk free interest rate for each grant is equal to the U.S. Treasury rate in effect at the time of grant for instruments with an expected life similar to the expected term. The stock volatility assumption is based solely on our historical volatility over the expected term of the award. The dividend yield of zero is based upon the fact that we have not historically granted cash dividends, and do not expect to issue dividends in the foreseeable future. We recognize stock-based compensation expense over the requisite service period, which equals the vesting period, net of forfeitures. Forfeiture rates are estimated based on historical pre-vesting forfeiture history and are updated on a quarterly basis to reflect actual forfeitures of unvested awards and other known events. For awards that vest based on employment, we recognize the associated compensation expense on a straight-line basis. For performance based awards, we recognize expense using the graded vesting methodology based on the number of shares expected to vest. Compensation expense associated with these performance based awards is adjusted quarterly to reflect subsequent changes in the estimated outcome of performance-related conditions until the date the results are determined.
Warranty Costs	Warranty Costs We accrue estimated costs that we may incur under our product warranty programs at the time the product revenue is recognized, based on contractual rights and historical experience. Warranty expense is included in cost of revenues in the consolidated statements of comprehensive loss.
Distribution Expenses	Distribution Expenses Distribution expenses are charged to operations as incurred and consist of costs incurred in shipping product to and from customers and the cost of any equipment lost or damaged in the distribution process. Shipping and handling costs billed to customers are included in revenues.
Research and Development Costs	Research and Development Costs Research and development costs are charged to operations as incurred.
Income Taxes	Income Taxes We record the tax effect of transactions when such transactions are recorded in our consolidated statement of comprehensive loss. We record a deferred tax asset or liability based on the difference between the financial statement and tax basis of assets and liabilities, as measured by the enacted tax rates. Our provision for income taxes represents the amount of taxes currently payable, if any, plus the change in the amount of net deferred tax assets or liabilities. A valuation allowance is provided against net deferred tax assets if recoverability is uncertain on a more likely than not basis. We periodically assess our exposures related to our provisions for income taxes and accrue for contingencies that may result in potential tax obligations. For those positions where it is more likely than not that a tax benefit will be sustained, we record the largest amount of tax benefit with a greater than 50 percent likelihood of being realized upon ultimate settlement with a taxing authority that has full knowledge of all relevant information. For those income tax positions where it is not more likely than not that a tax benefit will be sustained, no tax benefit is recognized in the financial statements. We recognize interest and penalties for uncertain tax positions in income tax expense. We conduct business globally and file income tax returns in the U.S. federal jurisdiction, various states and foreign jurisdictions. We estimate our income taxes in each of the jurisdictions in which we operate. We have accumulated significant losses since our inception in 1998. The utilization of these losses may be limited in future years based on the profitability of certain entities.
Subsequent Events	Subsequent Events Events occurring subsequent to December 31, 2017 have been evaluated for potential recognition or disclosure in the consolidated financial statements.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Recently Implemented Accounting Pronouncements In July 2015, the Financial Accounting Standards Board (FASB) issued ASU No. 2015-11, Inventory (Topic 330): "Simplifying the Measurement of Inventory." The update requires that an entity should measure in scope inventory at the lower of cost and net realizable value. Net realizable value is the estimated selling prices in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation. The amendments were effective for us beginning January 1, 2017. The adoption of this update did not have a material impact on our financial statements. In March 2016, the FASB issued ASU No. 2016-09: “Improvements to Employee Share-Based Payment Accounting,” which simplifies several aspects of the accounting for employee share-based payment transactions for both public and nonpublic entities, including the accounting for income taxes, forfeitures, and statutory tax withholding requirements, as well as classification in the statement of cash flows. The new guidance was effective for us beginning January 1, 2017. We have elected to continue to estimate forfeiture rates. This new standard impacts our income tax footnote disclosures. We have tax effected federal net operating losses of $18.0 million and state net operating losses of $1.6 million that are attributable to excess tax deductions related to stock-based compensation from prior years. Upon adoption, the cumulative excess tax deductions related to stock-based compensation that were previously unrecognized are being recognized as a deferred tax asset and are fully offset by a valuation allowance. Other than this change in our income tax footnote disclosures, the adoption does not have a material impact on our financial statements. In January 2017, the FASB issued ASU No. 2017-04: "Intangibles - Goodwill and Other Topics (Topic 350): Simplifying the Test for Goodwill Impairment". The purpose of this update is to reduce the cost and complexity of evaluating goodwill for impairment. It eliminates the need for entities to calculate the impaired fair value of goodwill by assigning the fair value of a reporting unit to all of its assets and liabilities as if that reporting unit had been acquired in a business combination. Under this update, an entity will perform its goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An impairment charge is recognized for the amount by which the carrying value exceeds the reporting unit's fair value. We elected to early adopt this update on a prospective basis for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The adoption of this update did not have a material impact on our financial statements. In May 2017, the FASB issued ASU No. 2017-09: "Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting". The purpose of this update is to reduce the diversity in practice and result in fewer changes to the terms of an award being accounted for as modifications. It will allow companies to make non-substantive changes to their share-based payment awards, without accounting for them as modifications. It does not change the accounting for modifications. Under this update, an entity will apply the modification accounting guidance only if the value (or calculated value or intrinsic value, if those measurement methods are used), vesting conditions or classification of the award as an equity or liability instrument changes. This update also clarifies that a modification to an award could be significant and therefore require disclosure, even if modification accounting is not required. The new guidance will be applied prospectively to awards modified on or after the adoption date. We elected to early adopt this update in the second quarter of 2017. The adoption of this update did not have a material impact on our financial statements. Recent Accounting Pronouncements Not Yet Adopted In May 201 4, the FASB issued ASU No. 2014-9: “Revenue from Contracts with Customers” (ASC 606). The standard provides that revenue should be recognized when an entity transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In addition, the standard requires disclosure of the nature, amount, timing and uncertainty of revenues and cash flow arising from contracts with customers. The FASB has issued several amendments and updates to the new revenue standard, including how an entity should identify performance obligations. As amended, the new guidance is effective for us beginning January 1, 2018. We have elected to adopt ASC 606 using the modified retrospective method approach as of January 1, 2018. This approach was applied to all contracts not completed as of January 1, 2018. The adoption of ASC 606 is expected to have a material effect on our consolidated financial statements primarily relating to the timing of revenue recognition for our Services segment along with enhanced footnote disclosures related to customer contracts. We are working to complete our evaluation of the impact of the standard on significant contracts from each of our business segments. We are evaluating the impact the standard will have on our disclosures along with any related indirect effects of adoption and are implementing changes to our current policies and practices, accounting systems and internal controls over financial reporting to address the requirements of the standard. The qualitative assessment of the standard provided below are estimates of the expected effects of the adoption of ASC 606. This represents our best estimate of the effects of adopting ASC 606 at the time of the preparation of this Annual Report on Form 10-K. The actual impact of ASC 606 is subject to change from these estimates and such change may be significant, pending the completion of our assessment in the first quarter of 2018. System One Segment Revenue . We expect that the deliverables under the current guidance will be consistent with performance obligations identified under ASC 606. Under ASC 606, we will continue to allocate the transaction price between the elements and performance obligations within the contract. Revenue recognition for the performance obligations accounted for under ASC 606 is expected to be consistent with current guidance given the transfer of control of the promised goods or services follows the same pattern. As such, we do not expect the adoption of ASC 606 will result in a material impact to revenue recognition. In-Center Segment Revenue We expect that the deliverables under the current guidance will be consistent with performance obligations identified under ASC 606. Under the new guidance, the variable fee paid by the distributor will be estimated and recognized when the Company satisfies its performance obligation (generally upon delivery to the distributor) to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized to date will not occur.This will result in a similar revenue recognition model to current guidance and as such, we do not expect the adoption of ASC 606 will result in a material impact to revenue recognition. Services Segment Revenue . We expect that the deliverables under the current guidance will be consistent with performance obligations identified under ASC 606. The adoption of ASC 606, will result in a change to the timing of revenue recognition for this segment as the standard requires revenues to be estimated and recognized upon transfer of the promised goods and services. We are working to quantify the January 1, 2018 impact to accumulated deficit and accounts receivable. Costs to Obtain or Fulfill a Contract . Commissions are paid to internal sales representatives as compensation for obtaining sales on a monthly or quarterly basis. Due to the structure of the commission’s plans, we have concluded the period of benefit for any commission payment is less than a year. As such we expect to conclude that we will apply the practical expedient pursuant to ASC 340-40 which permits an entity to immediately expense contract acquisition costs when the assets that would have resulted from capitalizing those costs would have been amortized in one year or less. Therefore, we do not expect the adoption of this aspect of ASC 606 to have a material impact on our financial statements. In January 2016, the FASB issued ASU No. 2016-01: “Financial Instruments-Overall: Recognition and Measurement of Financial Assets and Financial Liabilities” which impacts the recognition, measurement, presentation and disclosure of financial assets and financial liabilities. Among other things, the new standard generally requires all equity investments (except those accounted for under the equity method and those that result in consolidation of the investee) be measured at fair value through earnings. The new guidance is effective for us beginning January 1, 2018. The adoption of this standard is not expected to have a material impact on our financial statements. In January 2017, the FASB issued ASU No. 2017-01: "Business Combinations (Topic 805): Clarifying the Definition of a Business" which changes the definition of a business to assist entities with evaluating when a set of transferred assets and activities is a business. The update is effective for us beginning January 1, 2018. The adoption of this update is not expected to have a material impact on our financial statements. In February 2016, the FASB issued ASU No. 2016-02: "Accounting for Leases" which amends the existing accounting standards for leases. The new standard requires lessees to record a right-of-use asset and a corresponding lease liability on the balance sheet for all leases with terms longer than twelve months. For lessees, leases will continue to be classified as either operating or financing in the income statement. This ASU is required to be applied with a modified retrospective approach and requires application of the new standard at the beginning of the earliest comparative period presented. The new guidance is effective for us beginning January 1, 2019 and early adoption is permitted. We intend to adopt this standard as of January 1, 2019. We are currently evaluating the potential impact this standard will have on our financial statements. In August 2017, the FASB issued ASU 2017-12: "Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities" which amends the hedge accounting recognition and presentation requirements. The update is intended to more closely align hedge accounting with companies’ risk management strategies, simplify the application of hedge accounting and increase transparency as to the scope and results of hedge programs. The update is effective for us beginning January 1, 2019, with early adoption permitted. We are currently evaluating the potential impact this update will have on our financial statements.
Net Loss Per Share	Basic net loss per share is computed by dividing loss attributable to NxStage Medical, Inc. common stockholders (the numerator) by the weighted-average number of common shares outstanding (the denominator) for the period. The computation of diluted loss per share is similar to basic loss per share, except that the denominator is increased to include the number of additional common shares that would have been outstanding if the potentially dilutive common shares had been issued.
Legal Contingencies	Legal Contingencies From time to time, during the ordinary course of operations, we are party to litigation and arbitration and are subject to investigations relating to various aspects of our business. We regularly analyze current information about such claims for probable losses and provide accruals for such matters, including the estimated legal expenses and consulting services in connection with these matters, as appropriate. We utilize our internal legal department as well as external resources for these assessments. In making the decision regarding the need for loss accrual, we consider the degree of probability of an unfavorable outcome and our ability to make a reasonable estimate of the amount of loss. In management's opinion, we are not currently involved in any legal proceedings which, individually or in the aggregate, are reasonably likely to have a material adverse effect on our financial condition or results of operations.
Noncontrolling Interests	Noncontrolling interests represent the third-party equity ownership interests in consolidated entities for which we have effective control, including variable interest entities (VIE) for which we are deemed the primary beneficiary. We assess the terms of our investment interests to determine if any of our investees meet the definition of a VIE. For any VIEs, we perform an analysis to determine whether our variable interests give us a controlling financial interest in a VIE. The analysis identifies the primary beneficiary of a VIE as the enterprise that has both 1) the power to direct activities of a VIE that most significantly impact the entity’s economic performance and 2) the obligation to absorb losses of the entity or the right to receive benefits from the entity.
Fair Value Measurements	We measure the fair value of our foreign exchange forward contracts classified as derivative instruments using an income approach, based on prevailing market forward rates less the contract rate multiplied by the notional amount. The product of this calculation is then adjusted for counterparty risk.

Summary of Significant Accoun28

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Allowance for Doubtful Accounts	Activity related to allowance for doubtful accounts consisted of the following (in thousands): Year Ended Balance at Beginning of Year Provision Write-offs Balance at End of Year December 31, 2017 $ 535 $ 471 $ (191 ) $ 815 December 31, 2016 $ 417 $ 179 $ (61 ) $ 535 December 31, 2015 $ 425 $ 20 $ (28 ) $ 417
Estimated Useful Lives of Property and Equipment and Field Equipment	The estimated useful lives of property and equipment and field equipment are as follows: Estimated Useful Life Buildings 30 years Equipment and tooling 5 to 12 years Leasehold improvements Lesser of the lease term (including any renewal periods if appropriate) or estimated useful life of the asset Computer and office equipment 3 to 5 years Molds 5 to 7 years Furniture 5 to 7 years Field equipment 5 to 7 years
Rollforward of Warranty Accrual	The following is a rollforward of our warranty accrual (in thousands): Year Ended Balance at Beginning of Year Provision Usage Balance at End of Year December 31, 2017 $ 280 $ 445 $ (432 ) $ 293 December 31, 2016 $ 389 $ 457 $ (566 ) $ 280 December 31, 2015 $ 287 $ 526 $ (424 ) $ 389

Inventory (Tables)

Inventory (Tables)	12 Months Ended
	Dec. 31, 2017
Inventory Disclosure [Abstract]
Components of Inventory	The components of inventory are as follows (in thousands): December 31, 2017 2016 Purchased components $ 14,947 $ 14,967 Work in process 13,433 13,939 Finished goods 20,832 17,939 $ 49,212 $ 46,845

Property and Equipment, Field30

Property and Equipment, Field Equipment and Deferred Cost of Revenues (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Summary of Components of Property and Equipment, Net	The components of property and equipment, net are as follows (in thousands): December 31, 2017 2016 Equipment and tooling $ 44,823 $ 39,921 Leasehold improvements 34,812 35,146 Computer and office equipment 8,593 10,035 Molds 7,573 6,805 Furniture 3,612 3,561 Building 9,414 8,057 Land 1,091 956 Construction-in-process 7,138 4,237 117,056 108,718 Less accumulated depreciation (56,794 ) (47,157 ) Property and equipment, net $ 60,262 $ 61,561
Components of Assets Subject to Capital Leases	Our property and equipment includes the following amounts for assets subject to capital leases (amounts in thousands): December 31, 2017 2016 Manufacturing facility in Germany $ 24,135 $ 21,007 Other assets subject to capital lease 4,453 3,024 Less accumulated depreciation (8,979 ) (6,402 ) Assets subject to capital leases, net $ 19,609 $ 17,629
Components of Field Equipment, Net	The components of field equipment, net are as follows (in thousands): December 31, 2017 2016 Field equipment $ 75,823 $ 70,743 Less accumulated depreciation (51,559 ) (48,434 ) Field equipment, net $ 24,264 $ 22,309
Components of Deferred Costs of Revenues	The components of deferred costs of revenues, net are as follows (in thousands): December 31, 2017 2016 Deferred costs of revenues $ 137,734 $ 126,375 Less accumulated amortization (106,324 ) (93,210 ) Deferred costs of revenues, net $ 31,410 $ 33,165

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Summary of Intangible Assets	The components of intangible assets, net are as follows (in thousands): December 31, 2017 December 31, 2016 Estimated Cost Accumulated Amortization Cost Accumulated Amortization Useful Life Bloodline, needle and other patented and unpatented technology $ 6,200 $ (6,200 ) $ 6,200 $ (6,200 ) 8 years Trade names 2,300 (1,684 ) 2,300 (1,520 ) 14 years Customer relationships 26,151 (19,107 ) 26,138 (17,230 ) 10/14 years Intangible assets, net $ 34,651 $ (26,991 ) $ 34,638 $ (24,950 )
Estimated Future Aggregated Amortization Expense for Intangible Assets	The estimated future aggregated amortization expense for intangible assets as of December 31, 2017 is as follows (in thousands): 2018 $ 2,036 2019 2,036 2020 2,036 2021 1,552 $ 7,660

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Schedule of Anti-dilutive Net Loss Per Share	The following potential common stock equivalents, as calculated using the treasury stock method, were not included in the computation of diluted net loss per share as their effect would have been anti-dilutive due to the net loss incurred (in thousands): Years Ended December 31, 2017 2016 2015 Options to purchase common stock 1,100 785 732 Unvested restricted stock 224 361 350 Total 1,324 1,146 1,082

Accrued Expenses, Other Curre33

Accrued Expenses, Other Current Liabilities, and Other Long Term Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Components of Accrued Expenses	The components of accrued expenses are as follows (in thousands): December 31, 2017 2016 Payroll, compensation and related benefits $ 13,195 $ 14,086 Distribution expenses 4,914 4,804 General and administrative expenses 1,670 4,415 Other 8,206 7,680 Total $ 27,985 $ 30,985
Components of Other Current liabilities	The components of other current liabilities are as follows (in thousands): December 31, 2017 2016 Capital lease obligations $ 2,131 $ 1,840 Deferred revenue, current portion 1,473 1,035 Other 955 895 Total $ 4,559 $ 3,770
Schedule of Other Long-term Liabilities	The components of other long term liabilities are as follows (in thousands): December 31, 2017 2016 Capital lease obligations $ 11,589 $ 9,991 Lease incentive obligations 2,652 3,059 Benefit plan obligations 2,060 1,678 Other 1,523 840 Total $ 17,824 $ 15,568

Debt and Capital Lease Obliga34

Debt and Capital Lease Obligations (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Future Minimum Payments under Capital Leases	Approximate future minimum payments under our capital leases as of December 31, 2017 are as follows (in thousands): 2018 $ 1,674 2019 1,733 2020 1,792 2021 1,932 2022 1,820 Thereafter (1) 7,539 Total minimum lease payments 16,490 Less: Amount representing interest (2,770 ) Present value of future minimum lease payments $ 13,720 _________________________________ (1) Amount includes $6.9 million representing the estimated residual value of the manufacturing facility in Germany at the end of the estimated lease term, which only becomes due and payable at Asahi's option if we terminate our agreement with Asahi.

Business Segment and Geograph35

Business Segment and Geographic Information (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Summary of Operating Performance of Reportable Segments	The following summarizes the operating performance of our reportable segments (in thousands): System One In-Center Other Services Intersegment Elimination Total Year Ended December 31, 2017 Revenues from external customers $ 301,299 $ 61,307 $ 11,796 $ 19,539 $ — $ 393,941 Intersegment Revenues 5,062 — — — (5,062 ) — Revenues 306,361 61,307 11,796 19,539 (5,062 ) 393,941 Segment profit (loss) 82,585 8,070 (80,804 ) (23,702 ) — (13,851 ) Depreciation and amortization 22,166 2,121 4,349 5,217 (99 ) 33,754 Segment assets 134,825 25,225 146,737 19,712 (870 ) 325,629 Year Ended December 31, 2016 Revenues from external customers $ 276,393 $ 63,038 $ 12,166 $ 14,781 $ — $ 366,378 Intersegment Revenues 7,530 — — — (7,530 ) — Revenues 283,923 63,038 12,166 14,781 (7,530 ) 366,378 Segment profit (loss) 74,912 10,092 (62,309 ) (26,233 ) (747 ) (4,285 ) Depreciation and amortization 23,671 2,003 4,427 4,781 (2,245 ) 32,637 Segment assets 135,038 21,246 138,273 23,620 (970 ) 317,207 Year Ended December 31, 2015 Revenues from external customers $ 244,641 $ 74,768 $ 10,302 $ 6,412 $ — $ 336,123 Intersegment Revenues 3,134 — — — (3,134 ) — Revenues 247,775 74,768 10,302 6,412 (3,134 ) 336,123 Segment profit (loss) 59,748 12,395 (62,946 ) (23,826 ) — (14,629 ) Depreciation and amortization 20,554 1,835 5,004 3,322 — 30,715 Segment assets 120,253 24,232 142,842 19,547 — 306,874
Reconciliation of Total Segment Assets to Total Assets	The following table presents a reconciliation of the total segment assets to total assets (in thousands): December 31, 2017 2016 Total segment assets $ 179,762 $ 179,904 Intersegment elimination (870 ) (970 ) Corporate assets: Cash and cash equivalents 64,927 59,632 Accounts Receivable, net 949 632 Inventory 305 — Property and equipment, net 16,628 16,600 Intangible assets, net 7,660 9,688 Goodwill 42,748 42,648 Prepaid and other assets 13,520 9,073 Total assets $ 325,629 $ 317,207
Schedule of Total Long-Lived Tangible Assets by Geographic Area	The following table presents total long-lived tangible assets by geographic area (in thousands): December 31, 2017 2016 2015 United States $ 42,610 $ 46,724 $ 46,551 Mexico 16,790 13,431 14,233 Other Americas 1,630 571 825 Total Americas 61,030 60,726 61,609 Germany 18,270 17,574 19,053 Other Europe 5,226 5,754 6,793 Total Europe 23,496 23,328 25,846 Total $ 84,526 $ 84,054 $ 87,455
Summary of Number of Customers Who Individually Make Up Greater than 10% of Total Revenues	The following table summarizes the number of customers who individually make up greater than ten percent of total revenues: Years Ended December 31, 2017 2016 2015 DaVita 20 % 20 % 20 % Fresenius 20 % 18 % 17 %

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Future Minimum Rental Payments Under Operating Leases	The future minimum rental payments as of December 31, 2017 under our operating leases are as follows (in thousands): 2018 $ 5,463 2019 4,811 2020 4,297 2021 3,694 2022 3,174 Thereafter 2,708 $ 24,147

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Summary of Income (Loss) Before Income Taxes by Geography	The following is a summary of income (loss) before income taxes by geography (in thousands): Years Ended December 31, 2017 2016 2015 U.S. $ (19,314 ) $ (9,265 ) $ (17,672 ) Foreign 3,844 3,050 2,489 Total $ (15,470 ) $ (6,215 ) $ (15,183 )
Components of Provision for (Benefit from) Income Taxes	The components of the provision for income taxes are as follows (in thousands): Years Ended December 31, 2017 2016 2015 Current: U.S. - Federal $ (1,269 ) $ — $ — U.S. - State 96 73 86 Foreign 1,540 1,200 1,225 Total Current 367 1,273 1,311 Deferred: Foreign (512 ) (171 ) (234 ) Total Deferred (512 ) (171 ) (234 ) Total Provision $ (145 ) $ 1,102 $ 1,077
Reconciliation of U.S. Federal Statutory Tax Rate to Effective Tax Rate	A reconciliation of the U.S. federal statutory tax rate to the effective tax rate is as follows: Years Ended December 31, 2017 2016 2015 Federal statutory rate 34.0 % 34.0 % 34.0 % Stock compensation 25.7 % (1.5 )% (2.5 )% State income tax, net of federal tax benefit 2.3 % (2.3 )% (2.8 )% U.S. research credits 6.7 % 18.9 % (0.3 )% Foreign income inclusion in the U.S. (4.7 )% (10.4 )% (5.0 )% Valuation allowance 149.4 % (47.4 )% (25.8 )% Change in tax reserves (1.4 )% (0.5 )% (0.5 )% Minority Interest (1.6 )% (15.9 )% (0.9 )% Tax Reform impact (344.6 )% — % — % Intraperiod tax allocation 8.2 % — % — % ASU 2016-09 126.7 % — % — % Other, net 0.2 % 7.4 % (3.3 )% Effective tax rate 0.9 % (17.7 )% (7.1 )%
Deferred Tax Assets (Liabilities)	Deferred tax assets (liabilities) are made up of the following (in thousands): December 31, 2017 2016 Deferred tax assets: Net operating loss carryforwards $ 92,315 $ 115,151 Tax credits 12,706 11,180 Stock-based compensation 4,922 7,339 Capitalized research and development 1,126 2,167 Financing liabilities 5,531 5,161 Other 7,613 8,349 Total deferred tax assets 124,213 149,347 Deferred tax liabilities: Fixed assets (5,485 ) (5,754 ) Intangible assets (1,902 ) (3,606 ) Other (222 ) (187 ) Total deferred tax liabilities (7,609 ) (9,547 ) Net deferred tax assets before valuation allowance 116,604 139,800 Less valuation allowance (115,035 ) (138,795 ) Net deferred tax assets $ 1,569 $ 1,005
Changes in Unrecognized Tax Benefits	The below table details the changes in unrecognized tax benefits, which if recognized would favorably impact our effective tax rate (in thousands): Years Ended December 31, 2017 2016 2015 Balance at beginning of the year $ 517 $ 379 $ 347 Increase in unrecognized tax benefits as a result of tax positions taken during the current year 275 89 66 Increase (decrease) in unrecognized tax benefits as a result of tax positions taken during a prior year 50 115 (34 ) Reductions due to lapse of applicable statute of limitations (78 ) (66 ) — Balance at end of year $ 764 $ 517 $ 379

Stock Plans and Stock-Based C38

Stock Plans and Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Status of Stock Options Granted Under All Plans	A summary of the status of stock options granted under all of our plans at December 31, 2017 , and changes during the year then ended, is as follows: Stock Options Shares Weighted Average Exercise Price Aggregate Intrinsic Value Average Remaining Contractual Life (In thousands) (In years) Outstanding at beginning of year 4,656,405 $ 15.02 Granted 675,358 $ 26.87 Exercised (1,130,939 ) $ 13.79 Forfeited or expired (83,627 ) $ 20.50 Outstanding at end of year 4,117,197 $ 17.19 $ 30,825 6.75 Fully vested and exercisable 2,684,405 $ 15.90 $ 22,730 6.05 Fully vested, exercisable and expected to vest 4,002,574 $ 17.12 $ 30,177 6.71
Estimated Fair Value of Options at Date of Grant	The fair value of options at date of grant was estimated using the Black-Scholes option-pricing model with the following assumptions: Years Ended December 31, 2017 2016 2015 Expected life (in years) 5.00 to 6.50 5.00 to 9.92 4.80 to 10.00 Risk-free interest rate 1.79% to 2.13% 1.20% to 2.45% 1.34% to 2.27% Expected stock price volatility 36.8% to 38.8% 38% to 43.05% 38% to 42.52% Expected dividend yield — — —
Summary of Status of Unvested Restricted Stock Units	The following table summarizes the status of the unvested restricted stock: Shares Weighted Average Grant-date Fair Value Aggregate Intrinsic Value Weighted Average Remaining Contractual Life (In thousands) (In years) Unvested at December 31, 2016 1,143,800 $ 15.57 Granted 407,279 $ 25.10 Vested (339,496 ) $ 14.24 Forfeited (499,253 ) $ 16.26 Unvested at December 31, 2017 712,330 $ 21.17 $ 17,260 2.14
Valuation Assumptions for ESPP	The fair value of the employees' stock purchase rights was estimated using the Black-Scholes option-pricing model with the following assumptions: Years Ended December 31, 2017 2016 2015 Expected life (in months) 6 6 6 Risk-free interest rate 0.65% to 1.13% 0.37% to 0.49% 0.11% to 0.13% Expected stock price volatility 36.4% to 39.2% 39.6% to 48.2% 18.4% to 22.4% Expected dividend yield — — —
Summary of Stock-Based Compensation Expense in Consolidated Statements of Comprehensive Loss	The following table presents stock-based compensation expense included in the consolidated statements of comprehensive loss (in thousands): Years Ended December 31, 2017 2016 2015 Cost of revenues $ 1,201 $ 1,371 $ 1,068 Selling and marketing 3,933 3,304 4,458 Research and development 1,539 1,536 1,979 General and administrative 4,864 3,906 5,093 Total stock-based compensation expense $ 11,537 $ 10,117 $ 12,598

Noncontrolling Interests (Table

Noncontrolling Interests (Tables)	12 Months Ended
	Dec. 31, 2017
Noncontrolling Interest [Abstract]
Changes In Noncontrolling Interest Table	The following table sets forth the changes in noncontrolling interest not subject to put provisions for the periods indicated (in thousands): Years Ended December 31, 2017 2016 2015 Balance at beginning of period $ 625 $ 1,694 $ 1,088 Capital contributions by noncontrolling interest — 630 1,316 Sales of noncontrolling interests — 679 208 Add: Accretion to redemption value of noncontrolling interests 481 — — Reclassification of noncontrolling interest subject to put provision 322 — — Net loss attributable to noncontrolling interest in consolidated subsidiary (1,440 ) (2,378 ) (918 ) Balance at end of period $ (12 ) $ 625 $ 1,694

Derivative Instruments and He40

Derivative Instruments and Hedging (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Effect of Contracts Designated as Cash Flow Hedges on Consolidated Financial Statements	The following table presents the effect of these contracts designated as cash flow hedges on our consolidated financial statements (in thousands): Gain (Loss) Recognized in OCI (Effective Portion) Gain (Loss) Reclassified from OCI into Income (Effective Portion) Classification within the Condensed Consolidated Statement of Comprehensive Loss Year Ended December 31, 2017 Foreign exchange forward contracts $ 3,433 $ 1,163 Cost of revenues Year Ended December 31, 2016 Foreign exchange forward contracts $ (2,712 ) $ (1,910 ) Cost of revenues Year Ended December 31, 2015 Foreign exchange forward contracts $ (2,140 ) $ (1,745 ) Cost of revenues

Accumulated Other Comprehensi41

Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Summary of Additional Information on Accumulated Other Comprehensive (Loss) Income	The following additional information is provided with respect to the accumulated other comprehensive (loss) income as presented on the condensed consolidated balance sheets (in thousands): Unrealized gain (loss) on derivative instruments Other (2) Total Balance, net of tax, as of December 31, 2014 $ (1,088 ) $ (1,104 ) $ (2,192 ) Other comprehensive income before reclassifications (2,140 ) (1,444 ) (3,584 ) Loss reclassified to earnings (1) 1,745 — 1,745 Total other comprehensive income (loss) (395 ) (1,444 ) (1,839 ) Balance, net of tax, as of December 31, 2015 $ (1,483 ) $ (2,548 ) $ (4,031 ) Other comprehensive income before reclassifications (2,712 ) (1,268 ) (3,980 ) Gain reclassified to earnings (1) 1,910 — 1,910 Total other comprehensive income (loss) (802 ) (1,268 ) (2,070 ) Balance, net of tax, as of December 31, 2016 $ (2,285 ) $ (3,816 ) $ (6,101 ) Other comprehensive income before reclassifications, net of $1,269 tax during 2017 2,164 1,427 3,591 Gain/Loss reclassified to earnings (1) (1,163 ) — (1,163 ) Total other comprehensive income (loss) 1,001 1,427 2,428 Balance, net of tax, as of December 31, 2017 $ (1,284 ) $ (2,389 ) $ (3,673 ) (1) Reclassifications of gains (losses) on derivative instruments are included in cost of revenues on the consolidated statement of comprehensive loss. See Note 16, Derivative Instruments and Hedging for further information. (2) Other includes cumulative translation adjustments and, to a lesser extent, pension benefits.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis	The following tables present assets and liabilities measured at fair value on a recurring basis and their level within the value hierarchy (in thousands): December 31, 2017 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Fair Value Assets Money market funds (1) $ 35,020 $ — $ — $ 35,020 Foreign exchange forward contracts (2) — 690 — 690 Liabilities Foreign exchange forward contracts (2) $ — $ 661 $ — $ 661 December 31, 2016 Quoted Prices in Active Markets for Identical Assets Significant Other Observable Inputs Significant Unobservable Inputs Total Fair Value Assets Money market funds (1) $ 34,804 $ — $ — $ 34,804 Foreign exchange forward contracts (2) — — — — Liabilities Foreign exchange forward contracts (2) $ — $ 1,771 $ — $ 1,771 (1) Money market funds are included within cash and cash equivalents. (2) Foreign exchange forward contracts are included within prepaid expenses and other current assets or accrued expenses depending on the gain (loss) position.

Supplemental Cash Flow Inform43

Supplemental Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Summary of Supplemental Cash Flow Information	The following additional information is provided with respect to the consolidated statements of cash flows (in thousands): Years Ended December 31, 2017 2016 2015 Supplemental Disclosures: Cash paid for interest $ 638 $ 639 $ 703 Cash paid for taxes 1,258 983 919 Noncash Investing and Financing Activities: Transfers from inventory to field equipment $ 19,257 $ 20,920 $ 16,675 Transfers from field equipment to deferred cost of revenues 11,026 13,400 11,638 Payment of corporate bonus plan in common stock — — 1,103 Market value of shares received in payment for exercise of stock options 3,100 2,320 875 Construction-in-process financed by construction liability 142 187 1,332 Redemption of noncontrolling interest 481 — — Property and equipment acquired under capital lease — 127 354 Acquisition of business — — 513 Increase in deferred revenues related to the new manufacturing facility in Germany — — 663 Capital contributions by noncontrolling interest — 54 325

Quarterly Financial Data (Una44

Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data (Unaudited)	The following table sets forth selected quarterly information (unaudited) (in thousands, except per share data): Three Months Ended March 31, June 30, September 30, December 31, Revenues $ 96,829 $ 96,216 $ 97,295 $ 103,601 Gross profit 41,190 41,166 40,607 45,325 Loss from operations (1,681 ) (2,056 ) (8,283 ) (1,831 ) Net loss (1,541 ) (2,579 ) (8,894 ) (2,311 ) Net loss attributable to stockholders of NxStage Medical, Inc. (1,189 ) (2,089 ) (8,445 ) (2,269 ) Net loss attributable to common stockholders (1,189 ) (2,089 ) (8,926 ) (2,269 ) Net loss per share, basic and diluted $ (0.02 ) $ (0.03 ) $ (0.14 ) $ (0.03 ) Three Months Ended March 31, June 30, September 30, December 31, Revenues $ 89,207 $ 92,207 $ 91,951 $ 93,013 Gross profit 36,517 38,423 39,181 37,864 Loss from operations (975 ) (1,180 ) 24 (2,154 ) Net loss (1,783 ) (2,225 ) (890 ) (2,419 ) Net loss attributable to stockholders of NxStage Medical, Inc. (1,276 ) (1,732 ) (166 ) (1,597 ) Net loss attributable to common stockholders (1,276 ) (1,732 ) (166 ) (1,597 ) Net loss per share, basic and diluted $ (0.02 ) $ (0.03 ) $ (0.00 ) $ (0.02 )

Nature of Operations, Propose45

Nature of Operations, Proposed Merger, Basis of Presentation and Principles of Consolidation - Additional Information (Details) $ / shares in Units, $ in Millions	Oct. 27, 2017USD ($)$ / shares	Oct. 18, 2017	Dec. 31, 2017country
Accounting Policies [Abstract]
Number of countries in which entity operates | country			21
Fresenius Medical Care Holdings, Inc.
Business Acquisition [Line Items]
Share price | $ / shares	$ 30
Waiting period term		30 days
Extension term	180 days
Termination fee, fee paid to acquiree	$ 100
Termination fee, fee paid to acquirer	$ 60
Period to not enter into alternative acquisition after termination	12 months

Summary of Significant Accoun46

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Line Items]
Intangible assets, net		$ 7,660	$ 9,688
Goodwill		$ 42,748	$ 42,648
Expected dividend yield		0.00%
Percentage of tax benefit realized upon ultimate settlement with taxing authority		50.00%
Long-Lived Assets of Several Centers
Accounting Policies [Line Items]
Intangible assets, net		$ 13,900
Customer Concentration Risk | Accounts Receivable
Accounting Policies [Line Items]
Percentage of accounts receivable		10.00%
Major Customer One | Customer Concentration Risk | Accounts Receivable
Accounting Policies [Line Items]
Percentage of accounts receivable			12.00%
Major Customer Two | Customer Concentration Risk | Accounts Receivable
Accounting Policies [Line Items]
Percentage of accounts receivable			10.00%
System One
Accounting Policies [Line Items]
Goodwill		$ 41,100
In-Center
Accounting Policies [Line Items]
Goodwill		500
Services
Accounting Policies [Line Items]
Asset impairment recognized		300	$ 500	$ 200
Goodwill		1,100
Federal
Accounting Policies [Line Items]
Net operating loss carryforward		390,000
State
Accounting Policies [Line Items]
Net operating loss carryforward		$ 182,000
Accounting Standards Update 2014-09 | Scenario, Forecast | Services
Accounting Policies [Line Items]
Goodwill, impairment loss	$ 1,100
Accounting Standards Update 2016-09 | Federal
Accounting Policies [Line Items]
Net operating loss carryforward	18,000
Accounting Standards Update 2016-09 | State
Accounting Policies [Line Items]
Net operating loss carryforward	$ 1,600

Summary of Significant Accoun47

Summary of Significant Accounting Policies - Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at Beginning of Year	$ 535	$ 417	$ 425
Provision	471	179	20
Write-offs	(191)	(61)	(28)
Balance at End of Year	$ 815	$ 535	$ 417

Summary of Significant Accoun48

Summary of Significant Accounting Policies - Estimated Useful Lives of Property and Equipment and Field Equipment (Details)	12 Months Ended
	Dec. 31, 2017
Buildings
Property, Plant and Equipment [Line Items]
Estimated useful life	30 years
Equipment and tooling | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Equipment and tooling | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	12 years
Computer and office equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Computer and office equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Molds | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Molds | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	7 years
Furniture | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Furniture | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	7 years
Field equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Field equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	7 years

Summary of Significant Accoun49

Summary of Significant Accounting Policies - Schedule of Rollforward of Warranty Accrual (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Standard and Extended Product Warranty Accrual, Increase (Decrease) [Roll Forward]
Balance at Beginning of Year	$ 280	$ 389	$ 287
Provision	445	457	526
Usage	(432)	(566)	(424)
Balance at End of Year	$ 293	$ 280	$ 389

Inventory - Components of Inven

Inventory - Components of Inventory (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Purchased components	$ 14,947	$ 14,967
Work in process	13,433	13,939
Finished goods	20,832	17,939
Total	$ 49,212	$ 46,845

Property and Equipment, Field51

Property and Equipment, Field Equipment and Deferred Cost of Revenues - Summary of Components of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 117,056	$ 108,718
Less accumulated depreciation	(56,794)	(47,157)
Property and equipment, net	60,262	61,561
Equipment and tooling
Property, Plant and Equipment [Line Items]
Property and equipment, gross	44,823	39,921
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	34,812	35,146
Computer and office equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	8,593	10,035
Molds
Property, Plant and Equipment [Line Items]
Property and equipment, gross	7,573	6,805
Furniture
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,612	3,561
Building
Property, Plant and Equipment [Line Items]
Property and equipment, gross	9,414	8,057
Land
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,091	956
Construction-in-process
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 7,138	$ 4,237

Property and Equipment, Field52

Property and Equipment, Field Equipment and Deferred Cost of Revenues - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation expense for property and equipment	$ 12.2	$ 11.6	$ 10.4
Capitalized computer development costs	0.9	1.8
Amortization of capitalized computer development costs	0.9	0.9	0.9
Amortization expense of deferred cost of revenue	13.1	13.3	$ 12.6
Germany
Property, Plant and Equipment [Line Items]
Capital lease obligation	12
Deferred revenues	6.4
Manufacturing facility in Germany | Germany
Property, Plant and Equipment [Line Items]
Fair value in relation with incremental borrowing rate			50.00%
Field equipment
Property, Plant and Equipment [Line Items]
Depreciation expense for field equipment	$ 6.2	$ 5.5	$ 5

Property and Equipment, Field53

Property and Equipment, Field Equipment and Deferred Cost of Revenues - Components of Assets Subject to Capital Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Less accumulated depreciation	$ (8,979)	$ (6,402)
Assets subject to capital leases, net	19,609	17,629
Manufacturing facility in Germany | Germany
Property, Plant and Equipment [Line Items]
Manufacturing facility in Germany/Other assets subject to capital leases	24,135	21,007
Other assets subject to capital lease
Property, Plant and Equipment [Line Items]
Manufacturing facility in Germany/Other assets subject to capital leases	$ 4,453	$ 3,024

Property and Equipment, Field54

Property and Equipment, Field Equipment and Deferred Cost of Revenues - Components of Field Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Field equipment, net	$ 24,264	$ 22,309
Field equipment
Property, Plant and Equipment [Line Items]
Field equipment	75,823	70,743
Less accumulated depreciation	(51,559)	(48,434)
Field equipment, net	$ 24,264	$ 22,309

Property and Equipment, Field55

Property and Equipment, Field Equipment and Deferred Cost of Revenues - Components of Deferred Costs of Revenue (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Deferred costs of revenues	$ 137,734	$ 126,375
Less accumulated amortization	(106,324)	(93,210)
Deferred Costs, Net	$ 31,410	$ 33,165

Intangible Assets - Summary of

Intangible Assets - Summary of Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Cost	$ 34,651	$ 34,638
Accumulated Amortization	(26,991)	(24,950)
Bloodline, needle and other patented and unpatented technology
Finite-Lived Intangible Assets [Line Items]
Cost	6,200	6,200
Accumulated Amortization	$ (6,200)	(6,200)
Useful Life	8 years
Trade names
Finite-Lived Intangible Assets [Line Items]
Cost	$ 2,300	2,300
Accumulated Amortization	$ (1,684)	(1,520)
Useful Life	14 years
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Cost	$ 26,151	26,138
Accumulated Amortization	$ (19,107)	$ (17,230)
Customer relationships | Minimum
Finite-Lived Intangible Assets [Line Items]
Useful Life	10 years
Customer relationships | Maximum
Finite-Lived Intangible Assets [Line Items]
Useful Life	14 years

Intangible Assets - Additional

Intangible Assets - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 2	$ 2	$ 2.6

Intangible Assets - Estimated A

Intangible Assets - Estimated Aggregated Amortization Expense for Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
2,018	$ 2,036
2,019	2,036
2,020	2,036
2,021	1,552
Total	$ 7,660	$ 9,688

Net Loss per Share - Schedule o

Net Loss per Share - Schedule of Anti-dilutive Net Loss Per Share (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common stock equivalents excluded from computation of earnings per share (in shares)	1,324	1,146	1,082
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common stock equivalents excluded from computation of earnings per share (in shares)	1,100	785	732
Unvested restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common stock equivalents excluded from computation of earnings per share (in shares)	224	361	350

Accrued Expenses, Other Curre60

Accrued Expenses, Other Current Liabilities, and Other Long Term Liabilities - Components of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Payroll, compensation and related benefits	$ 13,195	$ 14,086
Distribution expenses	4,914	4,804
General and administrative expenses	1,670	4,415
Other	8,206	7,680
Total	$ 27,985	$ 30,985

Accrued Expenses, Other Curre61

Accrued Expenses, Other Current Liabilities, and Other Long Term Liabilities - Components of Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Capital lease obligations	$ 2,131	$ 1,840
Deferred revenue, current portion	1,473	1,035
Other	955	895
Total	$ 4,559	$ 3,770

Accrued Expenses, Other Curre62

Accrued Expenses, Other Current Liabilities, and Other Long Term Liabilities - Components of Other Long-term Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Capital lease obligations	$ 11,589	$ 9,991
Lease incentive obligations	2,652	3,059
Benefit plan obligations	2,060	1,678
Other	1,523	840
Total	$ 17,824	$ 15,568

Debt and Capital Lease Obliga63

Debt and Capital Lease Obligations - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	May 31, 2017	Dec. 31, 2017
Debt Instrument [Line Items]
Extinguishment amount of debt	$ 900,000
Secured Debt
Debt Instrument [Line Items]
Loans secured by certain assets		$ 1,118,000
Secured Debt | Minimum
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage		2.00%
Mortgage loan period		5 years
Secured Debt | Maximum
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage		6.00%
Mortgage loan period		10 years
Capital Lease Obligations
Debt Instrument [Line Items]
Mortgage loan period	5 years
Revolving Line of Credit with Capital One Financial Corporation and SVB | Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Maximum amount borrowed under new revolving line of credit		$ 35,000,000
Revolving Line of Credit with Capital One Financial Corporation and SVB | Revolving Credit Facility | Line of Credit | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Revolving line of credit, borrowing interest rate		2.50%
Variable rate description, spread		1.00%
Revolving Line of Credit with Capital One Financial Corporation and SVB | Revolving Credit Facility | Line of Credit | Base Rate
Debt Instrument [Line Items]
Revolving line of credit, borrowing interest rate		1.50%
Revolving Line of Credit with Capital One Financial Corporation and SVB | Revolving Credit Facility | Line of Credit | Federal Funds Effective Swap Rate
Debt Instrument [Line Items]
Variable rate description, spread		0.50%

Debt and Capital Lease Obliga64

Debt and Capital Lease Obligations - Schedule of Future Minimum Payments Under Capital Leases (Details) $ in Thousands	Dec. 31, 2017USD ($)
Debt Disclosure [Abstract]
2,018	$ 1,674
2,019	1,733
2,020	1,792
2,021	1,932
2,022	1,820
Thereafter	7,539
Total minimum lease payments	16,490
Less: Amount representing interest	(2,770)
Present value of future minimum lease payments	13,720
Estimated residual value of manufacturing facility	$ 6,900

Business Segment and Geograph65

Business Segment and Geographic Information - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017segment
Segment Reporting [Abstract]
Number of reporting segments	3

Business Segment and Geograph66

Business Segment and Geographic Information - Summary of Operating Performance of Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues	$ 103,601	$ 97,295	$ 96,216	$ 96,829	$ 93,013	$ 91,951	$ 92,207	$ 89,207	$ 393,941	$ 366,378	$ 336,123
Segment profit (loss)	(1,831)	$ (8,283)	$ (2,056)	$ (1,681)	(2,154)	$ 24	$ (1,180)	$ (975)	(13,851)	(4,285)	(14,629)
Depreciation and amortization									33,754	32,637	30,715
Segment assets	325,629				317,207				325,629	317,207	306,874
System One
Segment Reporting Information [Line Items]
Revenues									306,361	283,923	247,775
Segment profit (loss)									82,585	74,912	59,748
Depreciation and amortization									22,166	23,671	20,554
Segment assets	134,825				135,038				134,825	135,038	120,253
In-Center
Segment Reporting Information [Line Items]
Revenues									61,307	63,038	74,768
Segment profit (loss)									8,070	10,092	12,395
Depreciation and amortization									2,121	2,003	1,835
Segment assets	25,225				21,246				25,225	21,246	24,232
Services
Segment Reporting Information [Line Items]
Revenues									19,539	14,781	6,412
Segment profit (loss)									(23,702)	(26,233)	(23,826)
Depreciation and amortization									5,217	4,781	3,322
Segment assets	19,712				23,620				19,712	23,620	19,547
Operating Segments
Segment Reporting Information [Line Items]
Segment assets	179,762				179,904				179,762	179,904
Operating Segments | System One
Segment Reporting Information [Line Items]
Revenues									301,299	276,393	244,641
Operating Segments | In-Center
Segment Reporting Information [Line Items]
Revenues									61,307	63,038	74,768
Operating Segments | Services
Segment Reporting Information [Line Items]
Revenues									19,539	14,781	6,412
Other
Segment Reporting Information [Line Items]
Revenues									11,796	12,166	10,302
Segment profit (loss)									(80,804)	(62,309)	(62,946)
Depreciation and amortization									4,349	4,427	5,004
Segment assets	146,737				138,273				146,737	138,273	142,842
Intersegment Elimination
Segment Reporting Information [Line Items]
Revenues									(5,062)	(7,530)	(3,134)
Segment profit (loss)									0	(747)
Depreciation and amortization									(99)	(2,245)
Segment assets	$ (870)				$ (970)				(870)	(970)
Intersegment Elimination | System One
Segment Reporting Information [Line Items]
Revenues									$ 5,062	$ 7,530	$ 3,134

Business Segment and Geograph67

Business Segment and Geographic Information - Reconciliation of Total Segment Assets to Total Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting, Asset Reconciling Item [Line Items]
Segment assets	$ 325,629	$ 317,207	$ 306,874
Cash and cash equivalents	64,928	59,632	59,065	$ 52,884
Inventory	49,212	46,845
Property and equipment, net	60,262	61,561
Intangible assets, net	7,660	9,688
Goodwill	42,748	42,648
Total assets	325,629	317,207	306,874
Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Segment assets	179,762	179,904
Total assets	179,762	179,904
Intersegment Elimination
Segment Reporting, Asset Reconciling Item [Line Items]
Segment assets	(870)	(970)
Total assets	(870)	(970)
Other
Segment Reporting, Asset Reconciling Item [Line Items]
Segment assets	146,737	138,273	142,842
Cash and cash equivalents	64,927	59,632
Accounts Receivable, net	949	632
Inventory	305	0
Property and equipment, net	16,628	16,600
Intangible assets, net	7,660	9,688
Goodwill	42,748	42,648
Prepaid and other assets	13,520	9,073
Total assets	$ 146,737	$ 138,273	$ 142,842

Business Segment and Geograph68

Business Segment and Geographic Information - Total Long-Lived Tangible Assets by Geographic Area (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 84,526	$ 84,054	$ 87,455
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	42,610	46,724	46,551
Mexico
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	16,790	13,431	14,233
Other Americas
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	1,630	571	825
Total Americas
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	61,030	60,726	61,609
Germany
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	18,270	17,574	19,053
Other Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	5,226	5,754	6,793
Total Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 23,496	$ 23,328	$ 25,846

Business Segment and Geograph69

Business Segment and Geographic Information - Summary of Number of Customers Who Individually Make Up Greater than 10% of Total Revenues (Details) - Sales Revenue, Net - Customer Concentration Risk	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
DaVita
Revenue, Major Customer [Line Items]
Percentage of revenues	20.00%	20.00%	20.00%
Fresenius
Revenue, Major Customer [Line Items]
Percentage of revenues	20.00%	18.00%	17.00%

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)option	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Commitments and Contingencies [Line Items]
Rent expense	$ 5.3	$ 5	$ 4.5
Corporate Headquarters
Commitments and Contingencies [Line Items]
Initial lease period	11 years
Lease termination provision, period	7 years
Leases, number of options to extend | option	2
Period of renewal of options	5 years
Percent of rent of the then fair market value	95.00%
Leasehold improvements allowance	$ 4.3
NxStage Kidney Care Facility | Minimum
Commitments and Contingencies [Line Items]
Period of renewal of options	5 years
Leasehold improvements allowance	$ 0.1
NxStage Kidney Care Facility | Maximum
Commitments and Contingencies [Line Items]
Period of renewal of options	10 years
Leasehold improvements allowance	$ 0.3

Commitments and Contingencies71

Commitments and Contingencies - Future Minimum Rental Payments Under Operating Leases (Details) $ in Thousands	Dec. 31, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,018	$ 5,463
2,019	4,811
2,020	4,297
2,021	3,694
2,022	3,174
Thereafter	2,708
Total	$ 24,147

Commitments and Contingencies72

Commitments and Contingencies - Purchase Commitments (Details) $ in Millions	Dec. 31, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
Purchase obligation, due in next twelve months	$ 9.6
Purchase obligation, due in second and third year	10
Purchase obligation, due in fourth and fifth year	0.7
Purchase obligation	$ 20.3

Income Taxes - Summary of Incom

Income Taxes - Summary of Income (Loss) Before Income Taxes by Geography (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
U.S.	$ (19,314)	$ (9,265)	$ (17,672)
Foreign	3,844	3,050	2,489
Net loss before income taxes	$ (15,470)	$ (6,215)	$ (15,183)

Income Taxes - Components of Pr

Income Taxes - Components of Provision for (Benefit from) Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
U.S. - Federal	$ (1,269)	$ 0	$ 0
U.S. - State	96	73	86
Foreign	1,540	1,200	1,225
Total Current	367	1,273	1,311
Deferred:
Foreign	(512)	(171)	(234)
Total Deferred	(512)	(171)	(234)
Total Provision	$ (145)	$ 1,102	$ 1,077

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Jan. 01, 2018	Dec. 31, 2016	Dec. 31, 2015
Schedule of Income Tax [Line Items]
Effective income tax rate reconciliation, allocation adjustments, amount	$ 1,300
Tax cuts and jobs act of 2017, incomplete accounting, change in tax rate, provisional income tax expense (benefit)	53,000
Net operating loss carryforwards, deferred tax assets	92,315		$ 115,151
Decrease in deferred tax valuation allowance	23,800
Decrease in unrecognized tax benefits is reasonably possible	1,500
Unrecognized tax benefits	800
Interest and penalties accrued (less than)	100		$ 100	$ 100
Undistributed earnings of foreign subsidiaries	0
Federal
Schedule of Income Tax [Line Items]
Net operating loss carryforward	390,000
Federal | Research
Schedule of Income Tax [Line Items]
Research and development credit carryforward	8,500
State
Schedule of Income Tax [Line Items]
Net operating loss carryforward	182,000
State | Research
Schedule of Income Tax [Line Items]
Research and development credit carryforward	3,000
Tax credit carryforward, net	3,900
Foreign | Research
Schedule of Income Tax [Line Items]
Research and development credit carryforward	$ 1,000
Accounting Standards Update 2016-09 | Federal
Schedule of Income Tax [Line Items]
Net operating loss carryforwards, deferred tax assets		$ 52,900
Net operating loss carryforward		18,000
Accounting Standards Update 2016-09 | State
Schedule of Income Tax [Line Items]
Net operating loss carryforwards, deferred tax assets		34,300
Net operating loss carryforward		$ 1,600

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of U.S. Federal Statutory Tax Rate to Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal statutory rate	34.00%	34.00%	34.00%
Stock compensation	25.70%	(1.50%)	(2.50%)
State income tax, net of federal tax benefit	2.30%	(2.30%)	(2.80%)
U.S. research credits	6.70%	18.90%	(0.30%)
Foreign income inclusion in the U.S.	(4.70%)	(10.40%)	(5.00%)
Valuation allowance	149.40%	(47.40%)	(25.80%)
Change in tax reserves	(1.40%)	(0.50%)	(0.50%)
Minority Interest	(1.60%)	(15.90%)	(0.90%)
Tax Reform impact	(344.60%)	(0.00%)	(0.00%)
Intraperiod tax allocation	8.20%	(0.00%)	(0.00%)
ASU 2016-09	126.70%	(0.00%)	(0.00%)
Other, net	0.20%	7.40%	(3.30%)
Effective tax rate	0.90%	(17.70%)	(7.10%)

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 92,315	$ 115,151
Tax credits	12,706	11,180
Stock-based compensation	4,922	7,339
Capitalized research and development	1,126	2,167
Financing liabilities	5,531	5,161
Other	7,613	8,349
Total deferred tax assets	124,213	149,347
Deferred tax liabilities:
Fixed assets	(5,485)	(5,754)
Intangible assets	(1,902)	(3,606)
Other	(222)	(187)
Total deferred tax liabilities	(7,609)	(9,547)
Net deferred tax assets before valuation allowance	116,604	139,800
Less valuation allowance	(115,035)	(138,795)
Net deferred tax assets	$ 1,569	$ 1,005

Income Taxes - Changes in Unrec

Income Taxes - Changes in Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of the year	$ 517	$ 379	$ 347
Increase in unrecognized tax benefits as a result of tax positions taken during the current year	275	89	66
Increase (decrease) in unrecognized tax benefits as a result of tax positions taken during a prior year	50	115	(34)
Reductions due to lapse of applicable statute of limitations	(78)	(66)	0
Balance at end of year	$ 764	$ 517	$ 379

Stock Plans and Stock-Based C79

Stock Plans and Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vests over a requisite service period		3 years
Fair value of options vested		$ 6,700	$ 6,100	$ 4,800
Aggregate intrinsic value of options exercised		$ 15,300	$ 5,600	$ 10,400
Shares, granted (in shares)		675,358
Shares issued under employee stock purchase plan (in shares)		36,253	37,531	50,343
Share-based compensation expense		$ 11,537	$ 10,117	$ 12,598
Unrecognized stock compensation cost		$ 20,200
Weighted average period		2 years 8 months 12 days
Options to Purchase Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average fair value of options granted (in dollars per share)		$ 9.92	$ 5.89	$ 6.16
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average fair value of restricted stock granted (in dollars per share)		$ 25.10	$ 16.33	$ 16.71
Total fair value of restricted stock		$ 4,800	$ 5,100	$ 5,500
2014 Omnibus Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option expiration period		10 years
Reduction in number of shares available for grant (in shares)		1.62
Number of shares authorized for grant (in shares)		5,600,000
Share available for grant (in shares)		7,800,000
2014 Omnibus Incentive Plan | Restricted Stock Units (RSUs) | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		3 years
2014 Omnibus Incentive Plan | Restricted Stock Units (RSUs) | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
2014 Omnibus Incentive Plan | Options to Purchase Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
2014 Omnibus Incentive Plan | Options to Purchase Common Stock | Board of Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		1 year
Employee Stock Purchase Plan 2005
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock vests over a requisite service period		3 months
Number of shares authorized for grant (in shares)		850,000
Share available for grant (in shares)		200,000
Offering period		6 months
Number of minimum weekly hours of employment		20 hours
Price at which employee can purchase common stock in an offering percentage		95.00%
Weighted-average fair value of restricted stock granted (in dollars per share)		$ 4.06	$ 4.07	$ 1.74
Share-based compensation expense		$ 100	$ 200	$ 100
2017 Performance Awards | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Shares, granted (in shares)	231,384
Weighted-average fair value of restricted stock granted (in dollars per share)	$ 23.14

Stock Plans and Stock-Based C80

Stock Plans and Stock-Based Compensation - Summary of Status of Stock Options Granted Under All Plans (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares
Shares
Shares, outstanding at beginning of year (in shares) | shares	4,656,405
Shares, granted (in shares) | shares	675,358
Shares, exercised (in shares) | shares	(1,130,939)
Shares, forfeited or expired (in shares) | shares	(83,627)
Shares, outstanding at end of year (in shares) | shares	4,117,197
Shares, fully vested and exercisable (in shares) | shares	2,684,405
Shares, fully vested, exercisable and expected to vest (in shares) | shares	4,002,574
Weighted Average Exercise Price
Weighted average exercise price, outstanding at beginning of year (in dollars per share) | $ / shares	$ 15.02
Weighted average exercise price, granted (in dollars per share) | $ / shares	26.87
Weighted average exercise price, exercised (in dollars per share) | $ / shares	13.79
Weighted average exercise price, forfeited or expired (in dollars per share) | $ / shares	20.50
Weighted average exercise price, outstanding at end of year (in dollars per share) | $ / shares	17.19
Weighted average exercise price, fully vested and exercisable (in dollars per share) | $ / shares	15.90
Weighted average exercise price, fully vested, exercisable and expected to vest (in dollars per share) | $ / shares	$ 17.12
Aggregate intrinsic value, outstanding at end of year | $	$ 30,825
Aggregate intrinsic value, fully vested and exercisable | $	22,730
Aggregate intrinsic value, fully vested, exercisable and expected to vest | $	$ 30,177
Average remaining contractual life, outstanding at end of year	6 years 9 months
Average remaining contractual life, fully vested and exercisable	6 years 18 days
Average remaining contractual life, fully vested, exercisable and expected to vest	6 years 8 months 16 days

Stock Plans and Stock-Based C81

Stock Plans and Stock-Based Compensation - Estimated Fair Value of Options at Date of Grant (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0.00%
Options to Purchase Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, lower range	1.79%	1.20%	1.34%
Risk-free interest rate, upper range	2.13%	2.45%	2.27%
Expected stock price volatility, lower range	36.80%	38.00%	38.00%
Expected stock price volatility, upper range	38.80%	43.05%	42.52%
Expected dividend yield	0.00%	0.00%	0.00%
Options to Purchase Common Stock | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life (in years)	5 years	5 years	4 years 9 months 18 days
Options to Purchase Common Stock | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life (in years)	6 years 6 months	9 years 11 months 1 day	10 years

Stock Plans and Stock-Based C82

Stock Plans and Stock-Based Compensation - Summary of Status of Unvested Restricted Stock Units (Details) - Restricted Stock - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares
Shares, unvested at beginning of year (in shares)	1,143,800
Shares, granted (in shares)	407,279
Shares, vested (in shares)	(339,496)
Shares, forfeited (in shares)	(499,253)
Shares, unvested at end of year (in shares)	712,330	1,143,800
Weighted Average Grant-date Fair Value
Weighted average grant date fair value, unvested at beginning of year (in dollars per share)	$ 15.57
Weighted average grant date fair value, granted (in dollars per share)	25.10	$ 16.33	$ 16.71
Weighted average grant date fair value, vested (in dollars per share)	14.24
Weighted average grant-date fair value, forfeited (in dollars per share)	16.26
Weighted average grant date fair value, unvested at end of year (in dollars per share)	$ 21.17	$ 15.57
Aggregate Intrinsic Value
Aggregate intrinsic value unvested	$ 17,260
Weighted average remaining contractual life unvested, ending balance	2 years 1 month 21 days

Stock Plans and Stock-Based C83

Stock Plans and Stock-Based Compensation - Valuation Assumptions for ESPP (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0.00%
Employee Stock Purchase Plan 2005
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life (in months)	6 months	6 months	6 months
Risk-free interest rate, lower range	0.65%	0.37%	0.11%
Risk-free interest rate, upper range	1.13%	0.49%	0.13%
Expected stock price volatility, lower range	36.40%	39.60%	18.40%
Expected stock price volatility, upper range	39.20%	48.20%	22.40%
Expected dividend yield	0.00%	0.00%	0.00%

Stock Plans and Stock-Based C84

Stock Plans and Stock-Based Compensation - Summary of Stock-Based Compensation Expense in Consolidated Statements of Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 11,537	$ 10,117	$ 12,598
Cost of revenues
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	1,201	1,371	1,068
Selling and marketing
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	3,933	3,304	4,458
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	1,539	1,536	1,979
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 4,864	$ 3,906	$ 5,093

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Benefits [Abstract]
Percentage contribution by participant to the 401(k) Plan, maximum	75.00%
Employer contribution of first specific employee contribution percentage	100.00%
Employee contribution used to determine employer first contribution	3.00%
Employer contribution of next specific employee contribution percentage	50.00%
Employee contribution used to determine employer next contribution	2.00%
Company's contribution cost recognized	$ 2,700	$ 2,500	$ 1,800
Postemployment benefits liabilities, noncurrent	2,060	1,678
Expense recorded in connection of postemployment benefit plans	$ 0	$ 0	$ 0

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Shares delivered or surrendered in payment for the exercise of stock options (in shares)	110,510	114,301	49,786

Noncontrolling Interests - Addi

Noncontrolling Interests - Additional Information (Details) $ in Millions	Dec. 31, 2017USD ($)entity	Dec. 31, 2016USD ($)
Noncontrolling Interest [Abstract]
Number of VIEs | entity	5
Total assets of variable interest entities	$ 5.6	$ 8
Total liabilities and noncontrolling interest of variable interest entities	$ 5.8	$ 7.2

Noncontrolling Interests - Sche

Noncontrolling Interests - Schedule of Changes in Noncontrolling Interest (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Balance at beginning of period	$ 625	$ 1,694	$ 1,088
Capital contributions by noncontrolling interest	0	630	1,316
Sales of noncontrolling interests	0	679	208
Add: Accretion to redemption value of noncontrolling interests	481	0	0
Reclassification of noncontrolling interest subject to put provision	322	0	0
Net loss attributable to noncontrolling interest in consolidated subsidiary	(1,440)	(2,378)	(918)
Balance at end of period	$ (12)	$ 625	$ 1,694

Derivative Instruments and He89

Derivative Instruments and Hedging - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Hedging Transactions And Derivative Financial Instruments [Line Items]
Period of cash flow hedges	12 months
Gain (loss) on ineffectiveness in earnings	$ 0	$ 0	$ 0
Foreign Exchange Forward | Cash Flow Hedges
Hedging Transactions And Derivative Financial Instruments [Line Items]
Notional amount of outstanding contracts	24,108,418.88	18,649,479.65
Fair value of outstanding contracts liability		$ 1,800,000
Maximum | Foreign Exchange Forward | Cash Flow Hedges
Hedging Transactions And Derivative Financial Instruments [Line Items]
Fair value of outstanding contracts asset	$ 100,000

Derivative Instruments and He90

Derivative Instruments and Hedging - Effect of Contracts Designated as Cash Flow Hedges on Consolidated Financial Statements (Details) - Foreign Exchange Forward - Cost of revenues - Cash Flow Hedges - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	$ 3,433	$ (2,712)	$ (2,140)
Gain (Loss) Reclassified from OCI into Income (Effective Portion)	$ 1,163	$ (1,910)	$ (1,745)

Accumulated Other Comprehensi91

Accumulated Other Comprehensive Income - Summary of Additional Information on Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 202,023	$ 193,520	$ 191,555
Other comprehensive income (loss), net of tax:	2,428	(2,070)	(1,839)
Ending balance	213,146	202,023	193,520
Other comprehensive income, tax	1,269
Unrealized gain (loss) on derivative instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(2,285)	(1,483)	(1,088)
Other comprehensive income before reclassifications	2,164	(2,712)	(2,140)
(Gain) Loss reclassified to earnings	(1,163)	1,910	1,745
Other comprehensive income (loss), net of tax:	1,001	(802)	(395)
Ending balance	(1,284)	(2,285)	(1,483)
Other
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(3,816)	(2,548)	(1,104)
Other comprehensive income before reclassifications	1,427	(1,268)	(1,444)
(Gain) Loss reclassified to earnings	0	0	0
Other comprehensive income (loss), net of tax:	1,427	(1,268)	(1,444)
Ending balance	(2,389)	(3,816)	(2,548)
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(6,101)	(4,031)	(2,192)
Other comprehensive income before reclassifications	3,591	(3,980)	(3,584)
(Gain) Loss reclassified to earnings	(1,163)	1,910	1,745
Other comprehensive income (loss), net of tax:	2,428	(2,070)	(1,839)
Ending balance	$ (3,673)	$ (6,101)	$ (4,031)

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Fair Value Measurements, Recurring Basis - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Foreign exchange forward contracts
Assets
Foreign exchange forward contracts	$ 690	$ 0
Liabilities
Foreign exchange forward contracts	661	1,771
Foreign exchange forward contracts | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Foreign exchange forward contracts	0	0
Liabilities
Foreign exchange forward contracts	0	0
Foreign exchange forward contracts | Significant Other Observable Inputs (Level 2)
Assets
Foreign exchange forward contracts	690	0
Liabilities
Foreign exchange forward contracts	661	1,771
Foreign exchange forward contracts | Significant Unobservable Inputs (Level 3)
Assets
Foreign exchange forward contracts	0	0
Liabilities
Foreign exchange forward contracts	0	0
Money market funds
Assets
Money market funds	35,020	34,804
Money market funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Money market funds	35,020	34,804
Money market funds | Significant Other Observable Inputs (Level 2)
Assets
Money market funds	0	0
Money market funds | Significant Unobservable Inputs (Level 3)
Assets
Money market funds	$ 0	$ 0

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Ownership percentage				2.50%
Payments to acquire investments	$ 2,500	$ 0	$ 0

Supplemental Cash Flow Inform94

Supplemental Cash Flow Information - Summary of Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Disclosures:
Cash paid for interest	$ 638	$ 639	$ 703
Cash paid for taxes	1,258	983	919
Noncash Investing and Financing Activities:
Transfers from inventory to field equipment	19,257	20,920	16,675
Transfers from field equipment to deferred cost of revenues	11,026	13,400	11,638
Payment of corporate bonus plan in common stock	0	0	1,103
Market value of shares received in payment for exercise of stock options	3,100	2,320	875
Construction-in-process financed by construction liability	142	187	1,332
Add: Accretion to redemption value of noncontrolling interests	481	0	0
Property and equipment acquired under capital lease	0	127	354
Acquisition of business	0	0	513
Increase in deferred revenues related to the new manufacturing facility in Germany	0	0	663
Capital contributions by noncontrolling interest	$ 0	$ 54	$ 325

Quarterly Financial Data (Una95

Quarterly Financial Data (Unaudited) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 103,601	$ 97,295	$ 96,216	$ 96,829	$ 93,013	$ 91,951	$ 92,207	$ 89,207	$ 393,941	$ 366,378	$ 336,123
Gross profit	45,325	40,607	41,166	41,190	37,864	39,181	38,423	36,517	168,288	151,985	131,471
Loss from operations	(1,831)	(8,283)	(2,056)	(1,681)	(2,154)	24	(1,180)	(975)	(13,851)	(4,285)	(14,629)
Net loss	(2,311)	(8,894)	(2,579)	(1,541)	(2,419)	(890)	(2,225)	(1,783)	(15,325)	(7,317)	(16,260)
Net loss attributable to stockholders of NxStage Medical, Inc.	(2,269)	(8,445)	(2,089)	(1,189)	(1,597)	(166)	(1,732)	(1,276)	(13,992)	(4,771)	(15,342)
Net loss attributable to common stockholders	$ (2,269)	$ (8,926)	$ (2,089)	$ (1,189)	$ (1,597)	$ (166)	$ (1,732)	$ (1,276)	$ (14,473)	$ (4,771)	$ (15,342)
Net loss per share, basic and diluted (in dollars per share)	$ (0.03)	$ (0.14)	$ (0.03)	$ (0.02)	$ (0.02)	$ 0	$ (0.03)	$ (0.02)	$ (0.22)	$ (0.07)	$ (0.24)