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.

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.