Chiasma (CHMA) 10-K 20 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Mar. 08, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	CHMA
Entity Registrant Name	CHIASMA, INC
Entity Central Index Key	1,339,469
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		24,381,605
Entity Public Float			$ 26,748,236

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current Assets
Cash and cash equivalents	$ 14,603	$ 37,013
Marketable securities	52,336	55,971
Prepaid expenses and other current assets	1,768	2,110
Total current assets	68,707	95,094
Property and equipment, net	193	683
Other assets	983	979
Total assets	69,883	96,756
Current liabilities
Accounts payable	1,017	1,166
Accrued expenses	4,033	5,534
Other current liabilities	1,695	1,700
Total current liabilities	6,745	8,400
Long-term liabilities	664	2,631
Total liabilities	7,409	11,031
Commitments and Contingencies (Note 14)
Stockholders' equity:
Common stock, $0.01 par value; authorized 125,000,000 shares at December 31, 2017 and December 31, 2016; issued and outstanding 24,381,605 shares at December 31, 2017 and 24,359,584 shares at December 31, 2016	244	244
Preferred stock, $0.01 par value; authorized 5,000,000 shares; none outstanding
Additional paid-in capital	267,642	264,017
Accumulated other comprehensive loss	(59)	(9)
Accumulated deficit	(205,353)	(178,527)
Total stockholders' equity	62,474	85,725
Total liabilities and stockholders' equity	$ 69,883	$ 96,756

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares issued	24,381,605	24,359,584
Common stock, shares outstanding	24,381,605	24,359,584
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares outstanding	0	0

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating expenses:
General and administrative	$ 9,146	$ 21,815	$ 16,456
Research and development	17,948	31,317	18,991
Restructuring charges	1,038	8,179
Total operating expenses	28,132	61,311	35,447
Loss from operations	(28,132)	(61,311)	(35,447)
Other expenses (income), net	(716)	(547)	300
Loss before income taxes	(27,416)	(60,764)	(35,747)
Provision (benefit) for income taxes	(590)	347	161
Net loss	(26,826)	(61,111)	(35,908)
Accretion of redeemable convertible preferred stock			(318)
Net loss attributable to common stockholders	$ (26,826)	$ (61,111)	$ (36,226)
Earnings per share attributable to common stockholders
Basic	$ (1.10)	$ (2.51)	$ (3.25)
Diluted	$ (1.10)	$ (2.51)	$ (3.25)
Weighted-average shares outstanding:
Basic	24,366,681	24,319,443	11,151,978
Diluted	24,366,681	24,319,443	11,151,978

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net loss	$ (26,826)	$ (61,111)	$ (35,908)
Other comprehensive income (loss):
Unrealized gains (losses) on available for sale securities, net	(50)	(32)	23
Total other comprehensive income (loss)	(50)	(32)	23
Comprehensive loss	$ (26,876)	$ (61,143)	$ (35,885)

Consolidated Statements of Rede

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($)	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income [Member]	Accumulated Deficit [Member]	Series B1' Redeemable Convertible Preferred Stock [Member]	Series C' Redeemable Convertible Preferred Stock [Member]	Series D' Redeemable Convertible Preferred Stock [Member]	Series E Redeemable Convertible Preferred Stock [Member]	Redeemable Convertible Preferred Stock [Member]
Beginning balance at Dec. 31, 2014						$ 9,144,000	$ 40,430,000	$ 22,054,000	$ 32,858,000	$ 104,486,000
Beginning balance at Dec. 31, 2014	$ (72,018,000)		$ 9,490,000		$ (81,508,000)
Beginning balance, shares at Dec. 31, 2014						1,134,997	40,430,250	38,504,439	33,774,763
Beginning balance, shares at Dec. 31, 2014		44,326
Stock-based compensation	3,258,000		3,258,000
Exercise of stock options	684,000	$ 2,000	682,000
Exercise of stock options, Shares		205,721
Exercise of warrants	14,000	$ 1,000	13,000
Exercise of warrants, Shares		39,789
Additional paid in capital on account of vested portion of restricted stock	63,000		63,000
Issuance of Redeemable convertible preferred stock and warrants for common stock, net of issuance costs	1,477,000		1,477,000						$ 34,213,000	34,213,000
Issuance of Redeemable convertible preferred stock and warrants for common stock, net of issuance costs, Shares									35,948,023
Issuance of common stock, conversion of preferred stock	139,017,000	$ 164,000	138,853,000			$ (9,144,000)	$ (40,430,000)	$ (22,054,000)	$ (67,389,000)	(139,017,000)
Issuance of common stock, conversion of preferred stock, Shares		16,403,011				(1,134,997)	(40,430,250)	(38,504,439)	(69,722,786)
Issuance of common stock, Initial public offering net of issuance costs of $ 2,394	106,524,000	$ 73,000	106,451,000
Issuance of common stock, Initial public offering net of issuance costs of $ 2,394 Shares		7,319,750
Accretion of redeemable convertible preferred stock									$ 318,000	$ 318,000
Accretion of redeemable convertible preferred stock	(318,000)		(318,000)
Other comprehensive income (loss)	23,000			$ 23,000
Net loss	(35,908,000)				(35,908,000)
Ending balance at Dec. 31, 2015	142,816,000	$ 240,000	259,969,000	23,000	(117,416,000)
Ending balance, shares at Dec. 31, 2015		24,012,597
Stock-based compensation	3,346,000		3,346,000
Exercise of stock options	600,000	$ 3,000	597,000
Exercise of stock options, Shares		292,235
Exercise of warrants	5,000	$ 1,000	4,000
Exercise of warrants, Shares		54,752
Additional paid in capital on account of vested portion of restricted stock	101,000		101,000
Other comprehensive income (loss)	(32,000)			(32,000)
Net loss	(61,111,000)				(61,111,000)
Ending balance at Dec. 31, 2016	85,725,000	$ 244,000	264,017,000	(9,000)	(178,527,000)
Ending balance, shares at Dec. 31, 2016		24,359,584
Stock-based compensation	3,522,000		3,522,000
Exercise of stock options	$ 2,000		2,000
Exercise of stock options, Shares	22,021	22,021
Additional paid in capital on account of vested portion of restricted stock	$ 101,000		101,000
Other comprehensive income (loss)	(50,000)			(50,000)
Net loss	(26,826,000)				(26,826,000)
Ending balance at Dec. 31, 2017	$ 62,474,000	$ 244,000	$ 267,642,000	$ (59,000)	$ (205,353,000)
Ending balance, shares at Dec. 31, 2017		24,381,605

Consolidated Statements of Red7

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)
Stock issuance cost	$ 2,394
Series E Redeemable Convertible Preferred Stock [Member]
Redeemable convertible preferred stock, issuance costs	$ 258

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Activities:
Net loss	$ (26,826)	$ (61,111)	$ (35,908)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation	152	433	201
Stock-based compensation	3,522	3,346	3,258
Amortization of premium on marketable securities, net	(150)	(150)	46
Benefit for deferred income taxes	(884)	(16)	(30)
Non-cash interest expense	131	246	349
Non-cash restructuring charges		1,474
Loss (gain) on sale of property and equipment		67	(5)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	820	674	(1,737)
Accounts payable and accrued expenses	(1,616)	1,805	496
Other assets	402	(14)	(171)
Other current and long-term liabilities	25	1,282	198
Net cash used in operating activities	(24,424)	(51,964)	(33,303)
Investing Activities:
Purchase of marketable securities	(89,163)	(117,146)	(108,236)
Maturities of marketable securities	92,898	169,006	500
Decrease in value of other assets			(1,119)
Purchases of property and equipment	(23)	(2,964)	(269)
Proceeds from sale of property and equipment		137	12
Net cash provided by (used in) investing activities	3,712	49,033	(109,112)
Financing Activities:
Payment under license termination agreement	(1,700)	(1,700)
Proceeds from the issuance of common stock, net			106,524
Proceeds from issuance of restricted stock			382
Exercise of warrants		5	14
Exercise of stock options	2	600	684
Net cash provided by (used in) financing activities	(1,698)	(1,095)	143,294
Net increase (decrease) in cash and cash equivalents	(22,410)	(4,026)	879
Cash and cash equivalents, beginning of year	37,013	41,039	40,160
Cash and cash equivalents, end of year	14,603	37,013	41,039
Supplemental Non-Cash Financing Activities:
Conversion of preferred stock			139,017
Supplemental disclosures of cash flow information:
Cash paid for income taxes	$ 51	$ 140	69
Cash received for interest			33
Series E Redeemable Convertible Preferred Stock [Member]
Financing Activities:
Proceeds from issuance of Series E redeemable convertible preferred stock and warrants for common stock, net			$ 35,690

Nature of Business

Nature of Business	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business	1. Nature of Business Chiasma, Inc. is a clinical-stage biopharmaceutical company incorporated in 2001 under the laws of the State of Delaware. Chiasma, Inc. is headquartered in Massachusetts and has two wholly owned subsidiaries; Chiasma (Israel) Ltd., and Chiasma Securities Corp, collectively referred to as “the Company,” “we,” “us”, “our” or “Chiasma”. We are a clinical-stage biopharmaceutical company focused on improving the lives of patients who face challenges associated with their existing treatments for rare and serious chronic disease. Employing our proprietary Transient Permeability Enhancer (“TPE”) technology platform, we seek to develop oral medications that are currently available only as injections. We are currently developing oral octreotide capsules, conditionally trade-named “MYCAPSSA”, our sole TPE platform-based clinical product candidate, in two Phase 3 clinical trials in adult patients for the treatment of acromegaly to potentially support regulatory approval in the United States and Europe. Acromegaly is a rare and debilitating condition that results in the body’s production of excess growth hormone. Octreotide is an analog of somatostatin, a natural inhibitor of growth hormone secretion. Octreotide capsules have been granted orphan designation in the United States and the European Union for the treatment of acromegaly. We retain worldwide rights to develop and commercialize octreotide capsules with no royalty obligations to third parties. In September 2017, we initiated a third Phase 3 clinical trial for oral octreotide capsules for the maintenance therapy of adult patients with acromegaly following our agreement with the United States Food and Drug Administration (“FDA”) on the design of the trial, reached through a Special Protocol Assessment in August 2017. The trial, referred to as CHIASMA OPTIMAL, is a randomized, double-blind, placebo-controlled, nine-month trial expected to enroll 50 adult acromegaly patients designed to support regulatory approval of octreotide capsules in the United States. We are also currently conducting an international Phase 3 clinical trial, referred to as MPOWERED, of oral octreotide capsules for the maintenance treatment of adult patients with acromegaly to support regulatory approval in Europe. The MPOWERED trial is a global, randomized, open-label and active-controlled 15-month trial expected to enroll approximately 130 adult acromegaly patients, of which we expect to randomize at least 80 patients who are responders to octreotide capsules following a six-month run-in to either octreotide capsules or injectable somatostatin receptor ligands (octreotide or lanreotide), and then followed for an additional nine months.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
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 Chiasma, Inc. and its subsidiaries and are prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and are stated in U.S. dollars. The consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities in the ordinary course of business. All intercompany balances and transactions have been eliminated in consolidation. On July 21, 2015, we completed the sale of 7,319,750 shares of our common stock in our IPO, at a price to the public of $16.00 per share, resulting in net proceeds to us of approximately $106.5 million after deducting underwriting discounts and commissions and offering expenses payable by us. In connection with the closing of the IPO on July 21, 2015, all of our outstanding redeemable convertible preferred stock automatically converted into 16,403,011 shares of common stock. The significant increase in shares outstanding in July 2015 impacted the year-over-year comparability of our net loss per share calculations for the year ended December 31, 2015. Liquidity We have incurred significant losses from operations since our inception and expect losses to continue for at least the next several years. We are heavily dependent on the regulatory approval and subsequent commercial success of our product candidate, octreotide capsules for the treatment of acromegaly in the United States and Europe, both of which may never occur. We expect to continue with our ongoing international Phase 3 CHIASMA OPTIMAL clinical trial of octreotide capsules in acromegaly to support potential regulatory approval in the United States and ongoing international Phase 3 MPOWERED clinical trial of octreotide capsules in acromegaly to support potential regulatory approval in Europe. In June and August 2016, we announced two separate corporate restructuring plans, which were completed in 2017, intended to focus our resources on the continued development of octreotide capsules for the maintenance treatment of adult acromegaly patients. We currently expect our existing cash, cash equivalents and marketable securities to fund our operations for at least one year after the date these consolidated financial statements are issued. We expect to continue to incur significant operating losses for the foreseeable future. Successful transition to attaining profitable operations is dependent upon achieving a level of revenues adequate to support our cost structure. We plan to continue to fund our losses from operations and capital funding needs from existing balances of cash, cash equivalents and marketable securities and potentially through the issuance of debt and/or equity or through collaborations or license agreements with other companies. Debt or equity financing may not be available on a timely basis on terms acceptable to us, or at all. If we are not able to secure adequate additional funding, we may be forced to make further reductions in spending, extend payment terms with suppliers, liquidate assets where possible, or suspend or curtail our planned development of octreotide capsules. Any of these actions could materially harm our business, results of operations and future prospects. Failure to obtain regulatory approval of octreotide capsules in acromegaly will prevent us from commercializing the product candidate, which could raise significant concerns about our continued viability as a business. Use of estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. We base these estimates and assumptions on historical experience when available, and on various factors that we believe to be reasonable under the specific circumstances. Significant estimates relied upon in preparing the accompanying consolidated financial statements include, but are not limited to, the fair value of common stock and other equity instruments, accounting for stock-based compensation, present value of long-term purchase obligation, income taxes, and accounting for certain accruals. We assess these estimates on an ongoing basis; however, actual results could materially differ from those estimates. Cash Equivalents Cash and cash equivalents consist of highly liquid instruments which mature within three months or less from the date of purchase. Marketable Securities Our investments primarily consist of commercial paper and corporate and government debt securities. These marketable securities are classified as available-for-sale, and as such, are reported at fair value on our consolidated balance sheets. Unrealized holding gains and losses are reported within accumulated other comprehensive income as a separate component of stockholders’ equity. The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization, together with interest on securities, are included in other expenses (income), net, on our consolidated statements of operations. If a decline in the fair value of a marketable security below our cost basis is determined to be other than temporary, such marketable security is written down to its estimated fair value as a new cost basis and the amount of the write-down is included in earnings as an impairment charge. The cost of securities sold is based on the specific identification method. Foreign currency translation We use the U.S. dollar as our functional currency. Monetary assets and liabilities denominated in foreign currency are re-measured at current rates and non-monetary assets denominated in foreign currency are recorded at historical exchange rates. Realized and unrealized exchange gains or losses from transactions and re-measurement adjustments are reflected in other expense (income), net, in the accompanying consolidated statements of operations. Comprehensive income (loss) Comprehensive income (loss) is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. Other than reported net income, comprehensive income (loss) includes unrealized gains and losses on available for sale securities, which are disclosed in the accompanying consolidated statements of comprehensive income. There were no reclassifications out of comprehensive income (loss) for the years ended December 31, 2017, 2016 or 2015. Segment information Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, our Chief Executive Officer, in making decisions regarding resource allocation and assessing performance. We view our operations and manage our business in one operating segment. Other assets Other assets consist of long-term restricted deposits, prepayments, and deferred tax assets. Long-term restricted deposits represent interest-bearing money market accounts held as security deposits against bank guarantees. Concentrations of credit risk Financial instruments that potentially subject us to significant concentration of credit risk consist primarily of cash, cash equivalents, and marketable securities. We routinely maintain deposits in financial institutions in excess of government insured limits. Management believes that we are not exposed to significant credit risk as our deposits are held at financial institutions that management believes to be of high credit quality and we have not experienced any significant losses in these deposits. We regularly invest excess operating cash in deposits with major financial institutions and money market funds and in notes issued by the U.S. government, as well as in fixed income investments and bond funds, both of which can be readily purchased and sold using established markets. We believe that the market risk arising from our holdings of these financial instruments is mitigated based on the fact that many of these securities are either government backed or of high credit rating. Property and equipment Property and equipment are stated at cost, net of accumulated depreciation and amortization. Expenditures for maintenance and repairs are charged to operations as incurred, whereas major betterments are capitalized as additions to property and equipment. Depreciation and amortization are recorded using the straight-line method over the estimated useful lives of the assets, as follows: Asset Category Estimated Useful Lives Computer equipment and software 3 years Office furniture and equipment 7—17 years (mainly 7) Laboratory equipment 7—17 years (mainly 10) Leasehold improvements The lesser of lease term Impairment of long-lived assets We review long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. When such events occur, we compare the carrying amounts of the assets to their undiscounted expected future cash flows the assets are expected to generate and to be recognized. The amount of impairment loss to be recognized is the excess of the carrying value over the fair value of the related asset. We did not record any impairments during the years ended December 31, 2017, 2016 (other than described in Note 17) and 2015. Employment termination costs We accrue employment termination liabilities when (a) management, having the authority to approve the action, commits to a plan of termination; (b) the plan identifies the number of employees to be terminated, their job classifications or functions, their locations, and the expected completion date; (c) the plan establishes the terms of the arrangement, including the benefits that employees will receive upon termination, in sufficient detail to enable employees to determine the type and amount of benefits they will receive upon involuntary termination; (d) it is unlikely that significant changes to the plan will be made or withdrawn; and (e) the plan has been communicated to the affected employees. When employees are required to render services beyond the minimum retention period through the involuntary termination date in order to receive the termination benefits, a liability is measured initially at the communication date based on the fair value of the liability, and is recognized ratably over the future service period through expected termination date. We reverse the liability when events or circumstances occur that discharge or remove its responsibility to settle the termination liability. Long-term purchase obligation Our long-term purchase obligation represents aggregate amounts payable to F. Hoffman- La Roche Ltd. and Hoffmann-La Roche Inc. (collectively “Roche”) for the purchase of certain active pharmaceutical ingredient (“API”) supplies and the trade name (“MYCAPSSA”) for octreotide capsules following the termination of our license agreement with Roche in July 2014. The amount is payable in three equal annual installments and is recorded at its present value. The difference between the aggregate purchase price and the present value of the installment payments represents the interest component of the financing arrangement and is recorded as interest expense over the payment term and included in other expenses (income), net, in the accompanying consolidated statements of operations. Research and development Research and development costs are expensed as incurred. Research and development costs include payroll and personnel expense, consulting costs, external contract research and development expenses, raw materials, drug product manufacturing costs, and allocated overhead including depreciation and amortization, rent, and utilities. Research and development costs that are paid in advance of performance are capitalized as a prepaid expense and amortized over the service period as the services are provided. Clinical trial costs Clinical trial costs are a component of research and development expenses. We accrue and expense clinical trial activities performed by third parties on an evaluation of the progress to completion of specific tasks using data such as hours spent in performance of services, patient enrollment, clinical site activation, and other information provided to us by our vendors. We make estimates of our clinical trial accrued expenses as of each balance sheet date in our financial statements based on facts and circumstances known to us. If timelines or contracts are modified based upon changes in the clinical trial protocol or scope of work to be performed, we assess our estimates of accrued expenses accordingly. Patent costs Patent costs are expensed as incurred as their realization is uncertain. These costs are classified as general and administrative in the accompanying consolidated statements of operations. Redeemable convertible preferred stock We classify redeemable convertible preferred stock as temporary equity in the accompanying consolidated statement of redeemable convertible preferred stock and stockholders’ equity (deficit) due to redemption rights granted to the holders that are outside of our control. We recorded redeemable convertible stock initially at the original issuance price net of issuance costs and discounts, if any, according to relative fair value method. When the initial recorded amount is less than the redemption value, we accrete the recorded amount up to the redemption value over the redemption period using the effective interest method, plus dividends expected to be paid upon redemption, if any. We accrete the recorded amount up to the deemed liquidation upon the occurrence of any such event. On the effective date of our IPO, the redeemable convertible preferred stock automatically converted into common stock. Warrants Common stock warrants issued in connection with the issuance of redeemable convertible preferred stock were classified as a component of stockholders’ equity because they are free standing financial instruments that are legally detachable and separately exercisable from the redeemable convertible preferred stock, are contingently exercisable, do not embody an obligation for us to repurchase the shares, and permit the holders to receive a fixed number of common shares upon exercise. In addition, the common stock warrants require physical settlement and do not provide any guarantee of value or return. Common stock warrants were initially recorded at their relative fair value and were not subsequently re-measured. Common stock warrants were valued using Black-Scholes option pricing model. Stock-based compensation We account for all stock-based compensation to employees and nonemployees based on their fair values on the date of grant. The fair value of stock-based awards to nonemployees is remeasured as the award vests. For employee stock-based awards with only service conditions, we recognize compensation on a straight-line basis over the requisite service period, which is usually the vesting period of the award, net of any actual forfeitures. We determine the fair value of stock options by using the Black-Scholes option pricing model. This model requires the input of several assumptions such as the expected option term, the expected risk-free interest rate over the expected option term, the expected volatility of our stock price over the expected option term, and the expected dividend yield over the expected option term. The computation of expected volatility is based on an average historical share price volatility based on an analysis of reported data for a peer group of comparable publicly traded companies, which were selected based upon industry similarities. The interest rate for periods within the expected term of the award is based on the U.S. Treasury risk-free interest rate in effect at the time of grant. The expected lives of the options were estimated using the simplified method. For options granted to non-employees, the expected life of the option used is the contractual term of each such option. All other assumptions used to calculate the grant date fair value are generally consistent with the assumptions used for options granted to employees. Stock-based compensation expense for awards granted to non-employees is adjusted as the award vests to reflect the current fair value of such awards, and is recognized using an accelerated attribution model. Income taxes The consolidated financial statements reflect provisions for federal, state, local and foreign income taxes. Deferred tax assets and liabilities represent future tax consequences of temporary differences between the financial statement carrying amounts and the tax basis of assets and liabilities and for loss carryforwards using enacted tax rates expected to be in effect in the years in which the differences reverse. A valuation allowance is recorded when it is more likely than not that some or all of the deferred tax assets will not be realized. We determine whether it is more likely than not that a tax position will be sustained upon examination. If it is not more likely than not that a position will be sustained, none of the benefit attributable to the position is recognized. The tax benefit to be recognized for any tax position that meets the more likely than not recognition threshold is calculated as the largest amount that is more than 50% likely of being realized upon resolution of the contingency. We account for interest and penalties related to uncertain tax positions as part of our other expenses in the accompanying consolidated financial statements. Contingent liabilities In the normal course of business, we are subject to proceedings, lawsuits, and other claims and assessments. We assess the likelihood of any adverse judgments or outcomes to these matters as well as potential ranges of probable losses. A determination of the amount of reserves required, if any, for these contingencies is made after careful analysis of each individual issue. The required reserves may change in the future due to new developments in each matter or changes in approach such as a change in settlement strategy in dealing with these matters. We record charges for the losses we anticipate incurring in connection with litigation and claims against us when we conclude a loss is probable and we can reasonably estimate these losses. Earnings per share attributable to common stockholders We compute basic earnings per share attributable to common stockholders by dividing net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period. During periods in which we incurred a net loss, we allocate no net loss to participating securities because they do not have a contractual obligation to share in the net loss. We compute diluted earnings per common share after giving consideration to all potentially dilutive common shares, including stock options, and warrants outstanding during the period except where the effect of such non-participating securities would be antidilutive. Recently issued accounting pronouncements In February 2016, the Financial Accounting Standards Board issued new guidance which establishes a right-of-use model that requires a lessee to record an asset and a lease liability on the balance sheet for all leases with terms longer than 12 months. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. The new standard is effective for annual periods beginning after December 15, 2018, including interim periods within those annual reporting periods. A modified retrospective transition approach, which includes a number of optional practical expedients that we may elect to apply, is required for lessees for capital and operating leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. We are currently evaluating the impact the standard may have on our consolidated financial statements and we currently expect that most of our operating lease commitments will be subject to the new standard and recognized as operating lease liabilities and right-of-use assets upon adoption.

Investments

Investments	12 Months Ended
	Dec. 31, 2017
Investments Schedule [Abstract]
Investments	3. Investments Our investments consisted of the following as of December 31, 2017 and 2016: As of December 31, 2017 Amortized Cost Gross Gains Gross Losses Estimated ($ in thousands) Money market funds $ 12,399 $ — $ — $ 12,399 Corporate notes 29,788 — (35 ) 29,753 Commercial paper 22,607 1 (25 ) 22,583 Total $ 64,794 $ 1 $ (60 ) $ 64,735 As of December 31, 2016 Amortized Cost Gross Gains Gross Losses Estimated ($ in thousands) Money market funds $ 35,218 $ — $ — $ 35,218 Corporate notes 22,347 — (7 ) 22,340 Commercial paper 33,633 7 (9 ) 33,631 Total $ 91,198 $ 7 $ (16 ) $ 91,189 As of December 31, 2017, we do not consider those securities that are in an unrealized loss position to be other-than-temporarily impaired, as we have the ability to hold such investments until recovery of the fair value. We utilize the specific identification method in computing realized gains and losses. We had no realized gains and losses on our available-for-sale securities for the years ended December 31, 2017, 2016 or 2015. The fair values of our investments by classification in our consolidated balance sheets as of December 31, 2017 and 2016 were as follows: As of December 31, 2017 2016 ($ in thousands) Cash and cash equivalents $ 12,399 $ 35,218 Marketable securities 52,336 55,971 Total $ 64,735 $ 91,189 Cash and cash equivalents in the table above exclude cash of $2.2 million and $1.8 million as of December 31, 2017 and 2016, respectively. The contractual maturity dates of all of our investments are less than one year.

Fair Value Measurements and Fai

Fair Value Measurements and Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements and Fair Value of Financial Instruments	4. Fair Value Measurements and Fair Value of Financial Instruments Certain assets and liabilities are reported at fair value on a recurring basis. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date. The fair value accounting guidance requires that assets and liabilities carried at fair value be classified and disclosed in one of the following three categories: Level 1— Quoted prices in active markets for identical assets or liabilities that we have the ability to access at the measurement date. Level 2— Inputs other than quoted prices in active markets that are observable for the asset or liability, either directly or indirectly. Level 3— Inputs that are unobservable for the asset or liability. To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by us in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The following tables summarize the fair value measurements of our financial instruments as of December 31, 2017 and 2016: Fair Value Measurements at December 31, 2017 Quoted Prices in Active Markets Significant Observable Significant Unobservable Inputs (Level 3) Total ($ in thousands) Cash equivalents: Money market funds $ 12,399 $ — $ — $ 12,399 Total cash equivalents $ 12,399 $ — $ — $ 12,399 Marketable securities: Corporate notes $ — $ 29,753 $ — $ 29,753 Commercial paper — 22,583 — 22,583 Total marketable securities — 52,336 — 52,336 Total $ 12,399 $ 52,336 $ — $ 64,735 Fair Value Measurements at December 31, 2016 Quoted Prices in Active Markets Significant Observable Significant Unobservable Inputs (Level 3) Total ($ in thousands) Cash equivalents: Money market funds $ 35,218 $ — $ — $ 35,218 Total cash equivalents $ 35,218 $ — $ — $ 35,218 Marketable securities: Corporate notes $ — $ 22,340 $ — $ 22,340 Commercial paper — 33,631 — 33,631 Total marketable securities — 55,971 — 55,971 Total $ 35,218 $ 55,971 $ — $ 91,189 Our cash equivalents are classified as Level 1 assets under the fair value hierarchy as these assets have been valued using quoted market prices in active markets and do not have any restrictions on redemption. Our marketable securities are classified as Level 2 assets under the fair value hierarchy as these assets were primarily determined from independent pricing services, which normally derive security prices from recently reported trades for identical or similar securities, making adjustments based upon other significant observable market transactions. At the end of each reporting period, we perform quantitative and qualitative analysis of prices received from third parties to determine whether prices are reasonable estimates of fair value. After completing our analysis, we did not adjust or override any fair value measurements provided by our pricing services as of December 31, 2017 or 2016. We did not have any Level 3 assets being measured at fair value on a recurring basis as of December 31, 2017 or 2016. There were no transfers between measurement levels during the years ended December 31, 2017 and 2016.

Earnings per Share Attributable

Earnings per Share Attributable to Common Stockholders	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings per Share Attributable to Common Stockholders	5. Earnings per Share Attributable to Common Stockholders All common stock warrants and stock options have been excluded from the computation of diluted weighted-average shares outstanding because such securities would have an anti-dilutive impact due to net losses reported during the years ended December 31, 2017, 2016 and 2015. Since we have reported a net loss attributable to common stockholders for the years ended December 31, 2017, 2016 and 2015, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders for those periods.

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property and Equipment	6. Property and Equipment Property and equipment consisted of the following as of December 31, 2017 and 2016: As of December 31, 2017 2016 ($ in thousands) Computer equipment and software $ 359 $ 406 Office furniture and equipment 173 593 Property and equipment, at cost 532 999 Less accumulated depreciation (339 ) (316 ) Property and equipment, net $ 193 $ 683 Depreciation expense was $0.2 million, $0.4 million and $0.2 million for the years ended December 31, 2017, 2016 and 2015, respectively.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued Expenses	7. Accrued Expenses Accrued expenses consisted of the following as of December 31, 2017 and 2016: As of December 31, 2017 2016 ($ in thousands) Accrued general and administrative expenses $ 752 $ 547 Accrued research and development expenses 2,501 2,107 Accrued payroll and employee benefits 780 2,597 Accrued restructuring costs — 283 Total accrued expenses $ 4,033 $ 5,534

License Agreement

License Agreement	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
License Agreement	8. License Agreement In December 2012, we signed a license agreement with Roche, which was effective in January 2013, and granted Roche an exclusive, non-transferable license to our intellectual property related to the octreotide capsules. Under the terms of the agreement, Roche obtained worldwide rights to research, develop, make, import, export, sell, market or distribute the commercial product. We retained certain research and development activities under a joint development plan and all rights to the intellectual property contained in the agreement. In July 2014, Roche terminated the license agreement. Upon termination, Roche returned all rights and documentation granted under the agreement to us. We were relieved of further obligations under the agreement. Following the termination of the license agreement, we are not entitled to further payments from Roche, Roche has no remaining rights to octreotide capsules and we retain all rights to octreotide capsules and all related intellectual property. Subsequent to the termination, we purchased from Roche API supplies to continue the development and manufacturing of octreotide capsules as well as Roche’s proposed trade name for octreotide capsules for an aggregate amount of $5.1 million payable in three equal annual installments of $1.7 million beginning in 2016. We made the $1.7 million annual payments in March of 2018, 2017, and 2016. The difference between the aggregate purchase price and the present value of the installment payments represents the interest component of the financing arrangement and is being recorded as interest expense over the payment term. Other than these payments, we have no other financial and operational obligations to Roche.

Warrants

Warrants	12 Months Ended
	Dec. 31, 2017
Text Block [Abstract]
Warrants	9. Warrants As of December 31, 2015, there were warrants outstanding for the purchase of 3,621,767 shares of common stock with exercise prices ranging from $0.09 to $9.13. The warrants were issued at various points between June 2011 and February 2015 with expiration dates ranging from June 2016 through February 2025. There were no warrants exercised during the year ended December 31, 2017. There were 54,752 warrants exercised during the year ended December 31, 2016. There were warrants for the purchase of 3,567,015 shares of common stock outstanding as of December 31, 2017.

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Redeemable Convertible Preferred Stock	10. Redeemable Convertible Preferred Stock During the years ended December 2012 and 2013, we issued an aggregate of 38,504,439 shares of Series D redeemable convertible preferred stock (the “Series D preferred”) and warrants to purchase up to an aggregate of 1,698,066 shares of Common Stock at an exercise price of $0.09 per share (the “Warrants”), for aggregate gross proceeds of $38.5 million, of which $34.8 million was allocated to the Series D preferred and $3.6 million was allocated to the Warrants, net of issuance cost in the amount of $0.1 million. Since the Series D preferred was issued in conjunction with freestanding detachable warrants, the proceeds from the issuance were allocated to each freestanding instrument based on their relative fair value. We accreted the discount amount due to the Warrants allocation and issuance cost, using the interest method, until August 2014 which was the earliest redemption date of the instrument according to our certificate of incorporation then in effect. In March 2013, we redeemed our Series B1 redeemable convertible preferred stock (“Series B1 preferred”), Series C preferred, and Series D preferred (“collectively, the “Original Preferred Stock”) using proceeds received from the license agreement with Roche (see Note 8), which redemption was effected in accordance with the deemed liquidation provisions of our certificate of incorporation then in effect. Pursuant to such deemed liquidation provisions, upon such an event the Series D preferred was entitled to a redemption amount equal to its original issuance price plus $38.5 million. Accordingly, we immediately recognized the change in the redemption value in the amount of $38.5 million against accumulated deficit. The consideration for the redemption consisted of a cash payment of $55.0 million and the issuance of 1,134,997 shares of Series B1’ redeemable convertible preferred stock (“Series B1’ preferred”), 40,430,250 shares of Series C’ redeemable convertible preferred stock (“Series C’ preferred”), and 38,504,439 shares of Series D’ redeemable convertible preferred stock (“Series D’ preferred”, and collectively with the Series B1’ preferred and Series C’ preferred, the “Prime Preferred Stock”). The Prime Preferred Stock bears similar terms, rights and preferences as the Original Preferred Stock, other than changes to reflect redemption payment of Series D preferred described above. In addition, the holders of the Original Preferred Stock received rights to receive future contingent payments under the Roche license agreement. Upon termination of the license agreement, these rights were also terminated. The initial carrying value of the Prime Preferred Stock equaled the carrying value of the Original Preferred Stock on the redemption date. We accreted the carrying value of the Series D’ preferred to its redemption value until August 2014, which was the earliest redemption date of the Series D’ preferred according to our certificate of incorporation. In December 2014, we issued 33,774,763 shares of Series E redeemable convertible preferred stock (“Series E preferred”) at $1.00 per share, resulting in gross proceeds of $33.8 million, with issuance costs of $0.2 million. In connection with the issuance of Series E preferred, we issued to the holders warrants to purchase 924,622 shares of our common stock with an exercise price of $9.13 per share and allocated $0.8 million of the net proceeds to the warrants based on their relative fair value on the issuance date which was accounted for as a discount on Series E preferred and recorded as additional paid-in capital. In February 2015, we increased the number of authorized shares of Series E redeemable convertible preferred stock (“Series E preferred”) to a total of 80,774,458 shares and subsequently sold and issued an aggregate of 35,948,023 shares of Series E preferred at $1.00 per share for gross proceeds of $35.9 million, with of issuance costs of $0.3 million. In connection with the issuance of Series E preferred, we issued to the holders of Series E preferred warrants to purchase 984,116 shares of our common stock, with an exercise price of $9.13 per share and allocated $1.5 million of the net proceeds to the warrants based on their relative fair value on the issuance date which was accounted for as a discount on Series E preferred and recorded as additional paid in capital. In connection with the closing of the IPO on July 21, 2015, all of the outstanding redeemable convertible preferred stock automatically converted into 16,403,011 shares of common stock.

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Common Stock	11. Common Stock On July 21, 2015, we issued 7,319,750 shares of our common stock, $0.01 par value per share, at a price to the public of $16.00 per share before underwriting discounts. We raised approximately $106.5 million in net proceeds after deducting underwriting discounts and commissions and offering expenses.

Stock Incentive Plan

Stock Incentive Plan	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Incentive Plan	12. Stock Incentive Plan In 2008, our Board of Directors adopted the 2008 Stock Incentive Plan (the “2008 Plan”), which provided for the grant of incentive stock options, nonqualified stock options, and restricted stock to our employees, directors, and nonemployees up to 3,547,741 shares of common stock. Option awards expire 10 years from the grant date and generally vest over four years, but vesting conditions can vary at the discretion of our Board of Directors. In July 2015, we approved a 2015 Stock Option and Incentive Plan (the “2015 Plan”), which became effective upon our IPO. The 2015 Plan allows the grant of incentive stock options, nonqualified stock options, and restricted stock to employees, directors, and nonemployees of Chiasma up to 3,566,296 shares of common stock. In connection with the adoption of the 2015 Plan, no further option grants are permitted under the 2008 Plan and any expirations, cancellations, or terminations under the previous plan are available for issuance under the 2015 Plan. On January 1, 2016, the number of shares reserved and available for issuance under the 2015 Stock Plan increased by 960,504 shares of common stock pursuant to a provision in the 2015 Stock Plan that provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2016, by 4% of the number of shares of common stock issued and outstanding on the immediately preceding December 31 or such lesser number as determined by the compensation committee of the Board of Directors. The compensation committee of the Board of Directors determined there would be no increase to the shares reserved and available under the 2015 Stock Plan on January 1, 2018 and 2017. As of December 31, 2017, the total number of shares authorized for stock award plans is 7,114,037 of which 3,190,015 remain available for grant. There are 3,609,766 stock options outstanding as of December 31, 2017. The fair value of each stock option issued was estimated at the date of grant using the following weighted-average assumptions: For the Years 2017 2016 2015 Expected volatility 74 % 75 % 75 % Expected term (years) 5.69 6.22 6.26 Risk-free interest rate 1.81 % 1.45 % 1.71 % Expected dividend yield 0 % 0 % 0 % A summary of option activity as of December 31, 2017 and the year then ended is presented below: Number of Stock Options Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (Years) Aggregate Intrinsic Value Outstanding, January 1, 2017 3,652,801 $ 4.95 8.27 $ 779,340 Exercised (22,021 ) $ 0.09 Granted 116,750 $ 1.48 Forfeited/Expired (137,764 ) $ 9.18 Outstanding, December 31, 2017 3,609,766 $ 4.71 7.38 $ 668,434 Exercisable, December 31, 2017 2,250,316 $ 4.68 6.80 $ 632,034 Vested and expected to vest, December 31, 2017 3,609,766 $ 4.71 $ 7.38 $ 668,434 The weighted-average grant date per-share fair value of stock options granted during 2017, 2016 and 2015 was $0.95, $4.38 and $6.76, respectively. The aggregate intrinsic value of stock options exercised during the years ended December 31, 2017, 2016 and 2015 was approximately $40,000, $3.5 million and $1.8 million, respectively. At December 31, 2017, there was $4.1 million of unrecognized compensation cost related to stock options, which is expected to be recognized over a weighted-average period of 2.0 years. Stock-based compensation expense for 2017, 2016 and 2015 consisted of the following: For the Years 2017 2016 2015 ($ in thousands) General and administrative $ 1,510 $ 1,717 $ 1,848 Research and development 2,012 1,629 1,410 Total $ 3,522 $ 3,346 $ 3,258 During 2015, two directors exercised options to purchase an aggregate of 122,644 shares of common stock of which 116,258 of the shares were issued as restricted stock as they were exercised prior to full vesting. The proceeds from the issuance of the restricted stock are presented as long-term liabilities within the accompanying consolidated balance sheet, since we have the right to repurchase the unvested portion of the restricted stock following termination of the services of their holder. The long-term liability is released to additional paid-in capital per the original vesting schedule of the options. As of December 31, 2017, there were 35,772 restricted shares outstanding and the outstanding balance of the liability was $0.1 million. The weighted average grant date fair value of the options was $2.62.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	13. Income Taxes Our loss before provision for income taxes for the years ended December 31, 2017, 2016 and 2015 consisted of the following: For the Years Ended December 31, 2017 2016 2015 ($ in thousands) Domestic $ (27,703 ) $ (61,390 ) $ (35,219 ) Foreign 287 626 (528 ) Total $ (27,416 ) $ (60,764 ) $ (35,747 ) The components of income tax provision (benefit) consisted of the following for the years ended December 31, 2017, 2016 and 2015: For the Years Ended December 31, 2017 2016 2015 ($ in thousands) Current provision for income taxes: U.S. $ 13 $ 12 $ — Foreign 281 351 191 Total current provision for income taxes 294 363 191 Deferred tax benefit - U.S. Federal (956 ) — — Deferred tax provision (benefit) - foreign 72 (16 ) (30 ) Total deferred benefit for income taxes (884 ) (16 ) (30 ) Total provision (benefit) for income taxes $ (590 ) $ 347 $ 161 A reconciliation setting forth the differences between our effective tax rates and the U.S. federal statutory tax rate is as follows: For the Years 2017 2016 2015 U.S. federal tax provision at statutory rate 34.00 % 34.00 % 34.00 % State and local tax, net of federal benefit 4.39 % 4.75 % 5.64 % Foreign rate differences 0.79 % 0.42 % 0.08 % Non-deductible foreign stock compensation (1.73 %) (0.63 %) (1.16 %) Effect of other permanent differences (0.66 %) (0.29 %) (0.05 %) Uncertain tax positions 0.13 % (0.03 %) (0.53 %) Change in valuation allowance 33.17 % (39.99 %) (37.74 %) Federal Tax Reform Rate Change (68.55 %) 0.00 % 0.00 % Other adjustments 0.62 % 1.16 % (0.69 %) Effective tax rate 2.16 % (0.61 %) (0.45 %) Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income and for tax carryforwards. Significant components of our deferred tax assets and liabilities as of December 31, 2017 and 2016 are as follows: As of December 31, 2017 2016 ($ in thousands) Deferred tax assets: Federal and state net operating loss carryforwards $ 37,882 $ 44,778 Tax credit carryforwards — 1,024 Intangible and other related assets 312 347 Accrued expenses 627 1,826 Stock compensation 1,067 979 Other 120 251 Total deferred tax assets 40,008 49,205 Valuation allowance (39,984 ) (49,119 ) Net deferred tax assets $ 24 $ 86 When realization of a deferred tax asset is more likely than not to occur, the benefit related to the deductible temporary differences attributable to operations is recognized as a reduction of income tax expense. Valuation allowances are provided against deferred tax assets when, based on all available evidence, it is considered more likely than not that some portion or all of the recorded deferred tax assets will not be realized in future periods. We cannot be certain that future U.S. taxable income will be sufficient to realize our deferred tax assets. Accordingly, a full valuation allowance has been provided against our U.S. net deferred tax assets. The valuation allowance decreased by $9.1 million and increased by $24.3 million in 2017 and 2016, respectively. The decrease in 2017 is primarily related to Federal tax reform reducing the Federal tax rate to 21% which resulted in a decrease to our deferred assets and a corresponding decrease to the valuation allowance. The increase in 2016 is primarily the result of an increase in net operating loss (“NOL”) carryforwards. In December 2017, the Tax Cuts and Jobs Act of 2017 (“tax reform” or the “tax law”) was enacted. The tax reform reduced our U.S. corporate income tax rate from 34% to 21% beginning in 2018. Deferred tax assets and liabilities are measured using the enacted rate for the period in which they are expected to reverse. Accordingly, the reduction to the U.S. Federal corporate tax rate reduced our net U.S. deferred tax asset by $18.8 million which was offset by a corresponding reduction to its valuation allowance. In addition, the tax reform includes a transition tax in which all foreign earnings are deemed to be repatriated to the U.S. We are in the process of calculating the impact of the transition tax. Pursuant to Staff Accounting Bulletin No. 118, our measurement period for the tax impact of the transition tax is still open. At this time, we do not anticipate future material adjustments to our financial statements due to the transition tax. At December 31, 2017, we had U.S. Federal and state NOL carryforwards totaling approximately $146.4 million and $113.1 million, respectively, that expire at various dates through 2037. At December 31, 2017, we had no Israeli NOL carryforwards, and approximately $1.0 million of U.S. Federal alternative minimum tax credit carryforwards that do not expire. The tax reform also allows us to receive the U.S. Federal alternative minimum tax credit carryforward in the form of a refund from 2018 through 2021. We have a history of generating losses and are forecasting that we will not generate taxable income through 2021 which would otherwise limit our ability to realize the U.S. Federal alternative minimum tax credit. Accordingly, we have recorded a receivable of $1.0 million for the U.S. Federal alternative minimum tax credit refund in the accompanying consolidated balance sheet as of December 31, 2017. Under Section 382 of the Internal Revenue Code of 1986, as amended, substantial changes in our ownership may limit the amount of NOL carryforwards that can be utilized annually in the future to offset our U.S. Federal taxable income. Specifically, this limitation may arise in the event of a cumulative change in our ownership of more than 50% within any three-year period. We have determined that we experienced an ownership change for purposes of Section 382 in August 2005 and May 2008. These ownership changes resulted in annual limitations to the amount of NOL carryforwards that can be utilized to offset future taxable income, if any, at the U.S. Federal level. The annual limit is approximately $0.1 million for 2008, and each year thereafter. We are currently in the process of performing a Section 382 study for our year ended December 31, 2017. At this point in time, it is uncertain if we have undergone an ownership change as defined by Section 382. If we have in fact undergone an ownership change, our NOL carryforwards may be substantially limited. Our Israeli subsidiary has been recognized as a research and development company by the Head of the Israeli Administration of Industrial Research and Development and is entitled to tax benefits by virtue of the “beneficiary enterprise” status granted to part of its business activities under the Israeli Law for the Encouragement of Capital Investments 1959. The tax benefits include reduced tax rates on the research and development portion of its income during the first ten years of the benefit period (commenced in 2008). We benefit from a 20.6% tax rate for its income derived from research and development activities. Our tax rate on income from non-research and development activities is 24.0%. The continued application of the tax benefits is subject to certain conditions as defined by Israeli law. As part of the transition tax provision, we have a deemed repatriation of all of our undistributed earnings as of December 31, 2017. However, our subsidiary’s earnings, if distributed, would still be subject to local withholding tax and state income taxes. The subsidiary has undistributed earnings of approximately $2.3 million as of December 31, 2017, which is considered to be permanently reinvested in the operations of the subsidiary. If the earnings were to be distributed to the U.S. parent, they would be subject to Israeli withholding and state income tax liabilities. The unrecognized deferred tax liability is approximately $0.3 million. We file U.S. federal, various state and Israeli income tax returns. The associated tax filings remain subject to examination by applicable tax authorities for a certain length of time following the tax year to which those filings relate. As we are in a loss carry-forward position, we are generally subject to U.S. Federal and state examinations for all years for which the Company generated losses that are included in the available losses carried forward to the current period. As of December 31, 2017, a summary of the tax years that remain subject to examination in our taxing jurisdictions is as follows: United States 2003 and forward Israel 2013 and forward We have reviewed the tax positions taken, or to be taken, in our tax returns for all tax years currently open to examination by a taxing authority. We have recorded minimal interest or penalties related to uncertain tax positions. We remain subject to examination until the statute of limitations expires for each respective tax jurisdiction. The statute of limitations will be open with respect to these tax positions until 2021. A reconciliation of the beginning and ending amount of our unrecognized tax benefits is as follows: For the Years 2017 2016 2015 ($ in thousands) Uncertain tax position at the beginning of year $ 460 $ 429 $ 241 Additions for uncertain tax positions of prior year 45 — — Additions for uncertain tax positions of current year — 40 188 Reductions for settlements with taxing authorities — — — Reductions for lapses of the applicable statutes of limitations (34 ) (9 ) — Uncertain tax position at the end of the year $ 471 $ 460 $ 429

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	14. Commitments and Contingencies We conduct certain of our operations in leased facilities, which are accounted for as operating leases. Certain leases include renewal options. In addition, we lease automobiles and equipment under operating leases. There were no assets held under capital leases at December 31, 2017 and 2016. Rent expense was as follows for 2017, 2016 and 2015: For the Years 2017 2016 2015 ($ in thousands) Rent Expense $ 945 $ 1,221 $ 347 At December 31, 2017, the minimum rental commitments under all non-cancelable operating leases with initial or remaining terms of more than one year, for each of the following fiscal years, are as follows: For the Years Ended December 31, 2018 2019 2020 2021 2022 Thereafter ($ in thousands) Operating Leases $ 156 $ 110 $ 104 $ — $ — $ — Legal Proceedings On June 9, 2016, Chiasma, Inc. and certain of our current and former officers were named as defendants in a purported federal securities class action lawsuit filed in the United States District Court for the District of Massachusetts, styled Gerneth v. Chiasma, Inc., et al

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	15. Related Party Transactions In August 2014, we signed a consulting agreement, which was amended in January 2016 and December 2016, with one of our investors and a representative of this investor to serve as our head of clinical. Costs incurred for services rendered by the head of clinical were $0.2 million, $0.5 million and $0.4 million for the years ended December 31, 2017, 2016 and 2015, respectively. Related to this consulting agreement, there were $0.1 million and $0.2 million of accrued liabilities as of December 31, 2017 and 2016, respectively, recorded in our consolidated balance sheets. In December 2014, we entered into a consulting agreement with a representative of another investor to provide financial and strategic consulting services to us. This agreement was terminated in March 2016. During the years ended December 31, 2016 and 2015, we recorded $0.2 million and $0.9 million, respectively, of expense related to this agreement, and which were classified as general and administrative expenses in the accompanying consolidated statements of operations.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2017
Postemployment Benefits [Abstract]
Employee Benefit Plans	16. Employee Benefit Plans Pursuant to the Israeli Severance Pay Law 1963, Israeli employees are entitled to severance pay equal to one month’s salary for each year of employment, or a portion thereof. The employees of Chiasma (Israel) Ltd. are included under Section 14 of the Severance Pay Law, under which these employees are entitled to monthly deposits, which relieve us from future obligations under this law. As a result, no assets or liabilities are recorded in the accompanying consolidated balance sheets. In addition, we make mandated monthly contributions to an Israeli government retirement benefit plan for our Israeli employees. Beginning in 2016, we provide a 401(k) profit-sharing plan covering eligible U.S. employees to make tax deferred contributions, a portion of which are matched by us. All matching contributions and participant contributions vest immediately. During the years ended December 31, 2017, 2016 and 2015, we recorded expenses of $0.2 million, $0.5 million and $0.1 million, respectively related to these employee benefit plans.

Restructuring Charges

Restructuring Charges	12 Months Ended
	Dec. 31, 2017
Restructuring and Related Activities [Abstract]
Restructuring Charges	17. Restructuring Charges In November 2017, we finalized the termination of our lease agreement on our 24,000 square foot office facility in Waltham, MA which we no longer required following the 2016 workforce reductions. As a result, we recorded approximately $1.0 million of restructuring expenses during the year ended December 31, 2017, which consisted of a lease termination payment of $1.0 million, the write-off of office furniture and equipment of $0.4 million offset by the release of deferred rent liabilities of $0.4 million associated with the terminated lease. In June 2016, we announced a corporate restructuring plan, including an immediate reduction of approximately 33% of our workforce, including substantially all of our commercial personnel. In August 2016, we announced a second corporate restructuring plan, including an immediate reduction of approximately 44% of our remaining workforce. In aggregate, these restructuring plans resulted in a reduction to our workforce of more than 60% since May 1, 2016. As a result of the August reduction in force, we no longer required the research lab and additional office space of the Israel facility and we were able to early terminate the Israel lease in November 2016. Accordingly, we recorded restructuring charges totaling $8.2 million during the year ended December 31, 2016 which consisted of employee severance benefits and related costs of $2.2 million, manufacturing commitment-related suspension fees of $4.5 million, non-cash restructuring charges of $0.8 million resulting from the impairment of leasehold improvements of $1.7 million offset by the forgiveness of tenant allowances received under the lease of $0.9 million and non-cash restructuring charges related to the impairment of previously capitalized commercial software and laboratory equipment of $0.7 million. The components of our restructuring charges are as follows: 2017 2016 ($ in thousands) Severance benefits and related costs $ — $ 2,211 Lease termination fees 1,038 — Non-cash restructuring charges — 1,474 Manufacturing suspension fees — 4,494 Total $ 1,038 $ 8,179 Activity related to accrued restructuring costs is as follows: 2017 2016 ($ in thousands) Balance at beginning of year $ 283 $ — Plus: Current year restructuring costs 1,038 8,179 Less: Lease termination costs 1,038 — Payment of employee severance costs 283 1,928 Payment of manufacturing suspension fees — 4,494 Non-cash restructuring charges — 1,474 Balance at end of year $ — $ 283

Other Expenses (Income), net

Other Expenses (Income), net	12 Months Ended
	Dec. 31, 2017
Other Income and Expenses [Abstract]
Other Expenses (Income), net	18. Other Expenses (Income), net Other expenses (income), net are as follows: For the Years 2017 2016 2015 ($ in thousands) Loss / (Gain) on foreign currency transactions, net $ 81 $ (9 ) $ — Interest income (928 ) (802 ) (128 ) Interest expense 131 264 349 Other expenses — — 79 Total $ (716 ) $ (547 ) $ 300

Quarterly Financial Data (unaud

Quarterly Financial Data (unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data (unaudited)	19. Quarterly Financial Data (unaudited) Three Months Ended March 31, 2017 June 30, 2017 September 30, 2017 December 31, 2017 ($ in thousands, except for per share data) Loss from operations $ (7,115 ) $ (6,920 ) $ (6,943 ) $ (7,154 ) Net loss (7,020 ) (6,854 ) (6,849 ) (6,103 ) Net loss attributable to common stockholders (7,020 ) (6,854 ) (6,849 ) (6,103 ) Earnings per share attributed to common stockholders - Basic $ (0.29 ) $ (0.28 ) $ (0.28 ) $ (0.25 ) Diluted $ (0.29 ) $ (0.28 ) $ (0.28 ) $ (0.25 ) Three Months Ended March 31, 2016 June 30, 2016 September 30, 2016 December 31, 2016 ($ in thousands, except for per share data) Loss from operations $ (17,220 ) $ (26,708 ) $ (9,439 ) $ (7,944 ) Net loss (17,180 ) (26,663 ) (9,373 ) (7,895 ) Net loss attributable to common stockholders (17,180 ) (26,663 ) (9,373 ) (7,895 ) Earnings per share attributed to common stockholders - Basic $ (0.71 ) $ (1.10 ) $ (0.38 ) $ (0.32 ) Diluted $ (0.71 ) $ (1.10 ) $ (0.38 ) $ (0.32 )

Summary of Significant Accoun28

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
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 Chiasma, Inc. and its subsidiaries and are prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and are stated in U.S. dollars. The consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities in the ordinary course of business. All intercompany balances and transactions have been eliminated in consolidation. On July 21, 2015, we completed the sale of 7,319,750 shares of our common stock in our IPO, at a price to the public of $16.00 per share, resulting in net proceeds to us of approximately $106.5 million after deducting underwriting discounts and commissions and offering expenses payable by us. In connection with the closing of the IPO on July 21, 2015, all of our outstanding redeemable convertible preferred stock automatically converted into 16,403,011 shares of common stock. The significant increase in shares outstanding in July 2015 impacted the year-over-year comparability of our net loss per share calculations for the year ended December 31, 2015.
Liquidity	Liquidity We have incurred significant losses from operations since our inception and expect losses to continue for at least the next several years. We are heavily dependent on the regulatory approval and subsequent commercial success of our product candidate, octreotide capsules for the treatment of acromegaly in the United States and Europe, both of which may never occur. We expect to continue with our ongoing international Phase 3 CHIASMA OPTIMAL clinical trial of octreotide capsules in acromegaly to support potential regulatory approval in the United States and ongoing international Phase 3 MPOWERED clinical trial of octreotide capsules in acromegaly to support potential regulatory approval in Europe. In June and August 2016, we announced two separate corporate restructuring plans, which were completed in 2017, intended to focus our resources on the continued development of octreotide capsules for the maintenance treatment of adult acromegaly patients. We currently expect our existing cash, cash equivalents and marketable securities to fund our operations for at least one year after the date these consolidated financial statements are issued. We expect to continue to incur significant operating losses for the foreseeable future. Successful transition to attaining profitable operations is dependent upon achieving a level of revenues adequate to support our cost structure. We plan to continue to fund our losses from operations and capital funding needs from existing balances of cash, cash equivalents and marketable securities and potentially through the issuance of debt and/or equity or through collaborations or license agreements with other companies. Debt or equity financing may not be available on a timely basis on terms acceptable to us, or at all. If we are not able to secure adequate additional funding, we may be forced to make further reductions in spending, extend payment terms with suppliers, liquidate assets where possible, or suspend or curtail our planned development of octreotide capsules. Any of these actions could materially harm our business, results of operations and future prospects. Failure to obtain regulatory approval of octreotide capsules in acromegaly will prevent us from commercializing the product candidate, which could raise significant concerns about our continued viability as a business.
Use of estimates	Use of estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. We base these estimates and assumptions on historical experience when available, and on various factors that we believe to be reasonable under the specific circumstances. Significant estimates relied upon in preparing the accompanying consolidated financial statements include, but are not limited to, the fair value of common stock and other equity instruments, accounting for stock-based compensation, present value of long-term purchase obligation, income taxes, and accounting for certain accruals. We assess these estimates on an ongoing basis; however, actual results could materially differ from those estimates.
Cash Equivalents	Cash Equivalents Cash and cash equivalents consist of highly liquid instruments which mature within three months or less from the date of purchase.
Marketable Securities	Marketable Securities Our investments primarily consist of commercial paper and corporate and government debt securities. These marketable securities are classified as available-for-sale, and as such, are reported at fair value on our consolidated balance sheets. Unrealized holding gains and losses are reported within accumulated other comprehensive income as a separate component of stockholders’ equity. The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization, together with interest on securities, are included in other expenses (income), net, on our consolidated statements of operations. If a decline in the fair value of a marketable security below our cost basis is determined to be other than temporary, such marketable security is written down to its estimated fair value as a new cost basis and the amount of the write-down is included in earnings as an impairment charge. The cost of securities sold is based on the specific identification method.
Foreign currency translation	Foreign currency translation We use the U.S. dollar as our functional currency. Monetary assets and liabilities denominated in foreign currency are re-measured at current rates and non-monetary assets denominated in foreign currency are recorded at historical exchange rates. Realized and unrealized exchange gains or losses from transactions and re-measurement adjustments are reflected in other expense (income), net, in the accompanying consolidated statements of operations.
Comprehensive income (loss)	Comprehensive income (loss) Comprehensive income (loss) is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. Other than reported net income, comprehensive income (loss) includes unrealized gains and losses on available for sale securities, which are disclosed in the accompanying consolidated statements of comprehensive income. There were no reclassifications out of comprehensive income (loss) for the years ended December 31, 2017, 2016 or 2015.
Segment information	Segment information Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, our Chief Executive Officer, in making decisions regarding resource allocation and assessing performance. We view our operations and manage our business in one operating segment.
Other assets	Other assets Other assets consist of long-term restricted deposits, prepayments, and deferred tax assets. Long-term restricted deposits represent interest-bearing money market accounts held as security deposits against bank guarantees.
Concentrations of credit risk	Concentrations of credit risk Financial instruments that potentially subject us to significant concentration of credit risk consist primarily of cash, cash equivalents, and marketable securities. We routinely maintain deposits in financial institutions in excess of government insured limits. Management believes that we are not exposed to significant credit risk as our deposits are held at financial institutions that management believes to be of high credit quality and we have not experienced any significant losses in these deposits. We regularly invest excess operating cash in deposits with major financial institutions and money market funds and in notes issued by the U.S. government, as well as in fixed income investments and bond funds, both of which can be readily purchased and sold using established markets. We believe that the market risk arising from our holdings of these financial instruments is mitigated based on the fact that many of these securities are either government backed or of high credit rating.
Property and equipment	Property and equipment Property and equipment are stated at cost, net of accumulated depreciation and amortization. Expenditures for maintenance and repairs are charged to operations as incurred, whereas major betterments are capitalized as additions to property and equipment. Depreciation and amortization are recorded using the straight-line method over the estimated useful lives of the assets, as follows: Asset Category Estimated Useful Lives Computer equipment and software 3 years Office furniture and equipment 7—17 years (mainly 7) Laboratory equipment 7—17 years (mainly 10) Leasehold improvements The lesser of lease term
Impairment of long-lived assets	Impairment of long-lived assets We review long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. When such events occur, we compare the carrying amounts of the assets to their undiscounted expected future cash flows the assets are expected to generate and to be recognized. The amount of impairment loss to be recognized is the excess of the carrying value over the fair value of the related asset. We did not record any impairments during the years ended December 31, 2017, 2016 (other than described in Note 17) and 2015.
Employment termination costs	Employment termination costs We accrue employment termination liabilities when (a) management, having the authority to approve the action, commits to a plan of termination; (b) the plan identifies the number of employees to be terminated, their job classifications or functions, their locations, and the expected completion date; (c) the plan establishes the terms of the arrangement, including the benefits that employees will receive upon termination, in sufficient detail to enable employees to determine the type and amount of benefits they will receive upon involuntary termination; (d) it is unlikely that significant changes to the plan will be made or withdrawn; and (e) the plan has been communicated to the affected employees. When employees are required to render services beyond the minimum retention period through the involuntary termination date in order to receive the termination benefits, a liability is measured initially at the communication date based on the fair value of the liability, and is recognized ratably over the future service period through expected termination date. We reverse the liability when events or circumstances occur that discharge or remove its responsibility to settle the termination liability.
Long-term purchase obligation	Long-term purchase obligation Our long-term purchase obligation represents aggregate amounts payable to F. Hoffman- La Roche Ltd. and Hoffmann-La Roche Inc. (collectively “Roche”) for the purchase of certain active pharmaceutical ingredient (“API”) supplies and the trade name (“MYCAPSSA”) for octreotide capsules following the termination of our license agreement with Roche in July 2014. The amount is payable in three equal annual installments and is recorded at its present value. The difference between the aggregate purchase price and the present value of the installment payments represents the interest component of the financing arrangement and is recorded as interest expense over the payment term and included in other expenses (income), net, in the accompanying consolidated statements of operations.
Research and development	Research and development Research and development costs are expensed as incurred. Research and development costs include payroll and personnel expense, consulting costs, external contract research and development expenses, raw materials, drug product manufacturing costs, and allocated overhead including depreciation and amortization, rent, and utilities. Research and development costs that are paid in advance of performance are capitalized as a prepaid expense and amortized over the service period as the services are provided.
Clinical trial costs	Clinical trial costs Clinical trial costs are a component of research and development expenses. We accrue and expense clinical trial activities performed by third parties on an evaluation of the progress to completion of specific tasks using data such as hours spent in performance of services, patient enrollment, clinical site activation, and other information provided to us by our vendors. We make estimates of our clinical trial accrued expenses as of each balance sheet date in our financial statements based on facts and circumstances known to us. If timelines or contracts are modified based upon changes in the clinical trial protocol or scope of work to be performed, we assess our estimates of accrued expenses accordingly.
Patent costs	Patent costs Patent costs are expensed as incurred as their realization is uncertain. These costs are classified as general and administrative in the accompanying consolidated statements of operations.
Redeemable convertible preferred stock	Redeemable convertible preferred stock We classify redeemable convertible preferred stock as temporary equity in the accompanying consolidated statement of redeemable convertible preferred stock and stockholders’ equity (deficit) due to redemption rights granted to the holders that are outside of our control. We recorded redeemable convertible stock initially at the original issuance price net of issuance costs and discounts, if any, according to relative fair value method. When the initial recorded amount is less than the redemption value, we accrete the recorded amount up to the redemption value over the redemption period using the effective interest method, plus dividends expected to be paid upon redemption, if any. We accrete the recorded amount up to the deemed liquidation upon the occurrence of any such event. On the effective date of our IPO, the redeemable convertible preferred stock automatically converted into common stock.
Warrants	Warrants Common stock warrants issued in connection with the issuance of redeemable convertible preferred stock were classified as a component of stockholders’ equity because they are free standing financial instruments that are legally detachable and separately exercisable from the redeemable convertible preferred stock, are contingently exercisable, do not embody an obligation for us to repurchase the shares, and permit the holders to receive a fixed number of common shares upon exercise. In addition, the common stock warrants require physical settlement and do not provide any guarantee of value or return. Common stock warrants were initially recorded at their relative fair value and were not subsequently re-measured. Common stock warrants were valued using Black-Scholes option pricing model
Stock-based compensation	Stock-based compensation We account for all stock-based compensation to employees and nonemployees based on their fair values on the date of grant. The fair value of stock-based awards to nonemployees is remeasured as the award vests. For employee stock-based awards with only service conditions, we recognize compensation on a straight-line basis over the requisite service period, which is usually the vesting period of the award, net of any actual forfeitures. We determine the fair value of stock options by using the Black-Scholes option pricing model. This model requires the input of several assumptions such as the expected option term, the expected risk-free interest rate over the expected option term, the expected volatility of our stock price over the expected option term, and the expected dividend yield over the expected option term. The computation of expected volatility is based on an average historical share price volatility based on an analysis of reported data for a peer group of comparable publicly traded companies, which were selected based upon industry similarities. The interest rate for periods within the expected term of the award is based on the U.S. Treasury risk-free interest rate in effect at the time of grant. The expected lives of the options were estimated using the simplified method. For options granted to non-employees, the expected life of the option used is the contractual term of each such option. All other assumptions used to calculate the grant date fair value are generally consistent with the assumptions used for options granted to employees. Stock-based compensation expense for awards granted to non-employees is adjusted as the award vests to reflect the current fair value of such awards, and is recognized using an accelerated attribution model.
Income taxes	Income taxes The consolidated financial statements reflect provisions for federal, state, local and foreign income taxes. Deferred tax assets and liabilities represent future tax consequences of temporary differences between the financial statement carrying amounts and the tax basis of assets and liabilities and for loss carryforwards using enacted tax rates expected to be in effect in the years in which the differences reverse. A valuation allowance is recorded when it is more likely than not that some or all of the deferred tax assets will not be realized. We determine whether it is more likely than not that a tax position will be sustained upon examination. If it is not more likely than not that a position will be sustained, none of the benefit attributable to the position is recognized. The tax benefit to be recognized for any tax position that meets the more likely than not recognition threshold is calculated as the largest amount that is more than 50% likely of being realized upon resolution of the contingency. We account for interest and penalties related to uncertain tax positions as part of our other expenses in the accompanying consolidated financial statements.
Contingent liabilities	Contingent liabilities In the normal course of business, we are subject to proceedings, lawsuits, and other claims and assessments. We assess the likelihood of any adverse judgments or outcomes to these matters as well as potential ranges of probable losses. A determination of the amount of reserves required, if any, for these contingencies is made after careful analysis of each individual issue. The required reserves may change in the future due to new developments in each matter or changes in approach such as a change in settlement strategy in dealing with these matters. We record charges for the losses we anticipate incurring in connection with litigation and claims against us when we conclude a loss is probable and we can reasonably estimate these losses. Earnings per share attributable to common stockholders We compute basic earnings per share attributable to common stockholders by dividing net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period. During periods in which we incurred a net loss, we allocate no net loss to participating securities because they do not have a contractual obligation to share in the net loss. We compute diluted earnings per common share after giving consideration to all potentially dilutive common shares, including stock options, and warrants outstanding during the period except where the effect of such non-participating securities would be antidilutive.
Recently issued accounting pronouncements	Recently issued accounting pronouncements In February 2016, the Financial Accounting Standards Board issued new guidance which establishes a right-of-use model that requires a lessee to record an asset and a lease liability on the balance sheet for all leases with terms longer than 12 months. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. The new standard is effective for annual periods beginning after December 15, 2018, including interim periods within those annual reporting periods. A modified retrospective transition approach, which includes a number of optional practical expedients that we may elect to apply, is required for lessees for capital and operating leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements. We are currently evaluating the impact the standard may have on our consolidated financial statements and we currently expect that most of our operating lease commitments will be subject to the new standard and recognized as operating lease liabilities and right-of-use assets upon adoption.

Summary of Significant Accoun29

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Schedule of Estimated Useful Lives of Assets	Depreciation and amortization are recorded using the straight-line method over the estimated useful lives of the assets, as follows: Asset Category Estimated Useful Lives Computer equipment and software 3 years Office furniture and equipment 7—17 years (mainly 7) Laboratory equipment 7—17 years (mainly 10) Leasehold improvements The lesser of lease term

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2017
Investments Schedule [Abstract]
Schedule of Investments	Our investments consisted of the following as of December 31, 2017 and 2016: As of December 31, 2017 Amortized Cost Gross Gains Gross Losses Estimated ($ in thousands) Money market funds $ 12,399 $ — $ — $ 12,399 Corporate notes 29,788 — (35 ) 29,753 Commercial paper 22,607 1 (25 ) 22,583 Total $ 64,794 $ 1 $ (60 ) $ 64,735 As of December 31, 2016 Amortized Cost Gross Gains Gross Losses Estimated ($ in thousands) Money market funds $ 35,218 $ — $ — $ 35,218 Corporate notes 22,347 — (7 ) 22,340 Commercial paper 33,633 7 (9 ) 33,631 Total $ 91,198 $ 7 $ (16 ) $ 91,189
Schedule of Fair Value of Investments	The fair values of our investments by classification in our consolidated balance sheets as of December 31, 2017 and 2016 were as follows: As of December 31, 2017 2016 ($ in thousands) Cash and cash equivalents $ 12,399 $ 35,218 Marketable securities 52,336 55,971 Total $ 64,735 $ 91,189

Fair Value Measurements and F31

Fair Value Measurements and Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements of Company's Financial Instruments	The following tables summarize the fair value measurements of our financial instruments as of December 31, 2017 and 2016: Fair Value Measurements at December 31, 2017 Quoted Prices in Active Markets Significant Observable Significant Unobservable Inputs (Level 3) Total ($ in thousands) Cash equivalents: Money market funds $ 12,399 $ — $ — $ 12,399 Total cash equivalents $ 12,399 $ — $ — $ 12,399 Marketable securities: Corporate notes $ — $ 29,753 $ — $ 29,753 Commercial paper — 22,583 — 22,583 Total marketable securities — 52,336 — 52,336 Total $ 12,399 $ 52,336 $ — $ 64,735 Fair Value Measurements at December 31, 2016 Quoted Prices in Active Markets Significant Observable Significant Unobservable Inputs (Level 3) Total ($ in thousands) Cash equivalents: Money market funds $ 35,218 $ — $ — $ 35,218 Total cash equivalents $ 35,218 $ — $ — $ 35,218 Marketable securities: Corporate notes $ — $ 22,340 $ — $ 22,340 Commercial paper — 33,631 — 33,631 Total marketable securities — 55,971 — 55,971 Total $ 35,218 $ 55,971 $ — $ 91,189

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Summary of Property and Equipment	Property and equipment consisted of the following as of December 31, 2017 and 2016: As of December 31, 2017 2016 ($ in thousands) Computer equipment and software $ 359 $ 406 Office furniture and equipment 173 593 Property and equipment, at cost 532 999 Less accumulated depreciation (339 ) (316 ) Property and equipment, net $ 193 $ 683

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following as of December 31, 2017 and 2016: As of December 31, 2017 2016 ($ in thousands) Accrued general and administrative expenses $ 752 $ 547 Accrued research and development expenses 2,501 2,107 Accrued payroll and employee benefits 780 2,597 Accrued restructuring costs — 283 Total accrued expenses $ 4,033 $ 5,534

Stock Incentive Plan (Tables)

Stock Incentive Plan (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Fair Value Calculation of Option Granted	The fair value of each stock option issued was estimated at the date of grant using the following weighted-average assumptions: For the Years 2017 2016 2015 Expected volatility 74 % 75 % 75 % Expected term (years) 5.69 6.22 6.26 Risk-free interest rate 1.81 % 1.45 % 1.71 % Expected dividend yield 0 % 0 % 0 %
Summary of Stock Option Activity	A summary of option activity as of December 31, 2017 and the year then ended is presented below: Number of Stock Options Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (Years) Aggregate Intrinsic Value Outstanding, January 1, 2017 3,652,801 $ 4.95 8.27 $ 779,340 Exercised (22,021 ) $ 0.09 Granted 116,750 $ 1.48 Forfeited/Expired (137,764 ) $ 9.18 Outstanding, December 31, 2017 3,609,766 $ 4.71 7.38 $ 668,434 Exercisable, December 31, 2017 2,250,316 $ 4.68 6.80 $ 632,034 Vested and expected to vest, December 31, 2017 3,609,766 $ 4.71 $ 7.38 $ 668,434
Schedule of Stock-based Compensation	Stock-based compensation expense for 2017, 2016 and 2015 consisted of the following: For the Years 2017 2016 2015 ($ in thousands) General and administrative $ 1,510 $ 1,717 $ 1,848 Research and development 2,012 1,629 1,410 Total $ 3,522 $ 3,346 $ 3,258

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Summary of Loss Before Provision for Income Taxes	Our loss before provision for income taxes for the years ended December 31, 2017, 2016 and 2015 consisted of the following: For the Years Ended December 31, 2017 2016 2015 ($ in thousands) Domestic $ (27,703 ) $ (61,390 ) $ (35,219 ) Foreign 287 626 (528 ) Total $ (27,416 ) $ (60,764 ) $ (35,747 )
Summary of Components of Income Tax Provision (Benefit)	The components of income tax provision (benefit) consisted of the following for the years ended December 31, 2017, 2016 and 2015: For the Years Ended December 31, 2017 2016 2015 ($ in thousands) Current provision for income taxes: U.S. $ 13 $ 12 $ — Foreign 281 351 191 Total current provision for income taxes 294 363 191 Deferred tax benefit - U.S. Federal (956 ) — — Deferred tax provision (benefit) - foreign 72 (16 ) (30 ) Total deferred benefit for income taxes (884 ) (16 ) (30 ) Total provision (benefit) for income taxes $ (590 ) $ 347 $ 161
Summary of Differences Between Effective Tax Rates and U.S. Federal Statutory Tax	A reconciliation setting forth the differences between our effective tax rates and the U.S. federal statutory tax rate is as follows: For the Years 2017 2016 2015 U.S. federal tax provision at statutory rate 34.00 % 34.00 % 34.00 % State and local tax, net of federal benefit 4.39 % 4.75 % 5.64 % Foreign rate differences 0.79 % 0.42 % 0.08 % Non-deductible foreign stock compensation (1.73 %) (0.63 %) (1.16 %) Effect of other permanent differences (0.66 %) (0.29 %) (0.05 %) Uncertain tax positions 0.13 % (0.03 %) (0.53 %) Change in valuation allowance 33.17 % (39.99 %) (37.74 %) Federal Tax Reform Rate Change (68.55 %) 0.00 % 0.00 % Other adjustments 0.62 % 1.16 % (0.69 %) Effective tax rate 2.16 % (0.61 %) (0.45 %)
Schedule of Components of Deferred Tax Assets and Liabilities	Significant components of our deferred tax assets and liabilities as of December 31, 2017 and 2016 are as follows: As of December 31, 2017 2016 ($ in thousands) Deferred tax assets: Federal and state net operating loss carryforwards $ 37,882 $ 44,778 Tax credit carryforwards — 1,024 Intangible and other related assets 312 347 Accrued expenses 627 1,826 Stock compensation 1,067 979 Other 120 251 Total deferred tax assets 40,008 49,205 Valuation allowance (39,984 ) (49,119 ) Net deferred tax assets $ 24 $ 86
Summary of Tax Years that Remain Subject to Examination	As of December 31, 2017, a summary of the tax years that remain subject to examination in our taxing jurisdictions is as follows: United States 2003 and forward Israel 2013 and forward
Reconciliation of Beginning and Ending Amount of Uncertain Tax Position	A reconciliation of the beginning and ending amount of our unrecognized tax benefits is as follows: For the Years 2017 2016 2015 ($ in thousands) Uncertain tax position at the beginning of year $ 460 $ 429 $ 241 Additions for uncertain tax positions of prior year 45 — — Additions for uncertain tax positions of current year — 40 188 Reductions for settlements with taxing authorities — — — Reductions for lapses of the applicable statutes of limitations (34 ) (9 ) — Uncertain tax position at the end of the year $ 471 $ 460 $ 429

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Rent Expense	Rent expense was as follows for 2017, 2016 and 2015: For the Years 2017 2016 2015 ($ in thousands) Rent Expense $ 945 $ 1,221 $ 347
Schedule of Minimum Rental Commitments for Operating Leases	At December 31, 2017, the minimum rental commitments under all non-cancelable operating leases with initial or remaining terms of more than one year, for each of the following fiscal years, are as follows: For the Years Ended December 31, 2018 2019 2020 2021 2022 Thereafter ($ in thousands) Operating Leases $ 156 $ 110 $ 104 $ — $ — $ —

Restructuring Charges (Tables)

Restructuring Charges (Tables)	12 Months Ended
	Dec. 31, 2017
Restructuring and Related Activities [Abstract]
Components of Restructuring Charges	The components of our restructuring charges are as follows: 2017 2016 ($ in thousands) Severance benefits and related costs $ — $ 2,211 Lease termination fees 1,038 — Non-cash restructuring charges — 1,474 Manufacturing suspension fees — 4,494 Total $ 1,038 $ 8,179
Activity Related to Accrued Restructuring Costs	Activity related to accrued restructuring costs is as follows: 2017 2016 ($ in thousands) Balance at beginning of year $ 283 $ — Plus: Current year restructuring costs 1,038 8,179 Less: Lease termination costs 1,038 — Payment of employee severance costs 283 1,928 Payment of manufacturing suspension fees — 4,494 Non-cash restructuring charges — 1,474 Balance at end of year $ — $ 283

Other Expenses (Income), net (T

Other Expenses (Income), net (Tables)	12 Months Ended
	Dec. 31, 2017
Other Income and Expenses [Abstract]
Summary of Other Expenses (Income), Net	Other expenses (income), net are as follows: For the Years 2017 2016 2015 ($ in thousands) Loss / (Gain) on foreign currency transactions, net $ 81 $ (9 ) $ — Interest income (928 ) (802 ) (128 ) Interest expense 131 264 349 Other expenses — — 79 Total $ (716 ) $ (547 ) $ 300

Quarterly Financial Data (una39

Quarterly Financial Data (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data	Three Months Ended March 31, 2017 June 30, 2017 September 30, 2017 December 31, 2017 ($ in thousands, except for per share data) Loss from operations $ (7,115 ) $ (6,920 ) $ (6,943 ) $ (7,154 ) Net loss (7,020 ) (6,854 ) (6,849 ) (6,103 ) Net loss attributable to common stockholders (7,020 ) (6,854 ) (6,849 ) (6,103 ) Earnings per share attributed to common stockholders - Basic $ (0.29 ) $ (0.28 ) $ (0.28 ) $ (0.25 ) Diluted $ (0.29 ) $ (0.28 ) $ (0.28 ) $ (0.25 ) Three Months Ended March 31, 2016 June 30, 2016 September 30, 2016 December 31, 2016 ($ in thousands, except for per share data) Loss from operations $ (17,220 ) $ (26,708 ) $ (9,439 ) $ (7,944 ) Net loss (17,180 ) (26,663 ) (9,373 ) (7,895 ) Net loss attributable to common stockholders (17,180 ) (26,663 ) (9,373 ) (7,895 ) Earnings per share attributed to common stockholders - Basic $ (0.71 ) $ (1.10 ) $ (0.38 ) $ (0.32 ) Diluted $ (0.71 ) $ (1.10 ) $ (0.38 ) $ (0.32 )

Nature of Business - Additional

Nature of Business - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017SubsidiariesPatient
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
Number of subsidiaries owned by the company | Subsidiaries	2
MPOWERED Trial [Member]
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
First trial period for adult acromegaly patients expected to randomize	6 months
Additional trial period for adult acromegaly patients expected to randomize	9 months
MPOWERED Trial [Member] | Maximum [Member]
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
Number of adult acromegaly patients expected to enroll in trial	130
Trial period for adult acromegaly patients expected to enroll	15 months
Number of adult acromegaly patients expect to randomize	80
CHIASMA OPTIMAL Trial [Member]
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
Number of adult acromegaly patients expected to enroll in trial	50
Trial period for adult acromegaly patients expected to enroll	9 months

Summary of Significant Accoun41

Summary of Significant Accounting Policies - Additional Information (Detail)	Jul. 21, 2015USD ($)$ / sharesshares	Dec. 31, 2017USD ($)Segment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
Sale of common stock, Per share | $ / shares	$ 16
Net proceeds from issue of shares	$ 106,500,000			$ 106,524,000
Reclassifications out of comprehensive income (loss)		$ 0	$ 0	0
Number of operating segments | Segment		1
Impairment of long-lived assets		$ 0	$ 0	$ 0
IPO [Member]
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
Sale of common stock, shares | shares	7,319,750
Sale of common stock, Per share | $ / shares	$ 16
Net proceeds from issue of shares	$ 106,500,000
Conversion of redeemable convertible preferred stock outstanding into common stock | shares	16,403,011

Summary of Significant Accoun42

Summary of Significant Accounting Policies - Schedule of Estimated Useful Lives of Assets (Detail)	12 Months Ended
	Dec. 31, 2017
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	The lesser of lease term or estimated useful lives
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Office Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	7 years
Office Furniture and Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	7 years
Office Furniture and Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	17 years
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	10 years
Laboratory Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	7 years
Laboratory Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	17 years

Investments - Schedule of Inves

Investments - Schedule of Investments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Gain (Loss) on Investments [Line Items]
Amortized Cost	$ 64,794	$ 91,198
Gross Unrealized Gains	1	7
Gross Unrealized Losses	(60)	(16)
Estimated Fair Value	64,735	91,189
Money Market Funds [Member]
Gain (Loss) on Investments [Line Items]
Amortized Cost	12,399	35,218
Estimated Fair Value	12,399	35,218
Corporate Notes [Member]
Gain (Loss) on Investments [Line Items]
Amortized Cost	29,788	22,347
Gross Unrealized Losses	(35)	(7)
Estimated Fair Value	29,753	22,340
Commercial Paper [Member]
Gain (Loss) on Investments [Line Items]
Amortized Cost	22,607	33,633
Gross Unrealized Gains	1	7
Gross Unrealized Losses	(25)	(9)
Estimated Fair Value	$ 22,583	$ 33,631

Investments - Additional Inform

Investments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments Schedule [Abstract]
Realized gains and losses on available-for-sale securities	$ 0	$ 0	$ 0
Cash excluded from cash and cash equivalents	$ 2,200,000	$ 1,800,000
Contractual maturity period of investments	1 year

Investments - Schedule of Fair

Investments - Schedule of Fair Value of Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Net Investment Income [Line Items]
Total	$ 64,735	$ 91,189
Cash and Cash Equivalents [Member]
Net Investment Income [Line Items]
Total	12,399	35,218
Marketable Securities [Member]
Net Investment Income [Line Items]
Total	$ 52,336	$ 55,971

Fair Value Measurements and F46

Fair Value Measurements and Fair Value of Financial Instruments - Fair Value Measurements of Company's Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Cash equivalents:
Total cash equivalents	$ 12,399	$ 35,218
Marketable securities:
Total marketable securities	64,735	91,189
Total	64,735	91,189
Corporate Notes [Member]
Marketable securities:
Total marketable securities	29,753	22,340
Marketable Securities [Member]
Marketable securities:
Total marketable securities	52,336	55,971
Commercial Paper [Member]
Marketable securities:
Total marketable securities	22,583	33,631
Money Market Funds [Member]
Cash equivalents:
Total cash equivalents	12,399	35,218
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Cash equivalents:
Total cash equivalents	12,399	35,218
Marketable securities:
Total	12,399	35,218
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Money Market Funds [Member]
Cash equivalents:
Total cash equivalents	12,399	35,218
Significant Other Observable Inputs (Level 2) [Member]
Marketable securities:
Total	52,336	55,971
Significant Other Observable Inputs (Level 2) [Member] | Corporate Notes [Member]
Marketable securities:
Total marketable securities	29,753	22,340
Significant Other Observable Inputs (Level 2) [Member] | Marketable Securities [Member]
Marketable securities:
Total marketable securities	52,336	55,971
Significant Other Observable Inputs (Level 2) [Member] | Commercial Paper [Member]
Marketable securities:
Total marketable securities	$ 22,583	$ 33,631

Fair Value Measurements and F47

Fair Value Measurements and Fair Value of Financial Instruments - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	$ 64,735	$ 91,189
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets fair value	$ 0	$ 0

Property and Equipment - Summar

Property and Equipment - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 532	$ 999
Less accumulated depreciation	(339)	(316)
Property and equipment, net	193	683
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	359	406
Office Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 173	$ 593

Property and Equipment - Additi

Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Depreciation	$ 152	$ 433	$ 201

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Accrued general and administrative expenses	$ 752	$ 547
Accrued research and development expenses	2,501	2,107
Accrued payroll and employee benefits	780	2,597
Accrued restructuring costs		283
Total accrued expenses	$ 4,033	$ 5,534

License Agreement - Additional

License Agreement - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended
	Mar. 15, 2018	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate amount of obligation				$ 5.1
Contractual obligation, first payment made		$ 1.7	$ 1.7
Subsequent Event [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contractual obligation, first payment made	$ 1.7

Warrants - Additional Informati

Warrants - Additional Information (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of Warrant or Right [Line Items]
Warrants outstanding	3,567,015		3,621,767
Warrants exercised	0	54,752
Minimum [Member]
Class of Warrant or Right [Line Items]
Warrants exercise price per share			$ 0.09
Warrants expiration date	Jun. 30, 2016
Maximum [Member]
Class of Warrant or Right [Line Items]
Warrants exercise price per share			$ 9.13
Warrants expiration date	Feb. 28, 2025

Redeemable Convertible Prefer53

Redeemable Convertible Preferred Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jul. 21, 2015	Feb. 28, 2015	Dec. 31, 2014	May 31, 2013	Dec. 31, 2015	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2017	Dec. 31, 2016
Temporary Equity [Line Items]
Gross proceeds from issuance of stock						$ 38,500	$ 38,500
Change in redemption value					$ 318
Sale of common stock, Per share	$ 16
Shares authorized for issuance								5,000,000	5,000,000
IPO [Member]
Temporary Equity [Line Items]
Sale of common stock, Per share	$ 16
Conversion of redeemable convertible preferred stock outstanding into common stock	16,403,011
Series D' Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Stock issuance, shares issued				38,504,439		38,504,439	38,504,439
Warrants purchasing common shares						1,698,066	1,698,066
Exercise price, common per share						$ 0.09	$ 0.09
Gross proceeds from issuance of stock						$ 34,800	$ 34,800
Issuance costs net						100	100
Additional amount required to redeem Series D preferred stock over original issuance cost				$ 38,500
Change in redemption value				38,500
Redemption of Series D redeemable convertible preferred stock for cash				$ 55,000
Series B1 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Stock issuance, shares issued				1,134,997
Series C' Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Stock issuance, shares issued				40,430,250
Series E Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Stock issuance, shares issued			33,774,763
Warrants purchasing common shares		984,116	924,622
Exercise price, common per share		$ 9.13	$ 9.13
Gross proceeds from issuance of stock		$ 35,900	$ 33,800
Issuance costs net		$ 300	$ 200
Sale of common stock, Per share		$ 1	$ 1
Net proceeds to warrant		$ 1,500	$ 800
Shares authorized for issuance		80,774,458
Issuance of convertible preferred stock		35,948,023			35,948,023
Series E Redeemable Convertible Preferred Stock [Member] | IPO [Member]
Temporary Equity [Line Items]
Conversion of redeemable convertible preferred stock outstanding into common stock	16,403,011
Warrant [Member]
Temporary Equity [Line Items]
Gross proceeds from issuance of stock						$ 3,600	$ 3,600

Common Stock - Additional Infor

Common Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jul. 21, 2015	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Common stock, shares issued	7,319,750		24,381,605	24,359,584
Common stock, par value	$ 0.01		$ 0.01	$ 0.01
Common stock, per share	$ 16
Net proceeds from issue of shares	$ 106,500	$ 106,524

Stock Incentive Plan - Addition

Stock Incentive Plan - Additional Information (Detail)	Jan. 01, 2018shares	Dec. 31, 2017USD ($)$ / sharesshares	Jan. 01, 2017shares	Jan. 01, 2016shares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)Directors$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock authorized for issuance		7,114,037			7,114,037
Shares of common stock available for grant		3,190,015			3,190,015
Number of stock option outstanding		3,609,766			3,609,766	3,652,801
Weighted average grant date fair value of stock options per share | $ / shares					$ 0.95	$ 4.38	$ 6.76
Aggregate intrinsic value of stock options exercised | $					$ 40,000	$ 3,500,000	$ 1,800,000
Unrecognized compensation cost related to stock options, expected to be recognized | $		$ 4,100,000			$ 4,100,000
Expected recognition, weighted-average period					2 years
Stock options exercised					22,021
Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value of stock options per share | $ / shares		$ 2.62
Stock options exercised							122,644
Liability, balance outstanding | $		$ 100,000			$ 100,000
Number of directors who exercised options to purchase common stock | Directors							2
Directors [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock, shares issued							116,258
Outstanding restricted shares		35,772			35,772
2008 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock authorized for issuance		3,547,741			3,547,741
2008 Plan [Member] | Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options expiration period					10 years
Stock options vesting period					4 years
2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock authorized for issuance		3,566,296			3,566,296
Increase in number of shares reserved and available for issuance	0		0	960,504
Percentage of shares issued and outstanding under plan				4.00%

Stock Incentive Plan - Schedule

Stock Incentive Plan - Schedule of Fair Value Calculation of Option Granted (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Expected volatility	74.00%	75.00%	75.00%
Expected term (years)	5 years 8 months 9 days	6 years 2 months 19 days	6 years 3 months 4 days
Risk-free interest rate	1.81%	1.45%	1.71%
Expected dividend yield	0.00%	0.00%	0.00%

Stock Incentive Plan - Summary

Stock Incentive Plan - Summary of Stock Option Activity (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Beginning balance	3,652,801
Number of stock options, Exercised	(22,021)
Number of stock options, Granted	116,750
Number of stock options, Forfeited/Expired	(137,764)
Ending balance	3,609,766	3,652,801
Number of stock options, Exercisable	2,250,316
Number of stock options, Vested and expected to vest	3,609,766
Weighted-average exercise price options outstanding, Beginning balance	$ 4.95
Weighted-average exercise price options, Exercised	0.09
Weighted-average exercise price options, Granted	1.48
Weighted-average exercise price options, Forfeited/Expired	9.18
Weighted-average exercise price options outstanding, Ending balance	4.71	$ 4.95
Weighted-average exercise price options, Exercisable	4.68
Weighted-average exercise price options, Vested and expected to vest	$ 4.71
Weighted- average remaining contractual term outstanding options	7 years 4 months 17 days	8 years 3 months 8 days
Weighted- average remaining contractual term options, Exercisable	6 years 9 months 18 days
Weighted- average remaining contractual term options, Vested and expected to vest	7 years 4 months 17 days
Aggregate Intrinsic Value options outstanding	$ 668,434	$ 779,340
Aggregate Intrinsic Value options, exercisable	632,034
Aggregate Intrinsic Value options, vested and expected to vest	$ 668,434

Stock Incentive Plan - Schedu58

Stock Incentive Plan - Schedule of Stock-based Compensation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock-based compensation expense:
Stock-based compensation expenses	$ 3,522	$ 3,346	$ 3,258
General and Administrative [Member]
Stock-based compensation expense:
Stock-based compensation expenses	1,510	1,717	1,848
Research and Development [Member]
Stock-based compensation expense:
Stock-based compensation expenses	$ 2,012	$ 1,629	$ 1,410

Income Taxes - Summary of Loss

Income Taxes - Summary of Loss Before Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Domestic	$ (27,703)	$ (61,390)	$ (35,219)
Foreign	287	626	(528)
Loss before income taxes	$ (27,416)	$ (60,764)	$ (35,747)

Income Taxes - Summary of Compo

Income Taxes - Summary of Components of Income Tax Provision (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current provision for income taxes:
U.S.	$ 13	$ 12
Foreign	281	351	$ 191
Total current provision for income taxes	294	363	191
Deferred tax benefit - U.S. Federal	(956)
Deferred tax provision (benefit) - foreign	72	(16)	(30)
Total deferred benefit for income taxes	(884)	(16)	(30)
Total provision (benefit) for income taxes	$ (590)	$ 347	$ 161

Income Taxes - Summary of Diffe

Income Taxes - Summary of Differences Between Effective Tax Rates and U.S. Federal Statutory Tax (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. federal tax provision at statutory rate	34.00%	34.00%	34.00%
State and local tax, net of federal benefit	4.39%	4.75%	5.64%
Foreign rate differences	0.79%	0.42%	0.08%
Non-deductible foreign stock compensation	(1.73%)	(0.63%)	(1.16%)
Effect of other permanent differences	(0.66%)	(0.29%)	(0.05%)
Uncertain tax positions	0.13%	(0.03%)	(0.53%)
Change in valuation allowance	33.17%	(39.99%)	(37.74%)
Federal Tax Reform Rate Change	(68.55%)	0.00%	0.00%
Other adjustments	0.62%	1.16%	(0.69%)
Effective tax rate	2.16%	(0.61%)	(0.45%)

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Federal and state net operating loss carryforwards	$ 37,882	$ 44,778
Tax credit carryforwards		1,024
Intangible and other related assets	312	347
Accrued expenses	627	1,826
Stock compensation	1,067	979
Other	120	251
Total deferred tax assets	40,008	49,205
Valuation allowance	(39,984)	(49,119)
Net deferred tax assets	$ 24	$ 86

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Increase in valuation allowance		$ (9,100,000)	$ 24,300,000
Federal tax rate		34.00%	34.00%	34.00%
Reduction in deferred tax asset		$ 18,800,000
U.S.Federal net operating loss carryforwards subject to annual limitation				$ 100,000
Effective income from non- research and development activities		2.16%	(0.61%)	(0.45%)
Unrecognized deferred tax liability		$ 300,000
Undistributed earnings of subsidiary		2,300,000
Scenario, Plan [Member]
Income Taxes [Line Items]
Federal tax rate	21.00%
Alternative Minimum Tax [Member]
Income Taxes [Line Items]
U.S.Federal alternative minimum tax credit carryforwards		1,000,000
Income tax receivable		$ 1,000,000
Maximum [Member]
Income Taxes [Line Items]
Federal tax rate		34.00%
Latest Tax Year [Member]
Income Taxes [Line Items]
Tax credit expiration period		Dec. 31, 2037
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		$ 113,100,000
United States [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		146,400,000
Non-US [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		$ 0
Israel [Member]
Income Taxes [Line Items]
Effective income tax rate on income from research and development activities		20.60%
Effective income from non- research and development activities		24.00%

Income Taxes - Summary of Tax Y

Income Taxes - Summary of Tax Years that Remain Subject to Examination (Detail)	12 Months Ended
	Dec. 31, 2017
2003 and Forward [Member] | United States [Member]
Income Tax Examination [Line Items]
Income tax examination	2003 and forward
2013 and Forward [Member] | Israel [Member]
Income Tax Examination [Line Items]
Income tax examination	2013 and forward

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Beginning and Ending Amount of Uncertain Tax Position (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Uncertain tax position at the beginning of year	$ 460	$ 429	$ 241
Additions for uncertain tax positions of prior year	45
Additions for uncertain tax positions of current year		40	188
Reductions for settlements with taxing authorities	0	0	0
Reductions for lapses of the applicable statutes of limitations	(34)	(9)
Uncertain tax position at the end of the year	$ 471	$ 460	$ 429

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Assets held under capital leases	$ 0	$ 0

Commitments and Contingencies67

Commitments and Contingencies - Schedule of Rent Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Leases, Rent Expense, Net [Abstract]
Rent Expense	$ 945	$ 1,221	$ 347

Commitments and Contingencies68

Commitments and Contingencies - Schedule of Future Minimum Rental Payments for Operating Leases (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Operating Leases, Future Minimum Payments Receivable [Abstract]
Operating Leases, minimum rental commitments, 2018	$ 156
Operating Leases, minimum rental commitments, 2019	110
Operating Leases, minimum rental commitments, 2020	104
Operating Leases, minimum rental commitments, 2021	0
Operating Leases, minimum rental commitments, 2022	0
Operating Leases, minimum rental commitments, Thereafter	$ 0

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Accrued liabilities	$ 4,033	$ 5,534
General and Administrative [Member]
Related Party Transaction [Line Items]
Expenses		200	$ 900
Head of Clinical [Member]
Related Party Transaction [Line Items]
Costs incurred for services	200	500	$ 400
Accrued liabilities	$ 100	$ 200

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Chiasma (Israel) Ltd [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employee benefit plans expense	$ 0.2	$ 0.5	$ 0.1

Restructuring Charges - Additio

Restructuring Charges - Additional Information (Detail) $ in Thousands	1 Months Ended		12 Months Ended
	Aug. 31, 2016	Jun. 30, 2016	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Nov. 30, 2017ft²
Restructuring Cost and Reserve [Line Items]
Lease termination fees			$ (1,038)
Total restructuring expenses			1,038	$ 8,179
Workforce reduction, percentage	44.00%	33.00%
Restructuring charges			1,038	8,179
Employee severance benefits and related costs				2,211
Non-cash restructuring charges				1,474
Impairment of leasehold improvements				1,700
Tenant allowances received under lease				900
Waltham MA Lease Facility [Member]
Restructuring Cost and Reserve [Line Items]
Area of terminated lease agreement | ft²					24,000
Lease termination fees			1,000
Write-off of office furniture and equipment			400
Deferred rent liabilities associated with terminated lease			400
Total restructuring expenses			$ 1,000
Manufacturing Suspension Fees [Member]
Restructuring Cost and Reserve [Line Items]
Payment of restructuring fees				4,494
Leasehold Improvements [Member]
Restructuring Cost and Reserve [Line Items]
Non-cash restructuring charges				800
Commercial Software and Laboratory Equipment [Member]
Restructuring Cost and Reserve [Line Items]
Non-cash restructuring charges				$ 700
Minimum [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reduction, percentage			60.00%

Restructuring Charges - Compone

Restructuring Charges - Components of Restructuring Charges (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Restructuring and Related Activities [Abstract]
Severance benefits and related costs		$ 2,211
Lease termination fees	$ 1,038
Non-cash restructuring charges		1,474
Manufacturing suspension fees		4,494
Total	$ 1,038	$ 8,179

Restructuring Charges - Activit

Restructuring Charges - Activity Related to Accrued Restructuring Costs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Balance at beginning of year	$ 283
Current year restructuring costs	1,038	$ 8,179
Lease termination costs	1,038
Non-cash restructuring charges		1,474
Balance at end of year		283
Employee Severance Costs [Member]
Restructuring Cost and Reserve [Line Items]
Payment of restructuring charges	$ 283	1,928
Manufacturing Suspension Fees [Member]
Restructuring Cost and Reserve [Line Items]
Payment of restructuring charges		$ 4,494

Other Expenses, Net - Summary o

Other Expenses, Net - Summary of Other Expenses (Income), Net (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Expense, Nonoperating [Abstract]
Loss / (Gain) on foreign currency transactions, net	$ 81	$ (9)
Interest income	(928)	(802)	$ (128)
Interest expense	131	264	349
Other expenses			79
Total	$ (716)	$ (547)	$ 300

Quarterly Financial Data (Una75

Quarterly Financial Data (Unaudited) - Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Data [Abstract]
Loss from operations	$ (7,154)	$ (6,943)	$ (6,920)	$ (7,115)	$ (7,944)	$ (9,439)	$ (26,708)	$ (17,220)	$ (28,132)	$ (61,311)	$ (35,447)
Net loss	(6,103)	(6,849)	(6,854)	(7,020)	(7,895)	(9,373)	(26,663)	(17,180)	(26,826)	(61,111)	(35,908)
Net loss attributable to common stockholders	$ (6,103)	$ (6,849)	$ (6,854)	$ (7,020)	$ (7,895)	$ (9,373)	$ (26,663)	$ (17,180)	$ (26,826)	$ (61,111)	$ (36,226)
Earnings per share attributed to common stockholders -
Basic	$ (0.25)	$ (0.28)	$ (0.28)	$ (0.29)	$ (0.32)	$ (0.38)	$ (1.10)	$ (0.71)	$ (1.10)	$ (2.51)	$ (3.25)
Diluted	$ (0.25)	$ (0.28)	$ (0.28)	$ (0.29)	$ (0.32)	$ (0.38)	$ (1.10)	$ (0.71)	$ (1.10)	$ (2.51)	$ (3.25)