NxStage Medical 10-K 26 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Feb. 17, 2015	Jun. 30, 2014
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Trading Symbol	NXTM
Entity Registrant Name	NxStage Medical, Inc.
Entity Central Index Key	1333170
Current Fiscal Year End Date	-19
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		62,707,290
Entity Public Float			$870

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$52,884	$84,134
Accounts receivable, net	24,099	20,158
Inventory	45,401	37,801
Prepaid expenses and other current assets	6,767	4,027
Total current assets	129,151	146,120
Property and equipment, net	66,574	52,478
Field equipment, net	21,118	13,041
Deferred cost of revenues	34,039	34,730
Intangible assets, net	14,370	17,194
Goodwill	41,817	41,817
Other assets	2,657	1,582
Total assets	309,726	306,962
Current liabilities:
Accounts payable	13,845	14,610
Accrued expenses	24,653	21,025
Current portion of long-term debt	93	102
Other current liabilities	6,165	1,870
Total current liabilities	44,756	37,607
Deferred revenues	52,943	53,277
Long-term debt	848	1,044
Other long-term liabilities	19,624	20,273
Total liabilities	118,171	112,201
Commitments and contingencies (Note 10)
Stockholders' equity:
Undesignated preferred stock: par value $0.001, 5,000,000 shares authorized; no shares issued and outstanding as of December 31, 2014 and 2013
Common stock: par value $0.001, 100,000,000 shares authorized; 63,429,005 and 61,666,048 shares issued as of December 31, 2014 and 2013, respectively	63	61
Additional paid-in capital	593,073	567,468
Accumulated deficit	-387,488	-363,542
Accumulated other comprehensive (loss) income	-2,192	212
Treasury stock, at cost: 772,273 and 575,895 shares as of December 31, 2014 and 2013, respectively	-12,989	-9,963
Total NxStage Medical, Inc. stockholders' equity	190,467	194,236
Noncontrolling interest	1,088	525
Total stockholders' equity	191,555	194,761
Total liabilities and stockholders' equity	$309,726	$306,962

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Undesignated preferred stock, par value	$0.00	$0.00
Undesignated preferred stock, shares authorized	5,000,000	5,000,000
Undesignated preferred stock, shares issued	0	0
Undesignated preferred stock, shares outstanding	0	0
Common stock, par value	$0.00	$0.00
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	63,429,005	61,666,048
Treasury stock, shares	772,273	575,895

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Loss (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Revenues	$301,501	$263,429	$242,132
Cost of revenues	185,598	160,926	149,324
Gross profit	115,903	102,503	92,808
Operating expenses:
Selling and marketing	55,385	47,842	40,485
Research and development	22,635	18,887	17,111
Distribution	26,001	21,246	18,888
General and administrative	34,069	32,326	27,530
Total operating expenses	138,090	120,301	104,014
Loss from operations	-22,187	-17,798	-11,206
Other expense:
Interest expense	-863	-611	-2,766
Other expense, net	-10	-397	-148
Total other expenses	-873	-1,008	-2,914
Net loss before income taxes	-23,060	-18,806	-14,120
Provision for (benefit from) income taxes	1,253	-245	1,033
Net loss	-24,313	-18,561	-15,153
Less: Net loss attributable to noncontrolling interests	-367
Net loss attributable to stockholders of NxStage Medical, Inc.	-23,946	-18,561	-15,153
Net loss per share, basic and diluted	($0.39)	($0.31)	($0.26)
Weighted-average shares outstanding, basic and diluted	61,700	60,261	57,890
Other comprehensive (loss) income, net of tax	-2,404	-258	538
Total comprehensive loss	-26,717	-18,819	-14,615
Less: Comprehensive loss attributable to noncontrolling interests	-367
Total comprehensive loss attributable to stockholders of NxStage Medical, Inc.	($26,350)	($18,819)	($14,615)

Consolidated_Statements_of_Cha

Consolidated Statements of Changes in Stockholders' Equity (USD $)	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Parent [Member]	Noncontrolling Interest [Member]
In Thousands, except Share data
Beginning balance at Dec. 31, 2011	$151,186	$56	$489,542	($329,828)	($68)	($8,516)	$151,186
Beginning balance, Shares at Dec. 31, 2011		56,167,090
Net loss	-15,153			-15,153			-15,153
Adjustments to other comprehensive loss, net of tax	538				538		538
Issuance of common stock, net of issuance costs	44,554	2	45,074			-522	44,554
Issuance of common stock, net of issuance costs, Shares		2,456,246
Exercise of stock options	5,832	1	6,344			-513	5,832
Exercise of stock options, Shares		913,066
Shares issued under employee restricted stock plans	-1,173		-1,173				-1,173
Shares issued under employee restricted stock plans, Shares		200,587
Shares issued under employee bonus plans	878		878				878
Shares issued under employee bonus plans, Shares		47,533
Shares issued under employee stock purchase plan	731		731				731
Shares issued under employee stock purchase plan, Shares		56,691
Shares issued to Directors in lieu of cash	138		138				138
Shares issued to Directors in lieu of cash, Shares		8,904
Stock-based compensation expense	10,060		10,060				10,060
Ending balance at Dec. 31, 2012	197,591	59	551,594	-344,981	470	-9,551	197,591
Ending balance, Shares at Dec. 31, 2012		59,850,117
Net loss	-18,561			-18,561			-18,561
Adjustments to other comprehensive loss, net of tax	-258				-258		-258
Exercise of stock options	4,255	1	4,666			-412	4,255
Exercise of stock options, Shares		662,767
Exercise of warrants	893	1	892				893
Exercise of warrants, Shares		874,921
Shares issued under employee restricted stock plans	-424		-424				-424
Shares issued under employee restricted stock plans, Shares		105,573
Shares issued under employee bonus plans	1,034		1,034				1,034
Shares issued under employee bonus plans, Shares		93,778
Shares issued under employee stock purchase plan	759		759				759
Shares issued under employee stock purchase plan, Shares		75,301
Shares issued to Directors in lieu of cash	42		42				42
Shares issued to Directors in lieu of cash, Shares		3,591
Stock-based compensation expense	8,905		8,905				8,905
Contributions from noncontrolling interest	525							525
Ending balance at Dec. 31, 2013	194,761	61	567,468	-363,542	212	-9,963	194,236	525
Ending balance, Shares at Dec. 31, 2013		61,666,048
Net loss	-24,313			-23,946			-23,946	-367
Adjustments to other comprehensive loss, net of tax	-2,404				-2,404		-2,404
Exercise of stock options	10,751	2	13,775			-3,026	10,751
Exercise of stock options, Shares	1,524,601	1,524,601
Shares issued under employee restricted stock plans	-422		-422				-422
Shares issued under employee restricted stock plans, Shares		166,127
Shares issued under employee stock purchase plan	804		804				804
Shares issued under employee stock purchase plan, Shares		70,899
Shares issued to Directors in lieu of cash	18		18				18
Shares issued to Directors in lieu of cash, Shares		1,330
Stock-based compensation expense	11,430		11,430				11,430
Contributions from noncontrolling interest	930							930
Ending balance at Dec. 31, 2014	$191,555	$63	$593,073	($387,488)	($2,192)	($12,989)	$190,467	$1,088
Ending balance, Shares at Dec. 31, 2014		63,429,005

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net loss	($24,313)	($18,561)	($15,153)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation and amortization	27,697	24,848	23,673
Stock-based compensation	12,881	8,638	11,403
Other	1,877	2,628	3,517
Changes in operating assets and liabilities:
Accounts receivable	-4,188	-1,095	-3,141
Inventory	-35,063	-20,076	-14,545
Prepaid expenses and other assets	-2,214	-484	-1,623
Accounts payable	-212	-2,233	839
Accrued expenses and other liabilities	4,235	1,081	5,263
Deferred revenues	-973	-4,887	-3,992
Net cash (used in) provided by operating activities	-20,273	-10,141	6,241
Cash flows from investing activities:
Cash paid for acquisition		-2,234
Purchases of property and equipment	-20,097	-16,246	-7,694
Net cash used in investing activities	-20,097	-18,480	-7,694
Cash flows from financing activities:
Proceeds from exercise of stock options and warrants and employee stock purchase plans	11,133	5,484	5,248
Investment by noncontrolling interest holder	930	525
Purchase of treasury stock			-522
Proceeds from loans and lines of credit		1,136
Repayments on loans and lines of credit	-98	-38
Payments on capital leases	-1,448	-1,352
Debt issuance costs	-1,056
Net cash provided by financing activities	9,461	5,755	4,726
Foreign exchange effect on cash and cash equivalents	-341	561	257
(Decrease) increase in cash and cash equivalents	-31,250	-22,305	3,530
Cash and cash equivalents, beginning of year	84,134	106,439	102,909
Cash and cash equivalents, end of year	$52,884	$84,134	$106,439

Nature_of_Operations

Nature of Operations	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Nature of Operations	1	Nature of Operations
	We are a medical device company that develops, manufactures and markets innovative products for the treatment of kidney failure, fluid overload and related blood treatments and procedures. Our primary product, the System One, was designed to satisfy an unmet clinical need for a system that can deliver the therapeutic flexibility and clinical benefits associated with 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, 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 including more frequent dialysis and nocturnal dialysis, which clinical literature suggests provides patients better clinical outcomes and improved quality of life. The System One is cleared or approved for commercial sale in the U.S., Canada and certain other markets, and is CE marked in the EU, for the treatment of acute and chronic kidney failure and fluid overload. The System One is cleared specifically by the U.S. Food and Drug Administration (FDA) for home hemodialysis and home nocturnal hemodialysis, as well as therapeutic plasma exchange in a clinical environment. The System One is also CE marked in the EU for home nocturnal hemodialysis. In February 2013, we received CE Mark approval and in April 2013 we received clearance from the FDA for the new high flow capabilities with the NxStage System One. We began selling the System One with this feature to both U.S. customers and international distributors in 2014. We also sell, through our Medisystems subsidiary, blood tubing sets and needles primarily to dialysis centers for the treatment of end-stage renal disease (ESRD). These products are cleared or approved for commercial sale in the U.S., Canada and certain other markets and are CE marked in the EU. We believe our largest market opportunity is for the System One used in the home dialysis market for the treatment of ESRD. We operate a small number of NxStage Kidney Care dialysis centers focused on supporting home therapy and providing flexible in-center options with NxStage technology as part of our market development activities to increase home therapy access. We continue to make significant investments in marketing, research and development, and these dialysis centers, all of which are intended to help us to further penetrate and expand the market for our products.

Summary_of_Significant_Account

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2	Summary of Significant Accounting Policies
	Principles of Consolidation and Basis of Presentation
	The accompanying consolidated financial statements include the accounts of NxStage Medical, Inc. and our wholly-owned and majority-owned subsidiaries. All material intercompany transactions and balances have been eliminated in consolidation.
	Use of Estimates
	The preparation of our consolidated financial statements in conformity with GAAP requires our management to make estimates and assumptions that affect reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
	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 market 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.
	System One Segment
	We derive revenue in the home market from the sales of hemodialysis therapy to customers in which the customer either purchases or rents the System One and/or PureFlow SL hardware and purchases a specified number of disposable products and service.
	For customers that purchase the System One and PureFlow SL hardware, in the U.S. 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 fees received from equipment sale 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 deferred and amortized over the same expected period as the related revenue. Disposable products revenue is recognized on a monthly basis upon delivery.
	Under the rental 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. Some of our distribution contracts for the In-Center segment contain minimum volume commitments with negotiated pricing discounts at different volume tiers. Each agreement may be canceled upon a material breach, subject to certain curing rights, and in many instances minimum volume commitments can be reduced or eliminated upon certain events.
	Services Segment
	Revenues in our Services segment are derived from dialysis care services provided to patients at our recently opened 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 (expense) income, 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 market value.
	Concentration of Credit Risk
	Financial instruments that potentially subject us to concentrations of credit risk consist principally of 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. Two customers represented 18% and 16% of accounts receivable at December 31, 2014 and one customer represented 19% of accounts receivable at December 31, 2013. 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, 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		Provision		Write-offs			Balance at
			Beginning of Year		(Recoveries)					End of Year
	December 31, 2014		$	321	$	219	$	(115	)	$	425
	December 31, 2013		$	424	$	47	$	(150	)	$	321
	December 31, 2012		$	510	$	—	$	(86	)	$	424
	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 Measures
	Certain financial and non financial assets and liabilities recorded at fair value have been classified as Level 1, 2 or 3 within the fair value hierarchy as described in the accounting standard. Fair values determined by Level 1 inputs utilize quoted prices (unadjusted) in active markets for identical assets or liabilities that we have the ability to access. Fair values determined by Level 2 inputs utilize data points that are observable such as quoted prices, interest rates and yield curves for similar instruments and model-derived valuations whose inputs are observable. Fair values determined by Level 3 inputs utilize unobservable data points for 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 record a provision for any excess or obsolete inventory when warranted based on remaining shelf-life and estimated future demand. 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 life 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, 2014 and 2013 primarily represents the costs of building, machinery, equipment under installation and software and computer costs.
	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
	Manufacturing equipment and tooling		3 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 computed using the straight-line method over the estimated economic lives of the respective intangible assets, ranging from eight to fourteen years. Long-lived assets, including intangible assets, are tested for recoverability whenever events or circumstances indicate that their carrying value may not be recoverable. The amount of impairment, if any, is measured based on fair value, which is determined using estimated discounted cash flows to be generated from such assets or group of assets. During 2014, 2013 and 2012, no such impairment was recognized. 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 fair value of the related net assets at the date of acquisition. We test goodwill at least annually for impairment, or more frequently when events or changes in circumstances indicate that the goodwill might be impaired. This impairment test is performed annually during the fourth quarter. 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. 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. Our reporting units with goodwill are our System One and In-center operating segments. During both 2014 and 2012, we utilized the qualitative assessment and concluded that it was more likely than not that the fair value of our reporting units was greater than their carrying value. During 2013, we utilized the quantitative assessment and concluded the fair value of the reporting units exceeds their carrying value, indicating that goodwill was not impaired. We estimated the fair value of our reporting units using a discounted cash flow approach which involves significant judgment with respect to future revenue growth, operating income, capital expenditures, changes in working capital use and the selection of a discount rate.
	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 generally 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		Provision		Usage			Balance at
		Beginning of Year							End of Year
December 31, 2014		$	297	$	441	$	(451	)	$	287
December 31, 2013		$	324	$	412	$	(439	)	$	297
December 31, 2012		$	380	$	540	$	(596	)	$	324
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 have accumulated significant losses since our inception in 1998. Utilization of the net operating losses may be subject to limitations and certain tax years in the respective tax jurisdictions remain open to examination.
Subsequent Events
Events occurring subsequent to December 31, 2014 have been evaluated for potential recognition or disclosure in the consolidated financial statements.
Recent Accounting Pronouncements
Effective January 1, 2014, we adopted Financial Accounting Standards Board (FASB) Accounting Standards Update (ASU) No. 2013-11, “Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists,” which impacts the presentation of unrecognized tax benefits on the statement of financial position. As a result, unrecognized tax benefits are presented as a reduction to a deferred tax asset for a net operating loss carryforward, a similar tax loss, or a tax credit carryforward. To the extent the tax benefit is not available at the reporting date under the governing tax law or if we do not intend to use the deferred tax asset for such purpose, the unrecognized tax benefit is presented as a liability and not combined with deferred tax assets. The adoption of this standard did not impact our condensed consolidated financial statements, as our practice was consistent with this standard prior to its effective date.
In May 2014, the FASB issued ASU No. 2014-09, “Revenue from Contracts with Customers,” which provides guidance for revenue recognition. The standard’s core principle is that a company will recognize revenue when it 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. The new guidance is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. Early application is not permitted. We are currently assessing the potential impact the adoption of this standard will have on our financial statements.
In August 2014, the FASB issued ASU No. 2014-15, “Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern” (“ASU 2014-15”), which expands upon principles that are currently in U.S. auditing standards by providing guidance on management’s responsibility in evaluating whether there is substantial doubt about a company’s ability to continue as a going concern and by providing related footnote disclosure requirements. The new guidance is effective for the annual period ending after December 15, 2016, and for annual periods and interim periods thereafter. Early adoption is permitted. We are currently evaluating the impact of this update but it is not expected to have a material impact on our financial statement disclosures.

Inventory

Inventory	12 Months Ended
	Dec. 31, 2014
Inventory Disclosure [Abstract]
Inventory	3	Inventory
	Inventory includes material, labor and overhead. The components of inventory are as follows (in thousands):
			December 31,
			2014		2013
	Purchased components		$	19,238	$	15,946
	Work in process			9,981		10,762
	Finished goods			16,182		11,093
			$	45,401	$	37,801

Property_and_Equipment_Field_E

Property and Equipment, Field Equipment and Deferred Cost of Revenues	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Property and Equipment, Field Equipment and Deferred Cost of Revenues	4	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,
			2014			2013
	Manufacturing equipment and tooling		$	34,621		$	24,963
	Leasehold improvements			18,485			11,883
	Computer and office equipment			8,935			4,132
	Molds			5,377			3,817
	Furniture			2,410			1,712
	Buildings			8,907			10,005
	Land			1,110			1,258
	Construction-in-process			14,609			16,500
				94,454			74,270
	Less accumulated depreciation			(27,880	)		(21,792	)
	Property and equipment, net		$	66,574		$	52,478
	Depreciation expense, including amortization of capital leases, for property and equipment was $7.1 million, $4.7 million and $3.7 million during 2014, 2013 and 2012, respectively.
	Included in construction-in-process as of December 31, 2013 was $4.5 million of capitalized computer development costs. There were no such costs included in construction-in-process at December 31, 2014. Capitalized computer development costs, net was $3.6 million at December 31, 2014 and we recognized amortization expense of $0.9 million during 2014.
	Our property and equipment includes the following amounts for assets subject to capital leases (amounts in thousands):
			December 31,
			2014
	Manufacturing facility in Germany		$	22,750
	Other assets subject to capital leases			2,438
	Less accumulated depreciation			(2,905	)
	Assets subject to capital leases, net		$	22,283
	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. Asahi funded construction costs of the facility, including land, building and equipment; however, given our involvement during construction we were considered the owner of the facility for accounting purposes and therefore, as required, we recorded the cost of the new facility within property and equipment on our consolidated balance sheet along with a corresponding liability within other long-term liabilities for the construction cost funded by Asahi.
	Pursuant to the Dialyzer Production Agreement, we agreed to 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 agreed to pay us cost including material, labor and overhead (but excluding depreciation on the new facility), plus applicable statutory value added or turnover tax established or required by law for each dialyzer manufactured by us for Asahi. We are required to pay Asahi a fixed amount per dialyzer manufactured for our own use in the facility, with such payments capped at fifty percent of the cost of the facility paid by Asahi. If the agreement is terminated subsequent to completion of construction by us, Asahi has the option to require us to purchase the facility from them or if the agreement is terminated by Asahi, we have the option to purchase the facility from them. In either case the purchase price is equal to one hundred percent of the then net book value of the facility, as calculated in accordance with GAAP.
	In December 2012 construction of the facility was completed, at which time the asset was placed in service. Given our continued involvement in the facility, we were precluded from derecognizing the cost of the facility or the corresponding liability. Therefore, the facility asset, including building and equipment, continued to be recorded within property and equipment, net, on our consolidated balance sheet and depreciated on a straight-line basis over its estimated useful life. The corresponding liability has been divided into two separate components, including a capital lease obligation and deferred revenue, based on their relative fair values at December 2012.
	In December 2014, construction of an additional production line within the facility was completed, at which time additional assets were placed into service at a total cost of $6.4 million. Consistent with the facility completed in December 2012, we were precluded from derecognizing the cost of the additional production line or the corresponding liability. Therefore, the asset is being recorded within property and equipment, net, on our consolidated balance sheet and depreciated on a straight-line basis over its estimated useful life. The corresponding liability has been divided into two separate components, including a capital lease obligation and deferred revenue, based on their relative fair values at December 2014 of $3.5 million and $2.9 million, respectively.
	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 asset paid by Asahi, and the estimated residual value of the 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 capital lease obligation has been classified within other long-term liabilities within our consolidated balances sheet with the amount expected to be paid within one year classified within other current liabilities. The capital lease obligation is decreased by payments made to Asahi for dialyzers manufactured for our own use and increased by interest expense.
	The fair value of the deferred revenue was determined using cost plus a reasonable margin for contract manufacturing in Germany, Level 3 inputs within the fair value hierarchy. The deferred revenue is recognized in revenues on a straight-line basis over the expected term of the Dialyzer Production Agreement.
	The capital lease obligation and deferred revenue balances are $12.7 million and $8.2 million, respectively, at December 31, 2014.
	Field Equipment, net
	The components of field equipment, net are as follows (in thousands):
			December 31,
			2014			2013
	Field equipment		$	61,132		$	49,695
	Less accumulated depreciation			(40,014	)		(36,654	)
	Field equipment, net		$	21,118		$	13,041
	Depreciation expense for field equipment, which is recorded in costs of revenues in the consolidated statements of comprehensive loss, was $4.2 million, $4.0 million and $3.7 million during 2014, 2013 and 2012, respectively.
	Deferred Costs of Revenues
	Amortization expense of direct costs relating to deferred equipment revenues was $13.5 million, $13.3 million and $13.5 million during 2014, 2013 and 2012, respectively.

Intangible_Assets

Intangible Assets	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	5	Intangible Assets
	The components of intangible assets, net are as follows (in thousands):
			December 31, 2014					December 31, 2013					Estimated
													Useful
			Cost		Accumulated			Cost		Accumulated			Life
					Amortization					Amortization
	Bloodline, needle and other patented and unpatented technology		$	6,200	$	(5,619	)	$	6,200	$	(4,844	)		8 years
	Trade names			2,300		(1,191	)		2,300		(1,026	)		14 years
	Customer relationships			26,175		(13,495	)		26,185		(11,621	)		10/14 years
	Intangible assets, net		$	34,675	$	(20,305	)	$	34,685	$	(17,491	)
	We recognized amortization expense of $2.8 million during each of 2014, 2013 and 2012.
	The estimated future aggregated amortization expense for intangible assets as of December 31, 2014 is as follows (in thousands):
	2015		$	2,621
	2016			2,040
	2017			2,040
	2018			2,040
	2019			2,040
	Thereafter			3,589
			$	14,370

Net_Loss_per_Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Net Loss per Share	6	Net Loss per Share
	Basic net loss per share is computed by dividing loss available 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,
			2014		2013		2012
	Options to purchase common stock			876		1,013		1,602
	Unvested restricted stock			236		152		196
	Warrants to purchase common stock			—		—		921
	Total			1,112		1,165		2,719

Accrued_Expenses_Other_Current

Accrued Expenses, Other Current Liabilities, and Other Long Term Liabilities	12 Months Ended
	Dec. 31, 2014
Payables and Accruals [Abstract]
Accrued Expenses, Other Current Liabilities, and Other Long Term Liabilities	7	Accrued Expenses, Other Current Liabilities, and Other Long Term Liabilities
	The components of accrued expenses are as follows (in thousands):
			December 31,
			2014		2013
	Payroll, compensation and related benefits		$	12,346	$	9,041
	Distribution expenses			3,069		2,762
	General and administrative expenses			3,075		2,207
	Audit, legal, and consulting fees			1,394		2,725
	Other			4,769		4,290
	Total		$	24,653	$	21,025
	The components of other current liabilities are as follows (in thousands):
			December 31,
			2014		2013
	Deferred revenue, current portion		$	2,195	$	—
	Capital lease obligations			2,246		1,471
	Other			1,724		399
	Total		$	6,165	$	1,870
	The components of other long term liabilities are as follows (in thousands):
			December 31,
			2014		2013
	Capital lease obligations		$	11,876	$	14,133
	Lease incentive obligations			4,569		3,589
	Benefit plan obligations			1,745		1,770
	Other			1,434		781
	Total		$	19,624	$	20,273

Debt_and_Capital_Lease_Obligat

Debt and Capital Lease Obligations	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Debt and Capital Lease Obligations	8	Debt and Capital Lease Obligations
	Manufacturing Facility in Italy
	We entered into two euro denominated mortgages collateralized by a manufacturing facility in Italy that we acquired in May 2013. The first mortgage is in the principal amount of $0.6 million, subject to an annual interest rate of 6.0%, and payable quarterly over a 10 year period. The second mortgage is in the principal amount of $0.5 million, subject to an annual interest rate of 2.0%, and payable biannually over a 10 year period.
	Loan and Security Agreements
	We had a loan and security agreement with Silicon Valley Bank, or SVB, that provided for a $15.0 million revolving line of credit. This agreement matured as of March 31, 2014.
	On June 10, 2014, we entered into a new revolving line of credit with General Electric Capital Corporation, or GECC, 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 new 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 new 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.
	As of December 31, 2014, there were no outstanding borrowings under the $35 million revolving line of credit, we were in compliance with all applicable covenants and, subject to the lenders’ adjustments described above, we had approximately $28 million of credit commitment available for borrowing.
	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, 2014 are as follows (in thousands):
	2015		$	2,326
	2016			2,312
	2017			1,925
	2018			1,506
	2019			851
	Thereafter (1)			9,065
	Total minimum lease payments			17,985
	Less amount representing interest			(3,863	)
	Present value of future minimum lease payments		$	14,122
	-1	Amount includes $6.6 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_Geographi

Business Segment and Geographic Information	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Business Segment and Geographic Information	9	Business Segment and Geographic Information
	With our continued investment in our NxStage Kidney Care dialysis centers, effective with the first quarter of 2014, it was determined that the operations of NxStage Kidney Care should be presented separately. Prior to 2014, its operations were included within the Other category. We now 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 distribute our products in three markets: home, critical care and in-center. Prior period information has been updated to conform with the current presentation.
	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 in the home and critical care markets. The home market is devoted to the treatment of ESRD patients in the home or a home-like setting, 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. The results of our international business are included in the System One segment.
	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.
	Our Services segment includes revenues from dialysis services provided to patients at our NxStage Kidney Care dialysis centers.
	The remainder of our operations and financial information, included within the Other category, relates primarily 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.
	The accounting policies of our reportable segments are the same as those described in Note 2. 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			In-Center			Other			Services			Intersegment			Total
			One												Revenue
															Elimination
	Year Ended December 31, 2014
	Revenues from external customers		$	212,585		$	78,885		$	8,282		$	1,749		$	—		$	301,501
	Intersegment Revenues			846			—			—			—			(846	)		—
	Revenues			213,431			78,885			8,282			1,749			(846	)		301,501
	Segment profit (loss)			36,802			12,815			(56,878	)		(14,926	)		—			(22,187	)
	Depreciation and amortization			20,205			1,608			4,829			1,055			—			27,697
	Segment assets			127,212			29,613			136,041			16,860			—			309,726
	Year Ended December 31, 2013
	Revenues from external customers		$	176,756		$	81,852		$	4,469		$	352		$	—		$	263,429
	Intersegment Revenues			—			—			—			—			—			—
	Revenues			176,756			81,852			4,469			352			—			263,429
	Segment profit (loss)			24,036			16,447			(52,591	)		(5,690	)		—			(17,798	)
	Depreciation and amortization			18,041			1,389			5,283			135			—			24,848
	Segment assets			110,124			26,414			166,151			4,273			—			306,962
	Year Ended December 31, 2012
	Revenues from external customers		$	163,129		$	76,927		$	2,076		$	—		$	—		$	242,132
	Intersegment Revenues			—			—			—			—			—			—
	Revenues			163,129			76,927			2,076			—			—			242,132
	Segment profit (loss)			24,349			11,051			(45,388	)		(1,218	)		—			(11,206	)
	Depreciation and amortization			18,245			1,461			3,967			—			—			23,673
	Segment assets			80,041			20,582			211,326			—			—			311,949
	The following table presents a reconciliation of the total segment assets to total assets (in thousands):
			December 31,
			2014			2013
	Total segment assets		$	173,685		$	140,811
	Corporate assets:
	Cash and cash equivalents			52,884			84,134
	Accounts Receivable, net			277			397
	Property and equipment, net			17,269			17,000
	Intangible assets, net			14,370			17,194
	Goodwill			41,817			41,817
	Prepaid and other assets			9,424			5,609
	Total assets		$	309,726		$	306,962
	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,
			2014			2013			2012
	United States		$	45,501		$	26,082		$	20,967
	Mexico			12,689			10,578			3,949
	Other Americas			482			94			—
	Total Americas			58,672			36,754			24,916
	Germany			21,246			20,235			17,058
	Other Europe			7,774			8,530			4,447
	Total Europe			29,020			28,765			21,505
	Total		$	87,692		$	65,519		$	46,421
	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 to customers located 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,
			2014			2013			2012
	DaVita			21	%		21	%		21	%
	Fresenius			16	%		14	%		11	%
	Gambro			9	%		12	%		12	%
	Schein			8	%		10	%		11	%
	Sales to DaVita HealthCare Partners Inc. (DaVita) and Fresenius Medical Care (Fresenius) are in the System One segment. Sales to Gambro AB and Henry Schein, Inc. (Schein) are in the In-Center segment. All of Gambro’s sales of our products are to DaVita. A portion of Schein’s sales of our products are to DaVita.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	10	Commitments and Contingencies
	Purchase Commitments
	We have agreements with certain of our suppliers, primarily for the purchase of certain System One components and fluids along with needles for our In-Center segment that include minimum purchase commitments. As of December 31, 2014, we had a total of $62.3 million in minimum purchase commitments under these agreements over the next one 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 through 2018 to 2022, 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 $0.1million to $0.3 million per facility.
	Our foreign leased manufacturing facilities are subject to lease agreements with termination dates through December 2015 to 2018 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 executory 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 $3.8 million during 2014, $2.2 million during 2013 and $2.2 million during 2012.
	The future minimum rental payments as of December 31, 2014 under our operating leases are as follows (in thousands):
	2015		$	4,412
	2016			4,390
	2017			4,244
	2018			4,369
	2019			3,535
	Thereafter			8,523
			$	29,473
	Contingencies
	A civil complaint was filed against us on February 28, 2012 by Gambro Renal Products, Inc., or Gambro. The complaint alleged that we made false and misleading statements about our and Gambro’s allegedly competing products in the critical care market in commercial and promotional activities. The complaint also alleged that we wrongfully interfered with contractual and advantageous relationships of Gambro in its critical care business.
	Effective January 2, 2014, we and Gambro agreed to a settlement of this litigation without any admission of wrongdoing or liability. The settlement required us to pay a one-time cash payment to Gambro which was primarily offset by reimbursement from our insurance company. At the same time, we entered into a patent cross-license agreement and a distribution agreement amendment that amended the length and other terms of the agreement between us and Gambro. We recorded the settlement, reimbursement and consideration within general and administrative expense on the consolidated statements of comprehensive loss.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	11	Income Taxes
	The following is a summary of income (loss) before income taxes by geography (in thousands):
			Years Ended December 31,
			2014			2013			2012
	U.S.		$	(24,315	)	$	(20,613	)	$	(16,026	)
	Foreign			1,255			1,807			1,906
	Total		$	(23,060	)	$	(18,806	)	$	(14,120	)
	The components of the provision for (benefit from) income taxes are as follows (in thousands):
			Years Ended December 31,
			2014			2013			2012
	Current:
	U.S. - State		$	57		$	47		$	52
	Foreign			1,278			(76	)		1,357
	Total Current			1,335			(29	)		1,409
	Deferred:
	Foreign			(82	)		(216	)		(376	)
	Total Deferred			(82	)		(216	)		(376	)
	Total Provision (Benefit)		$	1,253		$	(245	)	$	1,033
	We recognized a provision for income taxes of $1.3 million during 2014, a benefit from income taxes of $0.2 million during 2013 and a provision for income taxes of $1.0 million during 2012. We recorded income tax expense during 2014, 2013 and 2012 for certain profitable foreign subsidiaries. The net benefit from income taxes recorded during 2013 includes the favorable conclusion of a foreign income tax audit which resulted in the recognition of a $1.2 million income tax benefit and a gain related to a foreign legislative change.
	A reconciliation of the U.S. federal statutory tax rate to the effective tax rate is as follows:
			Years Ended December 31,
			2014			2013			2012
	Federal statutory rate			34	%		34	%		34	%
	Stock compensation			2	%		(2.5	)%		(5.6	)%
	State income tax, net of federal tax benefit			1.9	%		3.2	%		2	%
	U.S. research credits			4.1	%		11.7	%		3.3	%
	Foreign income inclusion in the U.S.			(2.8	)%		(6.7	)%		(3.1	)%
	Valuation allowance			(39.7	)%		(40.2	)%		(31.4	)%
	Change in tax reserves			—	%		4	%		(5.6	)%
	Other, net			(4.9	)%		(2.2	)%		(0.9	)%
	Effective tax rate			(5.4	)%		1.3	%		(7.3	)%
	The 2013 effective tax rate included a $1.2 million income tax benefit from the favorable conclusion of a foreign income tax audit.
	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), the majority of which are non-current, are made up of the following (in thousands):
			December 31,
			2014			2013
	Deferred tax assets:
	Net operating loss carryforwards		$	114,131		$	108,772
	Tax credits			10,078			9,464
	Stock-based compensation			6,259			5,713
	Capitalized research and development			3,120			3,677
	Financing liabilities			6,281			5,007
	Other			6,092			2,199
	Total deferred tax assets			145,961			134,832
	Deferred tax liabilities:
	Fixed assets			(7,719	)		(5,079	)
	Intangible assets			(5,326	)		(6,509	)
	Other			(608	)		—
	Total deferred tax liabilities			(13,653	)		(11,588	)
	Net deferred tax assets before valuation allowance			132,308			123,244
	Less valuation allowance			(131,453	)		(122,353	)
	Net deferred tax assets		$	855		$	891
	As of December 31, 2014, we had U.S. federal and state net operating loss carryforwards of approximately $366 million and $187 million, respectively, available to offset future taxable income. A portion of the federal net operating loss, $54.2 million, and state net operating loss, $27.7 million, is attributable to excess tax deductions related to stock-based compensation. We will realize the benefit of these excess tax deductions through increases in shareholder’s equity in future periods when and if the losses are utilized to reduce future tax payments. The federal and state net operating loss carryforwards will expire between 2015 and 2034 if not utilized. Utilization of the net operating loss carryforwards may be subject to annual limitations due to the ownership percentage change limitations provided by the Internal Revenue Code Section 382 and similar state provisions. To date, we have not completed an analysis in accordance with §382. In the event of a deemed change in control under Internal Revenue Code Section 382, an annual limitation imposed on the utilization of net operating losses may result in the expiration of all or a portion of the net operating loss carryforwards. We also had federal and state research and development credit carryforwards of $7.0 million and $1.9 million, 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. As of December 31, 2014, we have not been subject to a federal income tax audit in the U.S.
	During 2014, the deferred tax valuation allowance increased by approximately $9.1 million, primarily as the result of increases to federal, state, and foreign net operating losses. 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. We believe that the future realization of these assets is not more likely than not given the expected future tax losses in these jurisdictions.
	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,
			2014			2013			2012
	Balance at beginning of the year		$	411		$	1,067		$	678
	Increase in unrecognized tax benefits current year			88			411			389
	Decrease in unrecognized tax benefits prior years			(110	)		—			—
	Reductions due to audit settlement			(42	)		(1,067	)		—
	Balance at end of year		$	347		$	411		$	1,067
	As of December 31, 2014 we had gross unrecognized tax benefits of $0.4 million that, if recognized, would result in a reduction of our effective tax rate. As of December 31, 2013 and 2012 we had gross unrecognized tax benefits of $0.5 million and $1.5 million, respectively, including interest and penalties of $0.1 million and $0.4 million.
	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, 2014, there were no significant undistributed earnings of foreign subsidiaries that were deemed permanently invested.

Stock_Plans_and_StockBased_Com

Stock Plans and Stock-Based Compensation	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Plans and Stock-Based Compensation	12	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 are fully vested for 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, 2014, 5.3 million shares remained available for future grant.
	We offer a corporate bonus plan for the benefit of our employees. Payout under the bonus plan is based on individual performance and the achievement of certain annual corporate financial performance metrics. Bonus awards are paid in cash or, at the discretion of the Compensation Committee of the Board, in shares of our common stock. The estimated payout under our bonus plan is recognized as compensation expense during the performance year and is classified as a liability, until settlement, on our consolidated balance sheet. The compensation expense associated with our bonus plan for the 2014, 2013 and 2012 performance years that has been or is expected to be paid in shares of our common stock has been classified as stock-based compensation expense.
	We also maintain the 2005 Employee Stock Purchase Plan (2005 Purchase Plan), which authorizes the issuance of up to 0.7 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, 2014, 0.1 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, 2014, and changes during the year then ended, is as follows:
	Stock Options		Shares			Weighted		Aggregate		Average
						Average		Intrinsic Value		Remaining
						Exercise				Contractual  Life
						Price
								(In thousands)		(In years)
	Outstanding at beginning of year			4,825,880		$	10.73
	Granted			997,459		$	14.35
	Exercised			(1,524,601	)	$	9.04
	Forfeited or expired			(196,313	)	$	15.17
	Outstanding at end of year			4,102,425		$	12.02	$	24,832		5.18
	Fully vested and exercisable			2,822,955		$	11.3	$	19,264		3.73
	Fully vested, exercisable and expected to vest			3,956,565		$	11.96	$	24,197		5.06
	The aggregate intrinsic value for stock options is calculated based on the market price of our common stock as of December 31, 2014, less the exercise price of the underlying awards, excluding out-of-the-money awards. The total fair value of options that vested during 2014, 2013 and 2012 was $4.9 million, $5.1 million and $5.1 million, respectively. The aggregate intrinsic value of options exercised during 2014, 2013 and 2012 was $9.2 million, $3.5 million and $8.8 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 2014, 2013 and 2012 was $5.80, $6.29 and $9.23 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,
			2014		2013	2012
	Expected life (in years)		4.40 to 5.00		4.50 to 4.70	4.5
	Risk-free interest rate		1.56% to 1.69%		0.75% to 1.04%	0.67% to 0.90%
	Expected stock price volatility		43% to 45%		62%	70%
	Expected dividend yield		—		—	—
	Restricted Stock
	The total fair value of restricted stock that vested was $3.2 million, $2.8 million and $3.7 million during 2014, 2013 and 2012, respectively. The weighted-average fair value of restricted stock granted during 2014, 2013 and 2012 was $14.35, $11.97 and $16.89 per unit, respectively. The following table summarizes the status of the unvested restricted stock:
			Shares			Weighted  Average		Aggregate		Weighted  Average
						Grant-date		Intrinsic  Value		Remaining
						Fair Value				Contractual Life
								(In thousands)		(In years)
	Unvested at December 31, 2013			734,221		$	14.72
	Granted			699,913		$	14.35
	Vested			(192,741	)	$	16.64
	Forfeited			(51,548	)	$	13.94
	Unvested at December 31, 2014			1,189,845		$	14.23	$	21,334		1.89
	The aggregate intrinsic value for restricted stock is calculated based on the market price of our common stock as of December 31, 2014.
	Employee Stock Purchase Plan
	The weighted-average fair value of stock purchase rights granted as part of the 2005 Purchase Plan during 2014, 2013 and 2012 was $1.46, $3.10 and $4.57 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,
			2014		2013	2012
	Expected life (in months)		6		6	6
	Risk-free interest rate		0.07% to 0.10%		0.09% to 0.12%	0.06% to 0.15%
	Expected stock price volatility		26.3% to 27.4%		20.1% to 33.6%	23.3% to 36.0%
	Expected dividend yield		—		—	—
	There were 70,899, 75,301 and 56,691 shares issued under the 2005 Purchase Plan during 2014, 2013 and 2012, respectively, which resulted in share-based compensation expense of $0.1 million, $0.1 million, and $0.2 million in 2014, 2013 and 2012, respectively.
	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,
			2014			2013		2012
	Cost of revenues		$	1,212		$	918	$	1,168
	Selling and marketing			4,442			3,171		4,186
	Research and development			1,726			1,331		1,372
	General and administrative			5,501			3,218		4,677
	Total stock-based compensation expense		$	12,881		$	8,638	$	11,403
	As of December 31, 2014, approximately $19 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 2.6 years.
	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 $1.7 million and $1.8 million at December 31, 2014 and 2013, respectively, as other long-term liabilities for costs associated with these plans. The expense recorded in connection with these plans was not significant during 2014, 2013 and 2012.

Employee_Benefit_Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Employee Benefit Plan	13	Employee Benefit 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 $1.7 million, $1.5 million and $1.3 million to the 401(k) Plan during 2014, 2013 and 2012, respectively.

Stockholders_Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Stockholders' Equity	14	Stockholders’ Equity
	We received 196,378, 34,311 and 32,310 shares of common stock that were surrendered in payment for the exercise of stock options during 2014, 2013 and 2012, respectively.
	During 2012, we repaid in full all principal and interest in the aggregate amount of $45.2 million under our term loan and security agreement with Asahi through the issuance of 2,456,246 shares of our common stock, which, after the retention by us of 28,351 shares for the payment of certain minimum withholding taxes, resulted in a net issuance to Asahi of 2,427,895 shares.
	In connection with the sale of our common stock in a private placement during 2008 we issued warrants to purchase 1,900,000 shares of our common stock. These warrants had an exercise price of $5.50 per share and contained a net share settlement feature. As of December 31, 2013, all warrants had been exercised or had expired.

Business_Combination

Business Combination	12 Months Ended
	Dec. 31, 2014
Business Combinations [Abstract]
Business Combination	15	Business Combination
	During 2013, we acquired substantially all of the System One assets of Kimal PLC, or Kimal, a distributor of our products in the United Kingdom. The acquisition was consistent with our move to a direct sales model in the United Kingdom. The aggregate purchase price of $4.0 million include cash payments of $0.1 million and $2.2 million paid in 2014 and 2013, respectively, the forgiveness of a capital lease liability due from Kimal of $1.5 million, contingent consideration of $0.5 million paid in 2014 and offset by the reclassification of deferred revenues of $0.3 million, net of related deferred cost of revenues, associated with sales of equipment to Kimal prior to January 1, 2011.
	The following table presents the allocation of the purchase price to the estimated fair value of the assets acquired (in thousands):
	Assets purchased:
	Inventory		$	523
	Field Equipment			3,298
	Customer relationships			170
	Assets acquired		$	3,991
	The fair values of inventory and field equipment noted above approximated their net book value at the time of acquisition. The customer relationships were valued using the multi-period excess-earnings method, a form of the income approach, using certain significant unobservable inputs (classified as level 3 in the fair value hierarchy), namely, a discount rate of 11.5%, projected future cash flows, and patient growth rates.

Derivative_Instruments_and_Hed

Derivative Instruments and Hedging	12 Months Ended
	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging	16	Derivative Instruments and Hedging
	We operate a manufacturing and service facility in Mexico and we purchase materials and pay our employees at that facility in pesos, and as such, we are potentially exposed to adverse as well as beneficial movements in foreign currency exchange rates. We enter into foreign exchange forward contracts to minimize the impact of foreign currency exchange rate fluctuations on these peso denominated expenses. These contracts have a duration 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 $12.5 million and $10.4 million at December 31, 2014 and December 31, 2013, respectively. The fair value of these contracts was recorded on the balance sheet within prepaid expenses and other current assets or other current liabilities depending on the gain (loss) position. The fair value of these contracts was a liability of $1.3 million and $0.2 million at December 31, 2014 and December 31, 2013, respectively.
	Gains or losses related to hedge ineffectiveness recognized in earnings were not material during 2014 or 2013. 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)			Gain (Loss)			Classification within the
			Recognized in OCI			Reclassified from			Condensed Consolidated
			(Effective Portion)			OCI into Income			Statement of
						(Effective Portion)			Comprehensive Loss
	Year Ended December 31, 2014		$	(1,223	)	$	(258	)	Cost of revenues
	Year Ended December 31, 2013		$	144		$	656		Cost of revenues
	Year Ended December 31, 2012		$	498		$	109		Cost of revenues

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive (Loss) Income	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Accumulated Other Comprehensive (Loss) Income	17	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)			Other (2)			Total
			on derivative
			instruments
	Balance, net of tax, as of December 31, 2011		$	—		$	(68	)	$	(68	)
	Other comprehensive income before reclassifications			498			149			647
	Gain reclassified to earnings (1)			(109	)		—			(109	)
	Total other comprehensive income			389			149			538
	Balance, net of tax, as of December 31, 2012		$	389		$	81		$	470
	Other comprehensive income before reclassifications			144			254			398
	Gain reclassified to earnings (1)			(656	)		—			(656	)
	Total other comprehensive income (loss)			(512	)		254			(258	)
	Balance, net of tax, as of December 31, 2013		$	(123	)	$	335		$	212
	Other comprehensive loss before reclassifications			(1,223	)		(1,439	)		(2,662	)
	Loss reclassified to earnings (1)			258			—			258
	Total other comprehensive loss			(965	)		(1,439	)		(2,404	)
	Balance, net of tax, as of December 31, 2014		$	(1,088	)	$	(1,104	)	$	(2,192	)
	-1	Reclassifications of gains (losses) on derivative instruments are included in cost of revenues on the consolidated statement of comprehensive loss. See Note 16 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, 2014
Fair Value Disclosures [Abstract]
Fair Value Measurements	18	Fair Value Measurements
	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, 2014		Quoted Prices in			Significant Other		Significant		Total Fair Value
			Active  Markets for			Observable Inputs		Unobservable  Inputs
			Identical Assets			(Level 2)		(Level 3)
			(Level 1)
	Assets
	Money market funds(1)		$	39,779		$	—	$	—	$	39,779
	Liabilities
	Foreign exchange forward contracts(2)		$	—		$	1,265	$	—	$	1,265
	December 31, 2013		Quoted Prices in			Significant Other		Significant		Total Fair Value
			Active Markets for			Observable Inputs		Unobservable Inputs
			Identical Assets			(Level 2)		(Level 3)
			(Level 1)
	Assets
	Money market funds(1)		$	69,779		$	—	$	—	$	69,779
	Foreign exchange forward contracts(2)			—			34		—		34
	Liabilities
	Foreign exchange forward contracts(2)		$	—		$	192	$	—	$	192
	Contingent consideration liability(3)			—			—		540		540
	-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 other current liabilities depending on the gain (loss) position.
	-3	Net present value of expected payments under contingent consideration liability are reported in accrued expenses.
	We did not have any transfers between Level 1 and Level 2 during the twelve months ended December 31, 2014 or 2013.
	The following table presents the rollforward of the contingent consideration liability classified as Level 3 within the value hierarchy (in thousands):
	Balance at December 31, 2013		$	540
	Less Payments made			(540	)
	Balance at December 31, 2014		$	—
	Our contingent consideration liability related to deferred payments made in January and April 2014 in connection with our acquisition of substantially all of the System One assets of Kimal PLC, a distributor of our products in the United Kingdom, on April 2, 2013. The liability recorded at December 31, 2013 was measured using probability weighted discounted cash flow method and includes certain significant unobservable inputs, namely, a discount rate of 11.5% and patient growth rates.
	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.
	The carrying amount of our long-term debt approximates fair value at December 31, 2014. 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, 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.

Supplemental_Cash_Flow_Informa

Supplemental Cash Flow Information	12 Months Ended
	Dec. 31, 2014
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	19	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,
			2014		2013		2012
	Supplemental Disclosures:
	Cash paid for interest		$	671	$	549	$	1,457
	Cash paid for taxes			903		1,181		586
	Noncash Investing and Financing Activities:
	Transfers from inventory to field equipment		$	25,370	$	13,827	$	12,172
	Transfers from field equipment to deferred cost of revenues			13,110		10,260		10,360
	Payment of Corporate Bonus Plan in common stock			—		1,034		878
	Market value of shares received in payment for exercise of stock options			3,026		412		513
	Construction-in-process financed by construction liability			4,898		3,568		8,343
	Settlement of debt through the issuance of common stock			—		—		45,219
	Leasehold improvements paid by the landlord			—		—		4,300
	Property and equipment acquired under capital lease			76		745		1,615
	Acquisition of business			—		1,757		—
	Increase in deferred revenues related to the new manufacturing facility in Germany			3,608		—		6,124
	Deferred revenues and deferred costs related to acquiree recorded as a reduction of consideration paid			—		335		—

Quarterly_Financial_Data_Unaud

Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data (Unaudited)	20	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,
			2014			2014			2014			2014
	Revenues		$	72,221		$	74,083		$	75,286		$	79,911
	Gross profit			28,934			27,530			28,587			30,852
	Loss from operations			(4,789	)		(6,651	)		(6,274	)		(4,473	)
	Net loss attributable to stockholders of NxStage Medical, Inc.			(5,275	)		(7,113	)		(6,706	)		(4,852	)
	Net loss per share, basic and diluted		$	(0.09	)	$	(0.12	)	$	(0.11	)	$	(0.08	)
			Three Months Ended
			March 31,			June 30,			September 30,			December 31,
			2013			2013			2013			2013
	Revenues		$	61,644		$	65,462		$	66,873		$	69,450
	Gross profit			24,000			25,087			25,528			27,888
	Loss from operations			(4,536	)		(4,271	)		(4,413	)		(4,578	)
	Net loss attributable to stockholders of NxStage Medical, Inc.			(4,994	)		(3,405	)		(4,986	)		(5,176	)
	Net loss per share, basic and diluted		$	(0.08	)	$	(0.06	)	$	(0.08	)	$	(0.08	)

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Principles of Consolidation and Basis of Presentation	Principles of Consolidation and Basis of Presentation
	The accompanying consolidated financial statements include the accounts of NxStage Medical, Inc. and our wholly-owned and majority-owned subsidiaries. All material intercompany transactions and balances have been eliminated in consolidation.
Use of Estimates	Use of Estimates
	The preparation of our consolidated financial statements in conformity with GAAP requires our management to make estimates and assumptions that affect reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
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 market 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.
	System One Segment
	We derive revenue in the home market from the sales of hemodialysis therapy to customers in which the customer either purchases or rents the System One and/or PureFlow SL hardware and purchases a specified number of disposable products and service.
	For customers that purchase the System One and PureFlow SL hardware, in the U.S. 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 fees received from equipment sale 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 deferred and amortized over the same expected period as the related revenue. Disposable products revenue is recognized on a monthly basis upon delivery.
	Under the rental 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. Some of our distribution contracts for the In-Center segment contain minimum volume commitments with negotiated pricing discounts at different volume tiers. Each agreement may be canceled upon a material breach, subject to certain curing rights, and in many instances minimum volume commitments can be reduced or eliminated upon certain events.
	Services Segment
	Revenues in our Services segment are derived from dialysis care services provided to patients at our recently opened 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 (expense) income, 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 market value.
Concentration of Credit Risk	Concentration of Credit Risk
	Financial instruments that potentially subject us to concentrations of credit risk consist principally of 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. Two customers represented 18% and 16% of accounts receivable at December 31, 2014 and one customer represented 19% of accounts receivable at December 31, 2013. 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, 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		Provision		Write-offs			Balance at End of
		Beginning of Year		(Recoveries)					Year
	December 31, 2014	$	321	$	219	$	(115	)	$	425
	December 31, 2013	$	424	$	47	$	(150	)	$	321
	December 31, 2012	$	510	$	—	$	(86	)	$	424
	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 Measures	Fair Value Measures
	Certain financial and non financial assets and liabilities recorded at fair value have been classified as Level 1, 2 or 3 within the fair value hierarchy as described in the accounting standard. Fair values determined by Level 1 inputs utilize quoted prices (unadjusted) in active markets for identical assets or liabilities that we have the ability to access. Fair values determined by Level 2 inputs utilize data points that are observable such as quoted prices, interest rates and yield curves for similar instruments and model-derived valuations whose inputs are observable. Fair values determined by Level 3 inputs utilize unobservable data points for 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.
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 record a provision for any excess or obsolete inventory when warranted based on remaining shelf-life and estimated future demand. 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 life 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, 2014 and 2013 primarily represents the costs of building, machinery, equipment under installation and software and computer costs.
	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
	Manufacturing equipment and tooling	3 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 computed using the straight-line method over the estimated economic lives of the respective intangible assets, ranging from eight to fourteen years. Long-lived assets, including intangible assets, are tested for recoverability whenever events or circumstances indicate that their carrying value may not be recoverable. The amount of impairment, if any, is measured based on fair value, which is determined using estimated discounted cash flows to be generated from such assets or group of assets. During 2014, 2013 and 2012, no such impairment was recognized. 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 fair value of the related net assets at the date of acquisition. We test goodwill at least annually for impairment, or more frequently when events or changes in circumstances indicate that the goodwill might be impaired. This impairment test is performed annually during the fourth quarter. 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. 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. Our reporting units with goodwill are our System One and In-center operating segments. During both 2014 and 2012, we utilized the qualitative assessment and concluded that it was more likely than not that the fair value of our reporting units was greater than their carrying value. During 2013, we utilized the quantitative assessment and concluded the fair value of the reporting units exceeds their carrying value, indicating that goodwill was not impaired. We estimated the fair value of our reporting units using a discounted cash flow approach which involves significant judgment with respect to future revenue growth, operating income, capital expenditures, changes in working capital use and the selection of a discount rate.
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 generally 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. The following is a rollforward of our warranty accrual (in thousands):
	Year Ended	Balance at		Provision		Usage			Balance at End of
		Beginning of Year							Year
	December 31, 2014	$	297	$	441	$	(451	)	$	287
	December 31, 2013	$	324	$	412	$	(439	)	$	297
	December 31, 2012	$	380	$	540	$	(596	)	$	324
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 have accumulated significant losses since our inception in 1998. Utilization of the net operating losses may be subject to limitations and certain tax years in the respective tax jurisdictions remain open to examination.
Subsequent Events	Subsequent Events
	Events occurring subsequent to December 31, 2014 have been evaluated for potential recognition or disclosure in the consolidated financial statements.
Recent Accounting Pronouncements	Recent Accounting Pronouncements
	Effective January 1, 2014, we adopted Financial Accounting Standards Board (FASB) Accounting Standards Update (ASU) No. 2013-11, “Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists,” which impacts the presentation of unrecognized tax benefits on the statement of financial position. As a result, unrecognized tax benefits are presented as a reduction to a deferred tax asset for a net operating loss carryforward, a similar tax loss, or a tax credit carryforward. To the extent the tax benefit is not available at the reporting date under the governing tax law or if we do not intend to use the deferred tax asset for such purpose, the unrecognized tax benefit is presented as a liability and not combined with deferred tax assets. The adoption of this standard did not impact our condensed consolidated financial statements, as our practice was consistent with this standard prior to its effective date.
	In May 2014, the FASB issued ASU No. 2014-09, “Revenue from Contracts with Customers,” which provides guidance for revenue recognition. The standard’s core principle is that a company will recognize revenue when it 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. The new guidance is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. Early application is not permitted. We are currently assessing the potential impact the adoption of this standard will have on our financial statements.
	In August 2014, the FASB issued ASU No. 2014-15, “Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern” (“ASU 2014-15”), which expands upon principles that are currently in U.S. auditing standards by providing guidance on management’s responsibility in evaluating whether there is substantial doubt about a company’s ability to continue as a going concern and by providing related footnote disclosure requirements. The new guidance is effective for the annual period ending after December 15, 2016, and for annual periods and interim periods thereafter. Early adoption is permitted. We are currently evaluating the impact of this update but it is not expected to have a material impact on our financial statement disclosures.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Allowance for Doubtful Accounts	Activity related to allowance for doubtful accounts consisted of the following (in thousands):
	Year Ended	Balance at		Provision		Write-offs			Balance at End of
		Beginning of Year		(Recoveries)					Year
	December 31, 2014	$	321	$	219	$	(115	)	$	425
	December 31, 2013	$	424	$	47	$	(150	)	$	321
	December 31, 2012	$	510	$	—	$	(86	)	$	424
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
	Manufacturing equipment and tooling	3 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
Schedule of Rollforward of Warranty Accrual	The following is a rollforward of our warranty accrual (in thousands):
	Year Ended	Balance at		Provision		Usage			Balance at End of
		Beginning of Year							Year
	December 31, 2014	$	297	$	441	$	(451	)	$	287
	December 31, 2013	$	324	$	412	$	(439	)	$	297
	December 31, 2012	$	380	$	540	$	(596	)	$	324

Inventory_Tables

Inventory (Tables)	12 Months Ended
	Dec. 31, 2014
Inventory Disclosure [Abstract]
Components of Inventory	The components of inventory are as follows (in thousands):
		December 31,
		2014		2013
	Purchased components	$	19,238	$	15,946
	Work in process		9,981		10,762
	Finished goods		16,182		11,093
		$	45,401	$	37,801

Property_and_Equipment_Field_E1

Property and Equipment, Field Equipment and Deferred Cost of Revenues (Tables)	12 Months Ended
	Dec. 31, 2014
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,
		2014			2013
	Manufacturing equipment and tooling	$	34,621		$	24,963
	Leasehold improvements		18,485			11,883
	Computer and office equipment		8,935			4,132
	Molds		5,377			3,817
	Furniture		2,410			1,712
	Buildings		8,907			10,005
	Land		1,110			1,258
	Construction-in-process		14,609			16,500
			94,454			74,270
	Less accumulated depreciation		(27,880	)		(21,792	)
	Property and equipment, net	$	66,574		$	52,478
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,
		2014
	Manufacturing facility in Germany	$	22,750
	Other assets subject to capital leases		2,438
	Less accumulated depreciation		(2,905	)
	Assets subject to capital leases, net	$	22,283
Components of Field Equipment, Net	The components of field equipment, net are as follows (in thousands):
		December 31,
		2014			2013
	Field equipment	$	61,132		$	49,695
	Less accumulated depreciation		(40,014	)		(36,654	)
	Field equipment, net	$	21,118		$	13,041

Intangible_Assets_Tables

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Summary of Intangible Assets	The components of intangible assets, net are as follows (in thousands):
		December 31, 2014					December 31, 2013					Estimated
												Useful
		Cost		Accumulated			Cost		Accumulated			Life
				Amortization					Amortization
	Bloodline, needle and other patented and unpatented technology	$	6,200	$	(5,619	)	$	6,200	$	(4,844	)		8 years
	Trade names		2,300		(1,191	)		2,300		(1,026	)		14 years
	Customer relationships		26,175		(13,495	)		26,185		(11,621	)		10/14 years
	Intangible assets, net	$	34,675	$	(20,305	)	$	34,685	$	(17,491	)
Estimated Future Aggregated Amortization Expense for Intangible Assets	The estimated future aggregated amortization expense for intangible assets as of December 31, 2014 is as follows (in thousands):
	2015	$	2,621
	2016		2,040
	2017		2,040
	2018		2,040
	2019		2,040
	Thereafter		3,589
		$	14,370

Net_Loss_per_Share_Tables

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2014
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,
		2014		2013		2012
	Options to purchase common stock		876		1,013		1,602
	Unvested restricted stock		236		152		196
	Warrants to purchase common stock		—		—		921
	Total		1,112		1,165		2,719

Accrued_Expenses_Other_Current1

Accrued Expenses, Other Current Liabilities, and Other Long Term Liabilities (Tables)	12 Months Ended
	Dec. 31, 2014
Payables and Accruals [Abstract]
Components of Accrued Expenses	The components of accrued expenses are as follows (in thousands):
		December 31,
		2014		2013
	Payroll, compensation and related benefits	$	12,346	$	9,041
	Distribution expenses		3,069		2,762
	General and administrative expenses		3,075		2,207
	Audit, legal, and consulting fees		1,394		2,725
	Other		4,769		4,290
	Total	$	24,653	$	21,025
Components of Other Current liabilities	The components of other current liabilities are as follows (in thousands):
		December 31,
		2014		2013
	Deferred revenue, current portion	$	2,195	$	—
	Capital lease obligations		2,246		1,471
	Other		1,724		399
	Total	$	6,165	$	1,870
Schedule of Other Long-term Liabilities	The components of other long term liabilities are as follows (in thousands):
		December 31,
		2014		2013
	Capital lease obligations	$	11,876	$	14,133
	Lease incentive obligations		4,569		3,589
	Benefit plan obligations		1,745		1,770
	Other		1,434		781
	Total	$	19,624	$	20,273

Debt_and_Capital_Lease_Obligat1

Debt and Capital Lease Obligations (Tables)	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Schedule of Future Minimum Payments under Capital Leases	Approximate future minimum payments under our capital leases as of December 31, 2014 are as follows (in thousands):
	2015		$	2,326
	2016			2,312
	2017			1,925
	2018			1,506
	2019			851
	Thereafter (1)			9,065
	Total minimum lease payments			17,985
	Less amount representing interest			(3,863	)
	Present value of future minimum lease payments		$	14,122
	-1	Amount includes $6.6 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_Geographi1

Business Segment and Geographic Information (Tables)	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Summary of Operating Performance of Reportable Segments	The following summarizes the operating performance of our reportable segments (in thousands):
		System			In-Center			Other			Services			Intersegment			Total
		One												Revenue
														Elimination
	Year Ended December 31, 2014
	Revenues from external customers	$	212,585		$	78,885		$	8,282		$	1,749		$	—		$	301,501
	Intersegment Revenues		846			—			—			—			(846	)		—
	Revenues		213,431			78,885			8,282			1,749			(846	)		301,501
	Segment profit (loss)		36,802			12,815			(56,878	)		(14,926	)		—			(22,187	)
	Depreciation and amortization		20,205			1,608			4,829			1,055			—			27,697
	Segment assets		127,212			29,613			136,041			16,860			—			309,726
	Year Ended December 31, 2013
	Revenues from external customers	$	176,756		$	81,852		$	4,469		$	352		$	—		$	263,429
	Intersegment Revenues		—			—			—			—			—			—
	Revenues		176,756			81,852			4,469			352			—			263,429
	Segment profit (loss)		24,036			16,447			(52,591	)		(5,690	)		—			(17,798	)
	Depreciation and amortization		18,041			1,389			5,283			135			—			24,848
	Segment assets		110,124			26,414			166,151			4,273			—			306,962
	Year Ended December 31, 2012
	Revenues from external customers	$	163,129		$	76,927		$	2,076		$	—		$	—		$	242,132
	Intersegment Revenues		—			—			—			—			—			—
	Revenues		163,129			76,927			2,076			—			—			242,132
	Segment profit (loss)		24,349			11,051			(45,388	)		(1,218	)		—			(11,206	)
	Depreciation and amortization		18,245			1,461			3,967			—			—			23,673
	Segment assets		80,041			20,582			211,326			—			—			311,949
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,
		2014			2013
	Total segment assets	$	173,685		$	140,811
	Corporate assets:
	Cash and cash equivalents		52,884			84,134
	Accounts Receivable, net		277			397
	Property and equipment, net		17,269			17,000
	Intangible assets, net		14,370			17,194
	Goodwill		41,817			41,817
	Prepaid and other assets		9,424			5,609
	Total assets	$	309,726		$	306,962
Total Long-Lived Tangible Assets by Geographic Area	The following table presents total long-lived tangible assets by geographic area (in thousands):
		December 31,
		2014			2013			2012
	United States	$	45,501		$	26,082		$	20,967
	Mexico		12,689			10,578			3,949
	Other Americas		482			94			—
	Total Americas		58,672			36,754			24,916
	Germany		21,246			20,235			17,058
	Other Europe		7,774			8,530			4,447
	Total Europe		29,020			28,765			21,505
	Total	$	87,692		$	65,519		$	46,421
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,
		2014			2013			2012
	DaVita		21	%		21	%		21	%
	Fresenius		16	%		14	%		11	%
	Gambro		9	%		12	%		12	%
	Schein		8	%		10	%		11	%

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Future Minimum Rental Payments under Operating Leases	The future minimum rental payments as of December 31, 2014 under our operating leases are as follows (in thousands):
	2015	$	4,412
	2016		4,390
	2017		4,244
	2018		4,369
	2019		3,535
	Thereafter		8,523
		$	29,473

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
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,
		2014			2013			2012
	U.S.	$	(24,315	)	$	(20,613	)	$	(16,026	)
	Foreign		1,255			1,807			1,906
	Total	$	(23,060	)	$	(18,806	)	$	(14,120	)
Components of Provision for (Benefit from) Income Taxes	The components of the provision for (benefit from) income taxes are as follows (in thousands):
		Years Ended December 31,
		2014			2013			2012
	Current:
	U.S. - State	$	57		$	47		$	52
	Foreign		1,278			(76	)		1,357
	Total Current		1,335			(29	)		1,409
	Deferred:
	Foreign		(82	)		(216	)		(376	)
	Total Deferred		(82	)		(216	)		(376	)
	Total Provision (Benefit)	$	1,253		$	(245	)	$	1,033
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,
		2014			2013			2012
	Federal statutory rate		34	%		34	%		34	%
	Stock compensation		2	%		(2.5	)%		(5.6	)%
	State income tax, net of federal tax benefit		1.9	%		3.2	%		2	%
	U.S. research credits		4.1	%		11.7	%		3.3	%
	Foreign income inclusion in the U.S.		(2.8	)%		(6.7	)%		(3.1	)%
	Valuation allowance		(39.7	)%		(40.2	)%		(31.4	)%
	Change in tax reserves		—	%		4	%		(5.6	)%
	Other, net		(4.9	)%		(2.2	)%		(0.9	)%
	Effective tax rate		(5.4	)%		1.3	%		(7.3	)%
Deferred Tax Assets (Liabilities)	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), the majority of which are non-current, are made up of the following (in thousands):
		December 31,
		2014			2013
	Deferred tax assets:
	Net operating loss carryforwards	$	114,131		$	108,772
	Tax credits		10,078			9,464
	Stock-based compensation		6,259			5,713
	Capitalized research and development		3,120			3,677
	Financing liabilities		6,281			5,007
	Other		6,092			2,199
	Total deferred tax assets		145,961			134,832
	Deferred tax liabilities:
	Fixed assets		(7,719	)		(5,079	)
	Intangible assets		(5,326	)		(6,509	)
	Other		(608	)		—
	Total deferred tax liabilities		(13,653	)		(11,588	)
	Net deferred tax assets before valuation allowance		132,308			123,244
	Less valuation allowance		(131,453	)		(122,353	)
	Net deferred tax assets	$	855		$	891
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,
		2014			2013			2012
	Balance at beginning of the year	$	411		$	1,067		$	678
	Increase in unrecognized tax benefits current year		88			411			389
	Decrease in unrecognized tax benefits prior years		(110	)		—			—
	Reductions due to audit settlement		(42	)		(1,067	)		—
	Balance at end of year	$	347		$	411		$	1,067

Stock_Plans_and_StockBased_Com1

Stock Plans and Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2014
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, 2014, and changes during the year then ended, is as follows:
	Stock Options	Shares			Weighted		Aggregate		Average
					Average		Intrinsic Value		Remaining
					Exercise				Contractual  Life
					Price
							(In thousands)		(In years)
	Outstanding at beginning of year		4,825,880		$	10.73
	Granted		997,459		$	14.35
	Exercised		(1,524,601	)	$	9.04
	Forfeited or expired		(196,313	)	$	15.17
	Outstanding at end of year		4,102,425		$	12.02	$	24,832		5.18
	Fully vested and exercisable		2,822,955		$	11.3	$	19,264		3.73
	Fully vested, exercisable and expected to vest		3,956,565		$	11.96	$	24,197		5.06
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,
		2014		2013	2012
	Expected life (in years)	4.40 to 5.00		4.50 to 4.70	4.5
	Risk-free interest rate	1.56% to 1.69%		0.75% to 1.04%	0.67% to 0.90%
	Expected stock price volatility	43% to 45%		62%	70%
	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		Aggregate		Weighted  Average
					Grant-date		Intrinsic  Value		Remaining
					Fair Value				Contractual Life
							(In thousands)		(In years)
	Unvested at December 31, 2013		734,221		$	14.72
	Granted		699,913		$	14.35
	Vested		(192,741	)	$	16.64
	Forfeited		(51,548	)	$	13.94
	Unvested at December 31, 2014		1,189,845		$	14.23	$	21,334		1.89
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,
		2014		2013	2012
	Expected life (in months)	6		6	6
	Risk-free interest rate	0.07% to 0.10%		0.09% to 0.12%	0.06% to 0.15%
	Expected stock price volatility	26.3% to 27.4%		20.1% to 33.6%	23.3% to 36.0%
	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,
		2014			2013		2012
	Cost of revenues	$	1,212		$	918	$	1,168
	Selling and marketing		4,442			3,171		4,186
	Research and development		1,726			1,331		1,372
	General and administrative		5,501			3,218		4,677
	Total stock-based compensation expense	$	12,881		$	8,638	$	11,403

Business_Combination_Tables

Business Combination (Tables)	12 Months Ended
	Dec. 31, 2014
Business Combinations [Abstract]
Allocation of Purchase Price to Estimated Fair Value of Assets Acquired	The following table presents the allocation of the purchase price to the estimated fair value of the assets acquired (in thousands):
	Assets purchased:
	Inventory	$	523
	Field Equipment		3,298
	Customer relationships		170
	Assets acquired	$	3,991

Derivative_Instruments_and_Hed1

Derivative Instruments and Hedging (Tables)	12 Months Ended
	Dec. 31, 2014
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)			Gain (Loss)			Classification within the
		Recognized in OCI			Reclassified from			Condensed Consolidated
		(Effective Portion)			OCI into Income			Statement of
					(Effective Portion)			Comprehensive Loss
	Year Ended December 31, 2014	$	(1,223	)	$	(258	)	Cost of revenues
	Year Ended December 31, 2013	$	144		$	656		Cost of revenues
	Year Ended December 31, 2012	$	498		$	109		Cost of revenues

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive (Loss) Income (Tables)	12 Months Ended
	Dec. 31, 2014
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)			Other (2)			Total
			on derivative
			instruments
	Balance, net of tax, as of December 31, 2011		$	—		$	(68	)	$	(68	)
	Other comprehensive income before reclassifications			498			149			647
	Gain reclassified to earnings (1)			(109	)		—			(109	)
	Total other comprehensive income			389			149			538
	Balance, net of tax, as of December 31, 2012		$	389		$	81		$	470
	Other comprehensive income before reclassifications			144			254			398
	Gain reclassified to earnings (1)			(656	)		—			(656	)
	Total other comprehensive income (loss)			(512	)		254			(258	)
	Balance, net of tax, as of December 31, 2013		$	(123	)	$	335		$	212
	Other comprehensive loss before reclassifications			(1,223	)		(1,439	)		(2,662	)
	Loss reclassified to earnings (1)			258			—			258
	Total other comprehensive loss			(965	)		(1,439	)		(2,404	)
	Balance, net of tax, as of December 31, 2014		$	(1,088	)	$	(1,104	)	$	(2,192	)
	-1	Reclassifications of gains (losses) on derivative instruments are included in cost of revenues on the consolidated statement of comprehensive loss. See Note 16 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, 2014
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, 2014		Quoted Prices in			Significant Other		Significant		Total Fair Value
			Active  Markets for			Observable Inputs		Unobservable  Inputs
			Identical Assets			(Level 2)		(Level 3)
			(Level 1)
	Assets
	Money market funds(1)		$	39,779		$	—	$	—	$	39,779
	Liabilities
	Foreign exchange forward contracts(2)		$	—		$	1,265	$	—	$	1,265
	December 31, 2013		Quoted Prices in			Significant Other		Significant		Total Fair Value
			Active Markets for			Observable Inputs		Unobservable Inputs
			Identical Assets			(Level 2)		(Level 3)
			(Level 1)
	Assets
	Money market funds(1)		$	69,779		$	—	$	—	$	69,779
	Foreign exchange forward contracts(2)			—			34		—		34
	Liabilities
	Foreign exchange forward contracts(2)		$	—		$	192	$	—	$	192
	Contingent consideration liability(3)			—			—		540		540
	-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 other current liabilities depending on the gain (loss) position.
	-3	Net present value of expected payments under contingent consideration liability are reported in accrued expenses.
Roll Forward of Contingent Consideration Liability Classified as Level 3 within Value Hierarchy	The following table presents the rollforward of the contingent consideration liability classified as Level 3 within the value hierarchy (in thousands):
	Balance at December 31, 2013		$	540
	Less Payments made			(540	)
	Balance at December 31, 2014		$	—

Supplemental_Cash_Flow_Informa1

Supplemental Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2014
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,
		2014		2013		2012
	Supplemental Disclosures:
	Cash paid for interest	$	671	$	549	$	1,457
	Cash paid for taxes		903		1,181		586
	Noncash Investing and Financing Activities:
	Transfers from inventory to field equipment	$	25,370	$	13,827	$	12,172
	Transfers from field equipment to deferred cost of revenues		13,110		10,260		10,360
	Payment of Corporate Bonus Plan in common stock		—		1,034		878
	Market value of shares received in payment for exercise of stock options		3,026		412		513
	Construction-in-process financed by construction liability		4,898		3,568		8,343
	Settlement of debt through the issuance of common stock		—		—		45,219
	Leasehold improvements paid by the landlord		—		—		4,300
	Property and equipment acquired under capital lease		76		745		1,615
	Acquisition of business		—		1,757		—
	Increase in deferred revenues related to the new manufacturing facility in Germany		3,608		—		6,124
	Deferred revenues and deferred costs related to acquiree recorded as a reduction of consideration paid		—		335		—

Quarterly_Financial_Data_Unaud1

Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
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,
		2014			2014			2014			2014
	Revenues	$	72,221		$	74,083		$	75,286		$	79,911
	Gross profit		28,934			27,530			28,587			30,852
	Loss from operations		(4,789	)		(6,651	)		(6,274	)		(4,473	)
	Net loss attributable to stockholders of NxStage Medical, Inc.		(5,275	)		(7,113	)		(6,706	)		(4,852	)
	Net loss per share, basic and diluted	$	(0.09	)	$	(0.12	)	$	(0.11	)	$	(0.08	)
		Three Months Ended
		March 31,			June 30,			September 30,			December 31,
		2013			2013			2013			2013
	Revenues	$	61,644		$	65,462		$	66,873		$	69,450
	Gross profit		24,000			25,087			25,528			27,888
	Loss from operations		(4,536	)		(4,271	)		(4,413	)		(4,578	)
	Net loss attributable to stockholders of NxStage Medical, Inc.		(4,994	)		(3,405	)		(4,986	)		(5,176	)
	Net loss per share, basic and diluted	$	(0.08	)	$	(0.06	)	$	(0.08	)	$	(0.08	)

Summary_of_Significant_Account3

Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Line Items]
Impairment charges	$0	$0	$0
Goodwill impairment	0	0	0
Cash dividend	$0
Percentage of tax benefit realized upon ultimate settlement with taxing authority	50.00%
Minimum [Member]
Accounting Policies [Line Items]
Finite-Lived Intangible Assets, Estimated Useful Life	8 years
Maximum [Member]
Accounting Policies [Line Items]
Finite-Lived Intangible Assets, Estimated Useful Life	14 years
Major Customer One [Member] | Customer Concentration Risk [Member] | Accounts Receivable [Member]
Accounting Policies [Line Items]
Percentage of accounts receivable	18.00%	19.00%
Major Customer Two [Member] | Customer Concentration Risk [Member] | Accounts Receivable [Member]
Accounting Policies [Line Items]
Percentage of accounts receivable	16.00%

Summary_of_Significant_Account4

Summary of Significant Accounting Policies - Allowance for Doubtful Accounts (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Abstract]
Balance at Beginning of Year	$321	$424	$510
Provision (Recoveries)	219	47
Write-offs	-115	-150	-86
Balance at End of Year	$425	$321	$424

Summary_of_Significant_Account5

Summary of Significant Accounting Policies - Estimated Useful Lives of Property and Equipment and Field Equipment (Detail)	12 Months Ended
	Dec. 31, 2014
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Leasehold improvements	Lesser of the lease term (including any renewal periods if appropriate) or estimated useful life of the asset
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Life	30 years
Manufacturing Equipment and Tooling [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Life	3 years
Manufacturing Equipment and Tooling [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Life	12 years
Computer and Office Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Life	3 years
Computer and Office Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Life	5 years
Molds [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Life	5 years
Molds [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Life	7 years
Furniture [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Life	5 years
Furniture [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Life	7 years
Field Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Life	5 years
Field Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Life	7 years

Summary_of_Significant_Account6

Summary of Significant Accounting Policies - Schedule of Rollforward of Warranty Accrual (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Abstract]
Balance at Beginning of Year	$297	$324	$380
Provision	441	412	540
Usage	-451	-439	-596
Balance at End of Year	$287	$297	$324

Inventory_Components_of_Invent

Inventory - Components of Inventory (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Inventory Disclosure [Abstract]
Purchased components	$19,238	$15,946
Work in process	9,981	10,762
Finished goods	16,182	11,093
Total	$45,401	$37,801

Property_and_Equipment_Field_E2

Property and Equipment, Field Equipment and Deferred Cost of Revenues - Summary of Components of Property and Equipment, Net (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$94,454	$74,270
Less accumulated depreciation	-27,880	-21,792
Property and equipment, net	66,574	52,478
Manufacturing Equipment and Tooling [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	34,621	24,963
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	18,485	11,883
Computer and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	8,935	4,132
Molds [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	5,377	3,817
Furniture [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,410	1,712
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	8,907	10,005
Land [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,110	1,258
Construction-in-Process [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$14,609	$16,500

Property_and_Equipment_Field_E3

Property and Equipment, Field Equipment and Deferred Cost of Revenues - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Depreciation expense for property and equipment	$7,100,000	$4,700,000	$3,700,000
Capitalized computer development costs	3,600,000
Amortization of capitalized computer development costs	900,000
Asset placed in service	66,574,000	52,478,000
Fair value in relation with incremental borrowing rate	50.00%
Amortization expense of deferred cost of revenue	13,500,000	13,300,000	13,500,000
Germany [Member]
Property, Plant and Equipment [Line Items]
Percentage of payments capped as cost of facility	50.00%
Percentage of purchase price to net book value of facility	100.00%
Capital lease obligation	12,700,000
Deferred revenues	8,200,000
Manufacturing Facility [Member]
Property, Plant and Equipment [Line Items]
Asset placed in service	6,400,000
Manufacturing Facility [Member] | Germany [Member]
Property, Plant and Equipment [Line Items]
Capital lease obligation	3,500,000
Deferred revenues	2,900,000
Computer and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Construction-in-process of capitalized computer development costs	0	4,500,000
Field Equipment [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense for field equipment	$4,200,000	$4,000,000	$3,700,000

Property_and_Equipment_Field_E4

Property and Equipment, Field Equipment and Deferred Cost of Revenues - Components of Assets Subject to Capital Leases (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]
Less accumulated depreciation	($2,905)
Assets subject to capital leases, net	22,283
Manufacturing Facility [Member] | Germany [Member]
Property, Plant and Equipment [Line Items]
Manufacturing facility in Germany/Other assets subject to capital leases	22,750
Assets Held under Capital Leases [Member]
Property, Plant and Equipment [Line Items]
Manufacturing facility in Germany/Other assets subject to capital leases	$2,438

Property_and_Equipment_Field_E5

Property and Equipment, Field Equipment and Deferred Cost of Revenues - Components of Field Equipment, Net (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]
Field equipment, net	$21,118	$13,041
Field Equipment [Member]
Property, Plant and Equipment [Line Items]
Field equipment	61,132	49,695
Less accumulated depreciation	-40,014	-36,654
Field equipment, net	$21,118	$13,041

Intangible_Assets_Summary_of_I

Intangible Assets - Summary of Intangible Assets (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Cost	$34,675	$34,685
Finite-Lived Intangible Assets, Accumulated Amortization	-20,305	-17,491
Bloodline Needle and Other Patented and Unpatented Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Cost	6,200	6,200
Finite-Lived Intangible Assets, Accumulated Amortization	-5,619	-4,844
Finite-Lived Intangible Assets, Estimated Useful Life	8 years
Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Cost	2,300	2,300
Finite-Lived Intangible Assets, Accumulated Amortization	-1,191	-1,026
Finite-Lived Intangible Assets, Estimated Useful Life	14 years
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Cost	26,175	26,185
Finite-Lived Intangible Assets, Accumulated Amortization	($13,495)	($11,621)
Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Estimated Useful Life	8 years
Minimum [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Estimated Useful Life	10 years
Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Estimated Useful Life	14 years
Maximum [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Estimated Useful Life	14 years

Intangible_Assets_Additional_I

Intangible Assets - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$2.80	$2.80	$2.80

Intangible_Assets_Estimated_Ag

Intangible Assets - Estimated Aggregated Amortization Expense for Intangible Assets (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Goodwill and Intangible Assets Disclosure [Abstract]
2015	$2,621
2016	2,040
2017	2,040
2018	2,040
2019	2,040
Thereafter	3,589
Total	$14,370	$17,194

Net_Loss_per_Share_Schedule_of

Net Loss per Share - Schedule of Anti-dilutive Net Loss Per Share (Detail)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common stock equivalents excluded from computation of earnings per share	1,112	1,165	2,719
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common stock equivalents excluded from computation of earnings per share	876	1,013	1,602
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common stock equivalents excluded from computation of earnings per share	236	152	196
Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common stock equivalents excluded from computation of earnings per share			921

Accrued_Expenses_Other_Current2

Accrued Expenses, Other Current Liabilities, and Other Long Term Liabilities - Components of Accrued Expenses (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Payables and Accruals [Abstract]
Payroll, compensation and related benefits	$12,346	$9,041
Distribution expenses	3,069	2,762
General and administrative expenses	3,075	2,207
Audit, legal, and consulting fees	1,394	2,725
Other	4,769	4,290
Total	$24,653	$21,025

Accrued_Expenses_Other_Current3

Accrued Expenses, Other Current Liabilities, and Other Long Term Liabilities - Components of Other Current Liabilities (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Other Liabilities Disclosure [Abstract]
Deferred revenue, current portion	$2,195
Capital lease obligations	2,246	1,471
Other	1,724	399
Total	$6,165	$1,870

Accrued_Expenses_Other_Current4

Accrued Expenses, Other Current Liabilities, and Other Long Term Liabilities - Components of Other Long-term Liabilities (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Other Liabilities, Noncurrent [Abstract]
Capital lease obligations	$11,876	$14,133
Lease incentive obligations	4,569	3,589
Benefit plan obligations	1,745	1,770
Other	1,434	781
Total	$19,624	$20,273

Debt_and_Capital_Lease_Obligat2

Debt and Capital Lease Obligations - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Jun. 10, 2014	31-May-13
Debt Instrument [Line Items]
Current portion of long-term debt	$93,000	$102,000
Revolving line of credit	35,000,000
Outstanding borrowings under revolving line of credit	0
Credit commitment available for borrowing	28,000,000
Silicon Valley Bank [Member]
Debt Instrument [Line Items]
Revolving line of credit	15,000,000
Revolving line of credit expiration date	31-Mar-14
General Electric Capital Corporation [Member]
Debt Instrument [Line Items]
Revolving line of credit expiration date	30-Jun-19
Maximum amount borrowed under new revolving line of credit			35,000,000
Line of credit facility interest rate description	(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
Mortgage One [Member]
Debt Instrument [Line Items]
Current portion of long-term debt				600,000
Interest rate on mortgage loan	6.00%
Mortgage Loan Period	10 years
Frequency of periodic payments	Payable quarterly over a 10 year period
Mortgage Two [Member]
Debt Instrument [Line Items]
Current portion of long-term debt				$500,000
Interest rate on mortgage loan	2.00%
Mortgage Loan Period	10 years
Frequency of periodic payments	Payable biannually over a 10 year period

Debt_and_Capital_Lease_Obligat3

Debt and Capital Lease Obligations - Schedule of Future Minimum Payments Under Capital Leases (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Debt Disclosure [Abstract]
2015	$2,326
2016	2,312
2017	1,925
2018	1,506
2019	851
Thereafter	9,065
Total minimum lease payments	17,985
Less amount representing interest	-3,863
Present value of future minimum lease payments	$14,122

Debt_and_Capital_Lease_Obligat4

Debt and Capital Lease Obligations - Schedule of Future Minimum Payments Under Capital Leases (Parenthetical) (Detail) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified
Debt Disclosure [Abstract]
Estimated residual value of manufacturing facility	$6.60

Business_Segment_and_Geographi2

Business Segment and Geographic Information - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2014
	Markets
	Segment
Segment Reporting [Abstract]
Number of reporting segments	3
Number of markets product distributed	3

Business_Segment_and_Geographi3

Business Segment and Geographic Information - Summary of Operating Performance of Reportable Segments (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenues									$301,501	$263,429	$242,132
Revenues	79,911	75,286	74,083	72,221	69,450	66,873	65,462	61,644	301,501	263,429	242,132
Segment profit (loss)	-4,473	-6,274	-6,651	-4,789	-4,578	-4,413	-4,271	-4,536	-22,187	-17,798	-11,206
Depreciation and amortization									27,697	24,848	23,673
Segment assets	309,726				306,962				309,726	306,962	311,949
Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment assets	173,685				140,811				173,685	140,811
Operating Segments [Member] | System One [Member]
Segment Reporting Information [Line Items]
Revenues									212,585	176,756	163,129
Revenues									846
Revenues									213,431	176,756	163,129
Segment profit (loss)									36,802	24,036	24,349
Depreciation and amortization									20,205	18,041	18,245
Segment assets	127,212				110,124				127,212	110,124	80,041
Operating Segments [Member] | In-Center [Member]
Segment Reporting Information [Line Items]
Revenues									78,885	81,852	76,927
Revenues									78,885	81,852	76,927
Segment profit (loss)									12,815	16,447	11,051
Depreciation and amortization									1,608	1,389	1,461
Segment assets	29,613				26,414				29,613	26,414	20,582
Operating Segments [Member] | Services [Member]
Segment Reporting Information [Line Items]
Revenues									1,749	352
Revenues									1,749	352
Segment profit (loss)									-14,926	-5,690	-1,218
Depreciation and amortization									1,055	135
Segment assets	16,860				4,273				16,860	4,273
Other Member]
Segment Reporting Information [Line Items]
Revenues									8,282	4,469	2,076
Revenues									8,282	4,469	2,076
Segment profit (loss)									-56,878	-52,591	-45,388
Depreciation and amortization									4,829	5,283	3,967
Segment assets	136,041				166,151				136,041	166,151	211,326
Intersegment Revenue Elimination [Member]
Segment Reporting Information [Line Items]
Revenues									-846
Revenues									($846)

Business_Segment_and_Geographi4

Business Segment and Geographic Information - Reconciliation of Total Segment Assets to Total Assets (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$309,726	$306,962	$311,949
Cash and cash equivalents	52,884	84,134	106,439	102,909
Property and equipment, net	66,574	52,478
Intangible assets, net	14,370	17,194
Goodwill	41,817	41,817
Operating Segments [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	173,685	140,811
Other Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	136,041	166,151	211,326
Cash and cash equivalents	52,884	84,134
Accounts Receivable, net	277	397
Property and equipment, net	17,269	17,000
Intangible assets, net	14,370	17,194
Goodwill	41,817	41,817
Prepaid and other assets	$9,424	$5,609

Business_Segment_and_Geographi5

Business Segment and Geographic Information - Total Long-Lived Tangible Assets by Geographic Area (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-Lived Assets	$87,692	$65,519	$46,421
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-Lived Assets	45,501	26,082	20,967
Mexico [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-Lived Assets	12,689	10,578	3,949
Other Americas [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-Lived Assets	482	94
Total Americas [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-Lived Assets	58,672	36,754	24,916
Germany [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-Lived Assets	21,246	20,235	17,058
Other Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-Lived Assets	7,774	8,530	4,447
Total Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-Lived Assets	$29,020	$28,765	$21,505

Business_Segment_and_Geographi6

Business Segment and Geographic Information - Summary of Number of Customers Who Individually Make Up Greater than 10% of Total Revenues (Detail) (Sales Revenue, Net [Member], Customer Concentration Risk [Member])	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
DaVita [Member]
Revenue, Major Customer [Line Items]
Percentage of revenues	21.00%	21.00%	21.00%
Fresenius [Member]
Revenue, Major Customer [Line Items]
Percentage of revenues	16.00%	14.00%	11.00%
Gambro [Member]
Revenue, Major Customer [Line Items]
Percentage of revenues	9.00%	12.00%	12.00%
Schein [Member]
Revenue, Major Customer [Line Items]
Percentage of revenues	8.00%	10.00%	11.00%

Commitments_and_Contingencies_1

Commitments and Contingencies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Commitments and Contingencies [Line Items]
Minimum purchase commitments	$62,300,000
Initial Lease period	11 years
Period for early termination provision of lease	After seven years
Rental description	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
Leasehold improvements allowance	4,300,000		4,300,000
Lease expiry period	2023
Rent expense	3,800,000	2,200,000	2,200,000
NxStage Kidney Care Facility [Member]
Commitments and Contingencies [Line Items]
Lease expiration year start	2018
Lease expiration year end	2022
Foreign Leased Manufacturing Facilities [Member]
Commitments and Contingencies [Line Items]
Lease expiration year start	2015
Lease expiration year end	2018
Minimum [Member]
Commitments and Contingencies [Line Items]
Purchase commitment period	1 year
Minimum [Member] | NxStage Kidney Care Facility [Member]
Commitments and Contingencies [Line Items]
Leasehold improvements allowance	100,000
Period of renewal of options	5 years
Maximum [Member]
Commitments and Contingencies [Line Items]
Purchase commitment period	5 years
Maximum [Member] | NxStage Kidney Care Facility [Member]
Commitments and Contingencies [Line Items]
Leasehold improvements allowance	$300,000
Period of renewal of options	10 years

Commitments_and_Contingencies_2

Commitments and Contingencies - Future Minimum Rental Payments Under Operating Leases (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Commitments and Contingencies Disclosure [Abstract]
2015	$4,412
2016	4,390
2017	4,244
2018	4,369
2019	3,535
Thereafter	8,523
Total	$29,473

Income_Taxes_Summary_of_Income

Income Taxes - Summary of Income (Loss) Before Income Taxes by Geography (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
U.S.	($24,315)	($20,613)	($16,026)
Foreign	1,255	1,807	1,906
Net loss before income taxes	($23,060)	($18,806)	($14,120)

Income_Taxes_Components_of_Pro

Income Taxes - Components of Provision for (Benefit from) Income Taxes (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current:
U.S. - State	$57	$47	$52
Foreign	1,278	-76	1,357
Total Current	1,335	-29	1,409
Deferred:
Foreign	-82	-216	-376
Total Deferred	-82	-216	-376
Total Provision (Benefit)	$1,253	($245)	$1,033

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Income Tax [Line Items]
Provision for (benefit from) income taxes	$1,253,000	($245,000)	$1,033,000
Foreign tax expense (benefit)	-1,200,000	-1,200,000
Excess tax deductions related to stock-based compensation	54,200,000
Excess tax deductions related to stock-based compensation, state	27,700,000
Foreign tax credit carryforward expiration dates	Between 2018 and 2021 if not utilized
Increase in deferred tax valuation allowance	9,100,000
Gross unrecognized tax benefits	400,000	500,000	1,500,000
Interest and penalties		100,000	400,000
Federal [Member]
Schedule of Income Tax [Line Items]
Net operating loss carryforward	366,000,000
Expiry period of net operating loss carryforward	Between 2015 and 2034 if not utilized
Federal [Member] | Research [Member]
Schedule of Income Tax [Line Items]
Research and development credit carryforward	7,000,000
Expiration year of research and development tax credit carryforward	2020
State [Member]
Schedule of Income Tax [Line Items]
Net operating loss carryforward	187,000,000
Expiry period of net operating loss carryforward	Between 2015 and 2034 if not utilized
State [Member] | Research [Member]
Schedule of Income Tax [Line Items]
Research and development credit carryforward	1,900,000
Foreign [Member] | Research [Member]
Schedule of Income Tax [Line Items]
Research and development credit carryforward	$1,000,000

Income_Taxes_Reconciliation_of

Income Taxes - Reconciliation of U.S. Federal Statutory Tax Rate to Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Federal statutory rate	34.00%	34.00%	34.00%
Stock compensation	2.00%	-2.50%	-5.60%
State income tax, net of federal tax benefit	1.90%	3.20%	2.00%
U.S. research credits	4.10%	11.70%	3.30%
Foreign income inclusion in the U.S.	-2.80%	-6.70%	-3.10%
Valuation allowance	-39.70%	-40.20%	-31.40%
Change in tax reserves		4.00%	-5.60%
Other, net	-4.90%	-2.20%	-0.90%
Effective tax rate	-5.40%	1.30%	-7.30%

Income_Taxes_Deferred_Tax_Asse

Income Taxes - Deferred Tax Assets (Liabilities) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Deferred tax assets:
Net operating loss carryforwards	$114,131	$108,772
Tax credits	10,078	9,464
Stock-based compensation	6,259	5,713
Capitalized research and development	3,120	3,677
Financing liabilities	6,281	5,007
Other	6,092	2,199
Total deferred tax assets	145,961	134,832
Deferred tax liabilities:
Fixed assets	-7,719	-5,079
Intangible assets	-5,326	-6,509
Other	-608
Total deferred tax liabilities	-13,653	-11,588
Net deferred tax assets before valuation allowance	132,308	123,244
Less valuation allowance	-131,453	-122,353
Net deferred tax assets	$855	$891

Income_Taxes_Changes_in_Unreco

Income Taxes - Changes in Unrecognized Tax Benefits (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Balance at beginning of the year	$411	$1,067	$678
Increase in unrecognized tax benefits current year	88	411	389
Decrease in unrecognized tax benefits prior years	-110
Reductions due to audit settlement	-42	-1,067
Balance at end of year	$347	$411	$1,067

Stock_Plans_and_StockBased_Com2

Stock Plans and Stock-Based Compensation - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
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	$4,900,000	$5,100,000	$5,100,000
Aggregate intrinsic value of options exercised	9,200,000	3,500,000	8,800,000
Share-based compensation expense	12,881,000	8,638,000	11,403,000
Weighted average period	2 years 7 months 6 days
Unrecognized stock compensation cost	19,000,000
Postemployment Benefits Liability, Noncurrent	1,745,000	1,770,000
2014 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Stock option expiration period	10 years
Reduction in number of shares available for grant	1.62
Share available for grant	5,300,000
Number of shares authorized for grant	5,600,000
Expiration date description	Ten years from the date of grant
Employee Stock Purchase Plan 2005 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share available for grant	100,000
Number of shares authorized for grant	700,000
Offering period	6 months
Eligibility for the participation in the 2005 purchase plan	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.
Price at which employee can purchase common stock in an offering	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
Price at which employee can purchase common stock in an offering percentage	95.00%
Weighted-average fair value of restricted stock granted	$1.46	$3.10	$4.57
Shares issued under employee stock purchase plan, Shares	70,899	75,301	56,691
Share-based compensation expense	100,000	100,000	200,000
Options to Purchase Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average fair value of options granted	$5.80	$6.29	$9.23
Options to Purchase Common Stock [Member] | 2014 Omnibus Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total fair value of restricted stock	$3,200,000	$2,800,000	$3,700,000
Weighted-average fair value of restricted stock granted	$14.35	$11.97	$16.89
Restricted Stock Units (RSUs) [Member] | 2014 Omnibus Incentive Plan [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Restricted Stock Units (RSUs) [Member] | 2014 Omnibus Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years

Stock_Plans_and_StockBased_Com3

Stock Plans and Stock-Based Compensation - Summary of Status of Stock Options Granted Under All Plans (Detail) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Beginning balance	4,825,880
Shares, granted	997,459
Shares, exercised	-1,524,601
Shares, forfeited or expired	-196,313
Ending balance	4,102,425
Shares, Fully vested and exercisable	2,822,955
Shares, fully vested, exercisable and expected to vest	3,956,565
Weighted average exercise price, outstanding at beginning of year	$10.73
Weighted average exercise price, granted	$14.35
Weighted average exercise price, exercised	$9.04
Weighted average exercise price, forfeited or expired	$15.17
Weighted average exercise price, outstanding at end of year	$12.02
Weighted average exercise price, fully vested and exercisable	$11.30
Weighted average exercise price, fully vested, exercisable and expected to vest	$11.96
Aggregate intrinsic value, outstanding at end of year	$24,832
Aggregate intrinsic value, fully vested and exercisable	19,264
Aggregate intrinsic value, fully vested, exercisable and expected to vest	$24,197
Average remaining contractual life, outstanding at end of year	5 years 2 months 5 days
Average remaining contractual life, fully vested and exercisable	3 years 8 months 23 days
Average remaining contractual life, fully vested, exercisable and expected to vest	5 years 22 days

Stock_Plans_and_StockBased_Com4

Stock Plans and Stock-Based Compensation - Estimated Fair Value of Options at Date of Grant (Detail) (Options to Purchase Common Stock [Member])	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life (in years)			4 years 6 months
Risk-free interest rate, Lower range	1.56%	0.75%	0.67%
Risk-free interest rate, Upper range	1.69%	1.04%	0.90%
Expected stock price volatility, Lower range	43.00%
Expected stock price volatility, Upper range	45.00%
Expected stock price volatility		62.00%	70.00%
Expected dividend yield	0.00%	0.00%	0.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life (in years)	4 years 4 months 24 days	4 years 6 months
Expected dividend yield	0.00%	0.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life (in years)	5 years	4 years 8 months 12 days
Expected dividend yield	0.00%	0.00%

Stock_Plans_and_StockBased_Com5

Stock Plans and Stock-Based Compensation - Summary of Status of Unvested Restricted Stock Units (Detail) (Restricted Stock [Member], USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested at December 31, 2013	734,221
Shares, granted	699,913
Shares, vested	-192,741
Shares, Forfeited	-51,548
Unvested at December 31, 2014	1,189,845	734,221
Weighted average grant date fair value unvested, Beginning balance	$14.72
Weighted average grant date fair value, granted	$14.35	$11.97	$16.89
Weighted average grant date fair value, vested	$16.64
Weighted average grant-date fair value, forfeited	$13.94
Weighted average grant date fair value unvested, Ending balance	$14.23	$14.72
Aggregate intrinsic value unvested, Beginning balance
Aggregate intrinsic value unvested, Ending balance	$21,334
Weighted average remaining contractual life unvested, Ending balance	1 year 10 months 21 days

Stock_Plans_and_StockBased_Com6

Stock Plans and Stock-Based Compensation - Valuation Assumptions for ESPP (Detail) (Employee Stock Purchase Plan 2005 [Member])	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee Stock Purchase Plan 2005 [Member]
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	0.07%	0.09%	0.06%
Risk-free interest rate, Upper range	0.10%	0.12%	0.15%
Expected stock price volatility, Lower range	26.30%	20.10%	23.30%
Expected stock price volatility, Upper range	27.40%	33.60%	36.00%
Expected dividend yield	0.00%	0.00%	0.00%

Stock_Plans_and_StockBased_Com7

Stock Plans and Stock-Based Compensation - Summary of Stock-Based Compensation Expense in Consolidated Statements of Comprehensive Loss (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$12,881	$8,638	$11,403
Cost of Revenues [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	1,212	918	1,168
Selling and Marketing [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	4,442	3,171	4,186
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	1,726	1,331	1,372
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$5,501	$3,218	$4,677

Employee_Benefit_Plan_Addition

Employee Benefit Plan - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Compensation and Retirement Disclosure [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	100% of the first 3% of the employee's contribution and 50% of the next 2% of the employee's contribution
Company's contribution cost recognized	$1.70	$1.50	$1.30

Stockholders_Equity_Additional

Stockholders' Equity - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity [Abstract]
Repayment of principal amount and interest			$45.20
Issuance of common stock for debt repayment			2,456,246
Number of shares retained for payment of minimum withholding taxes			28,351
Issuance of common stock for debt repayment, net			2,427,895
Warrants issued to purchase common stock		1,900,000
Exercise price of warrants, per share		$5.50
Shares delivered or surrendered in payment for the exercise of stock options	196,378	34,311	32,310

Business_Combination_Additiona

Business Combination - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Business acquisition, cash paid		$2,234,000
Discount rate used in determining fair value of customer relationships	11.50%
Customer Relationships [Member]
Business Acquisition [Line Items]
Discount rate used in determining fair value of customer relationships	11.50%
Kimal PLC [Member]
Business Acquisition [Line Items]
Business acquisition, aggregate purchase price		4,000,000
Business acquisition, cash paid	100,000	2,200,000
Business acquisition, liabilities assumed		1,500,000
Business acquisition, contingent consideration		500,000
Business acquisition,reclassification of deferred revenues		$300,000

Business_Combination_Allocatio

Business Combination - Allocation of Purchase Price to Estimated Fair Value of Assets Acquired (Detail) (Kimal PLC [Member], USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Kimal PLC [Member]
Assets purchased:
Inventory	$523
Field Equipment	3,298
Customer relationships	170
Assets acquired	$3,991

Derivative_Instruments_and_Hed2

Derivative Instruments and Hedging - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Hedging Transactions And Derivative Financial Instruments [Line Items]
Period of cash flow hedges	12 months
Cash Flow Hedges [Member]
Hedging Transactions And Derivative Financial Instruments [Line Items]
Notional amount of outstanding contracts	12.5	$10.40
Fair value of outstanding contracts liability	1.3	$0.20

Derivative_Instruments_and_Hed3

Derivative Instruments and Hedging - Effect of Contracts Designated as Cash Flow Hedges on Consolidated Financial Statements (Detail) (Cost of Revenues [Member], Cash Flow Hedges [Member], USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cost of Revenues [Member] | Cash Flow Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in OCI (Effective Portion)	($1,223)	$144	$498
Gain (Loss) Reclassified from OCI into Income (Effective Portion)	($258)	$656	$109
Classification within the Condensed Consolidated Statement of Comprehensive Loss	Cost of revenues

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive (Loss) Income - Summary of Additional Information on Accumulated Other Comprehensive (Loss) Income (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance net of tax	$212	$470	($68)
Other comprehensive loss before reclassifications	-2,662	398	647
(Gain) Loss reclassified to earnings	258	-656	-109
Total other comprehensive loss	-2,404	-258	538
Ending balance net of tax	-2,192	212	470
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance net of tax	335	81	-68
Other comprehensive loss before reclassifications	-1,439	254	149
Total other comprehensive loss	-1,439	254	149
Ending balance net of tax	-1,104	335	81
Unrealized Gain (Loss) on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance net of tax	-123	389
Other comprehensive loss before reclassifications	-1,223	144	498
(Gain) Loss reclassified to earnings	258	-656	-109
Total other comprehensive loss	-965	-512	389
Ending balance net of tax	($1,088)	($123)	$389

Fair_Value_Measurements_Schedu

Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (Fair Value Measurements, Recurring Basis [Member], USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Liabilities
Contingent consideration liability		$540
Foreign Exchange Forward Contracts [Member]
Assets
Foreign exchange forward contracts		34
Liabilities
Foreign exchange forward contracts	1,265	192
Significant Other Observable Inputs (Level 2) [Member] | Foreign Exchange Forward Contracts [Member]
Assets
Foreign exchange forward contracts		34
Liabilities
Foreign exchange forward contracts	1,265	192
Significant Unobservable Inputs (Level 3) [Member]
Liabilities
Contingent consideration liability		540
Money Market Funds [Member]
Assets
Money market funds	39,779	69,779
Money Market Funds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Money market funds	$39,779	$69,779

Fair_Value_Measurements_Roll_F

Fair Value Measurements - Roll Forward of Contingent Consideration Liability Classified as Level 3 within Value Hierarchy (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
Debt Instrument Fair Value Carrying Value [Abstract]
Balance at December 31, 2013	$540
Less: Payments made	-540
Balance at December 31, 2014	$0

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Discount rate	11.50%

Supplemental_Cash_Flow_Informa2

Supplemental Cash Flow Information - Summary of Supplemental Cash Flow Information (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplemental Disclosures:
Cash paid for interest	$671	$549	$1,457
Cash paid for taxes	903	1,181	586
Noncash Investing and Financing Activities:
Transfers from inventory to field equipment	25,370	13,827	12,172
Transfers from field equipment to deferred cost of revenues	13,110	10,260	10,360
Payment of Corporate Bonus Plan in common stock		1,034	878
Market value of shares received in payment for exercise of stock options	3,026	412	513
Construction-in-process financed by construction liability	4,898	3,568	8,343
Settlement of debt through the issuance of common stock			45,219
Leasehold improvements paid by the landlord	4,300		4,300
Property and equipment acquired under capital lease	76	745	1,615
Acquisition of business		1,757
Increase in deferred revenues related to the new manufacturing facility in Germany	3,608		6,124
Deferred revenues and deferred costs related to acquiree recorded as a reduction of consideration paid		$335

Quarterly_Financial_Data_Unaud2

Quarterly Financial Data (Unaudited) - Quarterly Financial Data (Unaudited) (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Revenues	$79,911	$75,286	$74,083	$72,221	$69,450	$66,873	$65,462	$61,644	$301,501	$263,429	$242,132
Gross profit	30,852	28,587	27,530	28,934	27,888	25,528	25,087	24,000	115,903	102,503	92,808
Loss from operations	-4,473	-6,274	-6,651	-4,789	-4,578	-4,413	-4,271	-4,536	-22,187	-17,798	-11,206
Net loss attributable to stockholders of NxStage Medical, Inc.	($4,852)	($6,706)	($7,113)	($5,275)	($5,176)	($4,986)	($3,405)	($4,994)	($23,946)	($18,561)	($15,153)
Net loss per share, basic and diluted	($0.08)	($0.11)	($0.12)	($0.09)	($0.08)	($0.08)	($0.06)	($0.08)	($0.39)	($0.31)	($0.26)