Flexion Therapeutics (FLXN) 10-Q 8 May 15 2015 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2015	5-May-15
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	FALSE
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Trading Symbol	FLXN
Entity Registrant Name	Flexion Therapeutics Inc
Entity Central Index Key	1419600
Current Fiscal Year End Date	-19
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		21,461,419

Consolidated_Balance_Sheets_Un

Consolidated Balance Sheets (Unaudited) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$26,963,175	$103,097,522
Marketable securities	105,381,958	48,527,156
Accounts receivable	403,209
Prepaid expenses and other current assets	1,489,269	502,314
Total current assets	134,237,611	152,126,992
Property and equipment, net	1,663,980	1,109,391
Marketable securities	5,016,200
Other assets		12,375
Restricted cash	104,000	128,000
Total assets	141,021,791	153,376,758
Current liabilities:
Accounts payable	2,183,842	1,584,822
Accrued expenses and other current liabilities	1,975,832	3,213,704
Current portion of long-term debt		2,000,000
Total current liabilities	4,159,674	6,798,526
Long-term debt		1,593,333
Other long-term liabilities	28,234	43,008
Total liabilities	4,187,908	8,434,867
Commitments and contingencies
Preferred Stock, $.001 par value; 10,000,000 shares authorized at March 31, 2015 and December 31, 2014 and 0 shares issued and outstanding at March 31, 2015 and December 31, 2014
Stockholders' equity:
Common stock, $0.001 par value; 100,000,000 shares authorized; 21,461,419 and 21,440,058 shares issued and outstanding, at March 31, 2015 and December 31, 2014, respectively	21,461	21,440
Additional paid-in capital	239,447,573	238,402,514
Accumulated other comprehensive income	15,195	-5,240
Accumulated deficit	-102,650,346	-93,476,823
Total stockholders' equity	136,833,883	144,941,891
Total liabilities and stockholders' equity	$141,021,791	$153,376,758

Consolidated_Balance_Sheets_Un1

Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$0.00	$0.00
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	21,461,419	21,440,058
Common stock, shares outstanding	21,461,419	21,440,058

Consolidated_Statements_of_Ope

Consolidated Statements of Operations and Comprehensive Loss (Unaudited) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Income Statement [Abstract]
Revenue	$0	$0
Operating expenses:
Research and development	6,255,111	4,150,847
General and administrative	2,759,832	2,283,913
Total operating expenses	9,014,943	6,434,760
Loss from operations	-9,014,943	-6,434,760
Other income (expense):
Interest income	168,363	30,758
Interest expense	-203,468	-111,667
Other income (expense), net	-123,475	-26,575
Total other income (expense)	-158,580	-107,484
Net loss	-9,173,523	-6,542,244
Net loss per share basic and diluted	($0.43)	($0.86)
Weighted average common shares outstanding, basic and diluted	21,451,317	7,632,786
Other comprehensive (loss) income:
Unrealized gains from available-for-sale securities, net of tax of $0	20,435	842
Total other comprehensive income	20,435	842
Comprehensive loss	($9,153,088)	($6,541,402)

Consolidated_Statements_of_Ope1

Consolidated Statements of Operations and Comprehensive Loss (Unaudited) (Parenthetical) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Income Statement [Abstract]
Other comprehensive (loss) income, Tax	$0	$0

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (Unaudited) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Cash flows from operating activities
Net loss	($9,173,523)	($6,542,244)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation	39,680	27,344
Stock-based compensation expense	1,008,250	436,495
Amortization of premium (discount) on marketable securities	109,330	9,271
Other non-cash charges	12,375	4,125
Changes in operating assets and liabilities:
Accounts receivable	-403,209
Prepaid expenses, other current and long-term assets	-986,955	-663,202
Accounts payable	592,786	671,763
Accrued expenses and other current and long-term liabilities	-1,082,972	-430,366
Other	-93,333
Net cash used in operating activities	-9,977,571	-6,486,814
Cash flows from investing activities
Purchases of property and equipment	-533,060	-44,875
Change in restricted cash	24,000
Purchases of marketable securities	-89,424,898	-42,731,544
Redemption of marketable securities	27,465,000	250,000
Net cash used in investing activities	-62,468,958	-42,526,419
Cash flows from financing activities
Payment of public offering costs	-224,648	-1,096,588
Payments on debt	-3,500,000
Proceeds from the issuance of common stock		69,517,500
Proceeds from the exercise of stock options	36,830	193,312
Net cash (used in) provided by financing activities	-3,687,818	68,614,224
Net increase (decrease) in cash and cash equivalents	-76,134,347	19,600,991
Cash and cash equivalents at beginning of period	103,097,522	16,188,254
Cash and cash equivalents at end of period	26,963,175	35,789,245
Supplemental disclosures of cash flow information:
Cash paid for interest	292,037	100,000
Supplemental disclosures of non-cash financing activities:
Initial public offering costs included in accounts payable or accrued expenses		158,029
Conversion of convertible preferred stock into common stock		$74,806,213

Overview_and_Nature_of_the_Bus

Overview and Nature of the Business	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Overview and Nature of the Business	1	Overview and Nature of the Business
	Flexion Therapeutics, Inc. (“Flexion” or the “Company”) was incorporated under the laws of the state of Delaware on November 5, 2007. Flexion is a specialty pharmaceutical company focused on the development and commercialization of novel, injectable pain therapies. The Company is targeting anti-inflammatory and analgesic therapies for the treatment of patients with musculoskeletal conditions, beginning with osteoarthritis, a type of degenerative arthritis (“OA”) and post-operative pain. Flexion’s broad and diversified portfolio of product candidates addresses the OA pain treatment spectrum, from moderate to severe pain, and provides the Company with multiple opportunities to achieve its goal of commercializing novel, patient-focused pain therapies.
	The Company is subject to risks and uncertainties common to companies in the biopharmaceutical industry, including, but not limited to, new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations, and ability to secure additional capital to fund operations. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel infrastructure and extensive compliance reporting capabilities. The Company’s product candidates are all in the development stage. There can be no assurance that development efforts, including clinical trials, will be successful. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales.

Summary_of_Significant_Account

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2	Summary of Significant Accounting Policies
	Basis of Presentation
	The accompanying condensed consolidated financial statements as of March 31, 2015, and for the three months ended March 31, 2015 and 2014, have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (the “SEC”) and Generally Accepted Accounting Principles (‘GAAP”) for consolidated financial information including the accounts of the Company and its wholly-owned subsidiary after elimination of all significant intercompany accounts and transactions. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, these condensed consolidated financial statements reflect all adjustments which are necessary for a fair statement of the Company’s financial position and results of its operations, as of and for the periods presented. These condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K filed with the SEC on March 24, 2015.
	The information presented in the condensed consolidated financial statements and related notes as of March 31, 2015, and for the three months ended March 31, 2015 and 2014, is unaudited. The December 31, 2014 consolidated balance sheet included herein was derived from the audited financial statements as of that date, but does not include all disclosures, including notes, required by GAAP for complete financial statements.
	Interim results for the three months ended March 31, 2015 are not necessarily indicative of the results that may be expected for the fiscal year ending December 31, 2015, or any future period.
	The accompanying condensed consolidated financial statements have been prepared on a basis which assumes that the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the normal course of business. The Company has incurred recurring losses and negative cash flows from operations. As of March 31, 2015 and December 31, 2014, the Company had cash and cash equivalents and marketable securities of $137,361,333 and $151,624,678, respectively. Management believes that current cash, cash equivalents and marketable securities on hand at March 31, 2015 should be sufficient to fund operations for at least the next twelve months. The future viability of the Company is dependent on its ability to raise additional capital to finance its operations and to fund increased research and development costs in order to seek approval for commercialization of its product candidates. The Company’s failure to raise capital as and when needed would have a negative impact on its financial condition and its ability to pursue its business strategies as this capital is necessary for the Company to perform the research and development activities required to develop the Company’s product candidates in order to generate future revenue streams.
	Consolidation
	The accompanying condensed consolidated financial statements include the Company and its wholly-owned subsidiary, Flexion Securities Corporation, Inc. The Company has eliminated all intercompany transactions for the three months ended March 31, 2015 and the year ended December 31, 2014, the year Flexion Securities Corporation, Inc. was established.
	U.S. Government Grant
	The Company performs research and development for a U.S. Government agency under a cost reimbursable grant for clinical development of FX006. The related costs incurred under the grant are included in research and development expense in the statements of operations. The Company is reimbursed and offsets research and development expenses in the statement of operations when invoices for allowable costs are prepared and submitted to the U.S. Government agency. Payments under cost reimbursable grants with agencies of the U.S. Government are provisional payments subject to adjustment upon audit by the U.S. government. When the final determination of the allowable costs for any year has been made, research and development expenses may be adjusted accordingly. The grant also provides the U.S. government agency the ability to terminate the grant for various reasons, including if we fail to meet our obligations as set forth in the grant.
	Accounts Receivable
	Accounts receivable represents allowable costs under the Company’s U.S. Government agency grant for which the Company has not yet received reimbursement. The Company invoices the government on a quarterly basis for reimbursable costs under the grant. Reimbursable costs that have not been invoiced on the last day of the quarter are recorded as unbilled accounts receivable.
	Use of Estimates
	The preparation of financial statements in conformity with GAAP requires management to make estimates and judgments that may affect the reported amounts of assets and liabilities, expenses and related disclosures. The Company bases estimates and judgments on historical experience and on various other factors that it believes to be reasonable under the circumstances. The most significant estimates in these condensed consolidated financial statements include useful lives with respect to long-lived assets, such as property and equipment and leasehold improvements, accounting for stock-based compensation, and accrued expenses, including clinical research costs. The Company’s actual results may differ from these estimates under different assumptions or conditions. The Company evaluates its estimates on an ongoing basis. Changes in estimates are reflected in reported results in the period in which they become known by the Company’s management.

Fair_Value_of_Financial_Assets

Fair Value of Financial Assets	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets	3	Fair Value of Financial Assets
	The following tables present information about the Company’s assets and liabilities that are measured at fair value on a recurring basis as of March 31, 2015 and December 31, 2014 and indicate the level of the fair value hierarchy utilized to determine such fair value:
			Fair Value Measurements as of March 31, 2015 Using:
			Level 1		Level 2		Level 3		Total
	Assets:
	Cash equivalents		$	—	$	24,628,158	$	—	$	24,628,158
	Marketable securities			—		110,398,158		—		110,398,158
			$	—	$	135,026,316	$	—	$	135,026,316
			Fair Value Measurements as of December 31, 2014 Using:
			Level 1		Level 2		Level 3		Total
	Assets:
	Cash equivalents		$	—	$	101,687,995	$	—	$	101,687,995
	Marketable securities			—		48,527,156		—		48,527,156
			$	—	$	150,215,151	$	—	$	150,215,151
	As of March 31, 2015 and December 31, 2014, the Company’s cash equivalents and marketable securities that were invested primarily in U.S. treasury bills, corporate bonds, money market funds, commercial paper and U.S. Government agency holdings were valued based primarily on Level 2 inputs. The Company measures the fair value of marketable securities using Level 2 inputs and primarily relies on quoted prices in active markets for similar marketable securities. During the three months ended March 31, 2015 and year ended December 31, 2014, there were no transfers between Level 1, Level 2 and Level 3.
	The carrying values of accounts receivable, accounts payable and accrued expenses approximate their fair value due to the short-term nature of these balances.

Marketable_Securities

Marketable Securities	3 Months Ended
	Mar. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	4	Marketable Securities
	As of March 31, 2015 and December 31, 2014, the fair value of available-for-sale marketable securities by type of security was as follows:
			March 31, 2015
			Amortized Cost		Gross Unrealized		Gross Unrealized			Fair Value
					Gains		Losses
	Commercial paper		$	23,719,268	$	26,992	$	—		$	23,746,260
	U.S. Government Obligations			13,080,203		644		(198	)		13,080,649
	Corporate bonds			73,583,492		8,966		(21,209	)		73,571,249
			$	110,382,963	$	36,602	$	(21,407	)	$	110,398,158
			December 31, 2014
			Amortized Cost		Gross Unrealized		Gross Unrealized			Fair Value
					Gains		Losses
	Commercial paper		$	8,991,820	$	7,570	$	—		$	8,999,390
	U.S. Government Obligations			28,300,921		181		(5,101	)		28,296,001
	Corporate bonds			11,239,655		2		(7,892	)		11,231,765
			$	48,532,396	$	7,753	$	(12,993	)	$	48,527,156
	At March 31, 2015 and December 31, 2014, marketable securities consisted of investments that mature within 14 months and twelve months, respectively. The estimated fair value and amortized cost of the Company’s marketable debt securities available-for-sale by contractual maturity are summarized as follows:
			As of March 31, 2015				As of December 31, 2014
			Fair Value		Amortized Cost		Fair Value			Amortized Cost
	Due in one year of less		$	105,381,958	$	105,370,385	$	48,527,156		$	48,532,396
	Due after one year through 5 years			5,016,200		5,012,578		—			—
	Total available-for-sale securities		$	110,398,158	$	110,382,963	$	48,527,156		$	48,532,396

Property_and_Equipment

Property and Equipment	3 Months Ended
	Mar. 31, 2015
Property, Plant and Equipment [Abstract]
Property and Equipment	5	Property and Equipment
	Property and equipment as of March 31, 2015 and December 31, 2014 consisted of the following:
			March 31,			December 31,
			2015			2014
	Computer and office equipment		$	251,386		$	229,980
	Manufacturing equipment			153,140			153,140
	Furniture and fixtures			181,366			181,366
	Software			98,869			77,454
	Leasehold improvements			134,573			134,573
	Construction—in Progress			1,152,765			601,317
				1,972,099			1,377,830
	Less: Accumulated depreciation			(308,119	)		(268,439	)
	Total property and equipment, net		$	1,663,980		$	1,109,391
	Depreciation expense for the three months ended March 31, 2015 and, 2014, was $39,680 and $27,344, respectively. During the three months ended March 31, 2015 and 2014, there were no disposals of property and equipment.

Accrued_Expenses_and_Other_Cur

Accrued Expenses and Other Current Liabilities	3 Months Ended
	Mar. 31, 2015
Payables and Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	6	Accrued Expenses and Other Current Liabilities
	Accrued expenses and other current liabilities consisted of the following:
			March 31,		December 31,
			2015		2014
	Clinical research		$	582,650	$	1,035,510
	Contract manufacturing services			270,000		294,900
	Payroll and other employee-related expenses			649,205		1,172,978
	Preclinical services			—		119,500
	Consultant fees and expenses			74,150		26,900
	Professional services fees			325,333		439,874
	Interest expense			—		24,111
	Other			74,494		99,931
	Total accrued expenses and other current liabilities		$	1,975,832	$	3,213,704

StockBased_Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	7	Stock-Based Compensation
	Stock Option Valuation
	The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. Prior to the IPO, the Company was a private company and therefore lacked company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of its publicly-traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain vanilla” options. The expected term of stock options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. The relevant data used to determine the value of the stock option grants for the three months ended March 31, 2015 and 2014 are as follows:
			Three months ended
			March 31,
			2015			2014
	Risk-free interest rates			1.51-1.83	%		1.54-1.87	%
	Expected dividend yield			0	%		0	%
	Expected term (in years)			6			6
	Expected volatility			78.4-81.4	%		64.3-66.9	%
	The following table summarizes stock option activity for the three months ended March 31, 2015:
			Shares			Weighted
			Issuable			Average
			Under			Exercise
			Options			Price
	Outstanding as of December 31, 2014			1,289,082		$	10.26
	Granted			397,425			23.27
	Exercised			(21,361	)		1.74
	Canceled			(28,336	)		17.23
	Outstanding as of March 31, 2015			1,636,810		$	13.41
	Options vested and expected to vest at March 31, 2015			1,387,913
	Options exercisable at March 31, 2015			581,956
	The aggregate intrinsic value of options is calculated as the difference between the exercise price of the options and the fair value of the Company’s common stock for those options that had exercise prices lower than the fair value of the Company’s common stock. A total of 21,361 options were exercised during the three months ended March 31, 2015. The aggregate intrinsic value of stock options exercised during the three months ended March 31, 2015 was $456,078.
	At March 31, 2015 and 2014 the Company had options for the purchase of 1,636,810 and 1,190,704 shares of common stock outstanding, respectively, with a weighted average remaining contractual term of 8.4, and 8.7 years, respectively, and with a weighted average exercise price of $13.41 and $9.54 per share, respectively.
	The weighted average grant date fair value of options granted during the three months ended March 31, 2015 and 2014 was $23.27 and $10.49, respectively.
	Stock-based Compensation
	The Company recorded stock-based compensation expense related to stock options for the three months ended March 31, 2015 and 2014 as follows:
			Three months ended,
			2015			2014
	Research and development		$	321,749		$	113,518
	General and administrative			686,501			322,977
			$	1,008,250		$	436,495
	As of March 31, 2015, unrecognized stock-based compensation expense for stock options outstanding was $12,643,020, which is expected to be recognized over a weighted average period of 3.2 years. As of March 31, 2014, unrecognized stock-based compensation expense for stock options outstanding was $7,717,771, which was expected to be recognized over a weighted average period of 3.3 years.

Net_Loss_Per_Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Net Loss Per Share	8	Net Loss Per Share
	Basic and diluted net loss per share attributable to common stockholders was calculated as follows for the three months ended March 31, 2015 and 2014:
			2015			2014
	Numerator:
	Net loss		$	(9,173,523	)	$	(6,542,244	)
	Net loss:		$	(9,173,523	)	$	(6,542,244	)
	Denominator:
	Weighted average common shares outstanding, basic and diluted			21,451,317			7,632,786
	Net loss per share, basic and diluted		$	(0.43	)	$	(0.86	)
	Stock options for the purchase of 1,548,014 and 942,165 weighted average shares of common stock were excluded from the computation of diluted net loss per share attributable to common stockholders for the three months ended March 31, 2015 and 2014, respectively, because those options had an anti-dilutive impact due to the net loss incurred for those periods. These options were excluded from the computations because they had an anti-dilutive impact to diluted net loss attributable to common stockholders incurred for those periods.

Longterm_Debt

Long-term Debt	3 Months Ended
	Mar. 31, 2015
Debt Disclosure [Abstract]
Long-term Debt	9	Long-term Debt
	On January 3, 2013, the Company entered into a credit and security agreement with MidCap Financial SBIC, LP (“MidCap”) under which it immediately borrowed $5,000,000 as a term loan. The term loan accrued interest monthly at an interest rate of 8.0% per annum and had a term of 45 months. As the term loan had a 15-month interest-only period, the term loan principal balance, along with any accrued interest, was to be paid in 30 equal monthly installments beginning April 1, 2014 and ending September 1, 2016. In addition to these principal payments, the Company was required to make a payment of $175,000 to the lender on September 1, 2016, which amount was accreted to the carrying value of the debt using the effective interest rate method. On March 31, 2015, the Company paid MidCap $3,236,019, representing the outstanding principal of the debt along with accrued interest as of that date, the $175,000 final payment, a prepayment fee of $30,000 and associated legal expenses to satisfy the Company’s obligation under the credit and security agreement.
	Prior to the debt repayment, the term loan outstanding under the Company’s credit and security agreement with MidCap was reported at its carrying value in the accompanying balance sheet. The Company determined the fair value of the term loan using an income approach, utilizing a discounted cash flow analysis based on current market interest rates for debt issuances with similar remaining years to maturity, adjusted for credit risk. The term loan was valued using Level 2 inputs as of December 31, 2014. The result of the calculation yielded a fair value that approximates carrying value.

Subsequent_Events

Subsequent Events	3 Months Ended
	Mar. 31, 2015
Subsequent Events [Abstract]
Subsequent Events	10	Subsequent Events
	There were no subsequent events that require disclosure in the financial statements for the period ended March 31, 2015.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation
	The accompanying condensed consolidated financial statements as of March 31, 2015, and for the three months ended March 31, 2015 and 2014, have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (the “SEC”) and Generally Accepted Accounting Principles (‘GAAP”) for consolidated financial information including the accounts of the Company and its wholly-owned subsidiary after elimination of all significant intercompany accounts and transactions. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, these condensed consolidated financial statements reflect all adjustments which are necessary for a fair statement of the Company’s financial position and results of its operations, as of and for the periods presented. These condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K filed with the SEC on March 24, 2015.
	The information presented in the condensed consolidated financial statements and related notes as of March 31, 2015, and for the three months ended March 31, 2015 and 2014, is unaudited. The December 31, 2014 consolidated balance sheet included herein was derived from the audited financial statements as of that date, but does not include all disclosures, including notes, required by GAAP for complete financial statements.
	Interim results for the three months ended March 31, 2015 are not necessarily indicative of the results that may be expected for the fiscal year ending December 31, 2015, or any future period.
	The accompanying condensed consolidated financial statements have been prepared on a basis which assumes that the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the normal course of business. The Company has incurred recurring losses and negative cash flows from operations. As of March 31, 2015 and December 31, 2014, the Company had cash and cash equivalents and marketable securities of $137,361,333 and $151,624,678, respectively. Management believes that current cash, cash equivalents and marketable securities on hand at March 31, 2015 should be sufficient to fund operations for at least the next twelve months. The future viability of the Company is dependent on its ability to raise additional capital to finance its operations and to fund increased research and development costs in order to seek approval for commercialization of its product candidates. The Company’s failure to raise capital as and when needed would have a negative impact on its financial condition and its ability to pursue its business strategies as this capital is necessary for the Company to perform the research and development activities required to develop the Company’s product candidates in order to generate future revenue streams.
Consolidation	Consolidation
	The accompanying condensed consolidated financial statements include the Company and its wholly-owned subsidiary, Flexion Securities Corporation, Inc. The Company has eliminated all intercompany transactions for the three months ended March 31, 2015 and the year ended December 31, 2014, the year Flexion Securities Corporation, Inc. was established.
U.S. Government Grant	U.S. Government Grant
	The Company performs research and development for a U.S. Government agency under a cost reimbursable grant for clinical development of FX006. The related costs incurred under the grant are included in research and development expense in the statements of operations. The Company is reimbursed and offsets research and development expenses in the statement of operations when invoices for allowable costs are prepared and submitted to the U.S. Government agency. Payments under cost reimbursable grants with agencies of the U.S. Government are provisional payments subject to adjustment upon audit by the U.S. government. When the final determination of the allowable costs for any year has been made, research and development expenses may be adjusted accordingly. The grant also provides the U.S. government agency the ability to terminate the grant for various reasons, including if we fail to meet our obligations as set forth in the grant.
Accounts Receivable	Accounts Receivable
	Accounts receivable represents allowable costs under the Company’s U.S. Government agency grant for which the Company has not yet received reimbursement. The Company invoices the government on a quarterly basis for reimbursable costs under the grant. Reimbursable costs that have not been invoiced on the last day of the quarter are recorded as unbilled accounts receivable.
Use of Estimates	Use of Estimates
	The preparation of financial statements in conformity with GAAP requires management to make estimates and judgments that may affect the reported amounts of assets and liabilities, expenses and related disclosures. The Company bases estimates and judgments on historical experience and on various other factors that it believes to be reasonable under the circumstances. The most significant estimates in these condensed consolidated financial statements include useful lives with respect to long-lived assets, such as property and equipment and leasehold improvements, accounting for stock-based compensation, and accrued expenses, including clinical research costs. The Company’s actual results may differ from these estimates under different assumptions or conditions. The Company evaluates its estimates on an ongoing basis. Changes in estimates are reflected in reported results in the period in which they become known by the Company’s management.

Fair_Value_of_Financial_Assets1

Fair Value of Financial Assets (Tables)	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis	The following tables present information about the Company’s assets and liabilities that are measured at fair value on a recurring basis as of March 31, 2015 and December 31, 2014 and indicate the level of the fair value hierarchy utilized to determine such fair value:
		Fair Value Measurements as of March 31, 2015 Using:
		Level 1		Level 2		Level 3		Total
	Assets:
	Cash equivalents	$	—	$	24,628,158	$	—	$	24,628,158
	Marketable securities		—		110,398,158		—		110,398,158
		$	—	$	135,026,316	$	—	$	135,026,316
		Fair Value Measurements as of December 31, 2014 Using:
		Level 1		Level 2		Level 3		Total
	Assets:
	Cash equivalents	$	—	$	101,687,995	$	—	$	101,687,995
	Marketable securities		—		48,527,156		—		48,527,156
		$	—	$	150,215,151	$	—	$	150,215,151

Marketable_Securities_Tables

Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Summary of Fair Value of Available-for-Sale Marketable Securities by Type of Security	As of March 31, 2015 and December 31, 2014, the fair value of available-for-sale marketable securities by type of security was as follows:
		March 31, 2015
		Amortized Cost		Gross Unrealized		Gross Unrealized			Fair Value
				Gains		Losses
	Commercial paper	$	23,719,268	$	26,992	$	—		$	23,746,260
	U.S. Government Obligations		13,080,203		644		(198	)		13,080,649
	Corporate bonds		73,583,492		8,966		(21,209	)		73,571,249
		$	110,382,963	$	36,602	$	(21,407	)	$	110,398,158
		December 31, 2014
		Amortized Cost		Gross Unrealized		Gross Unrealized			Fair Value
				Gains		Losses
	Commercial paper	$	8,991,820	$	7,570	$	—		$	8,999,390
	U.S. Government Obligations		28,300,921		181		(5,101	)		28,296,001
	Corporate bonds		11,239,655		2		(7,892	)		11,231,765
		$	48,532,396	$	7,753	$	(12,993	)	$	48,527,156
Summary of Estimated Fair Value and Amortized Cost of Marketable Debt Securities Available-for-Sale by Contractual Maturity	The estimated fair value and amortized cost of the Company’s marketable debt securities available-for-sale by contractual maturity are summarized as follows:
		As of March 31, 2015				As of December 31, 2014
		Fair Value		Amortized Cost		Fair Value			Amortized Cost
	Due in one year of less	$	105,381,958	$	105,370,385	$	48,527,156		$	48,532,396
	Due after one year through 5 years		5,016,200		5,012,578		—			—
	Total available-for-sale securities	$	110,398,158	$	110,382,963	$	48,527,156		$	48,532,396

Property_and_Equipment_Tables

Property and Equipment (Tables)	3 Months Ended
	Mar. 31, 2015
Property, Plant and Equipment [Abstract]
Components of Property and Equipment	Property and equipment as of March 31, 2015 and December 31, 2014 consisted of the following:
		March 31,			December 31,
		2015			2014
	Computer and office equipment	$	251,386		$	229,980
	Manufacturing equipment		153,140			153,140
	Furniture and fixtures		181,366			181,366
	Software		98,869			77,454
	Leasehold improvements		134,573			134,573
	Construction—in Progress		1,152,765			601,317
			1,972,099			1,377,830
	Less: Accumulated depreciation		(308,119	)		(268,439	)
	Total property and equipment, net	$	1,663,980		$	1,109,391

Accrued_Expenses_and_Other_Cur1

Accrued Expenses and Other Current Liabilities (Tables)	3 Months Ended
	Mar. 31, 2015
Payables and Accruals [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following:
		March 31,		December 31,
		2015		2014
	Clinical research	$	582,650	$	1,035,510
	Contract manufacturing services		270,000		294,900
	Payroll and other employee-related expenses		649,205		1,172,978
	Preclinical services		—		119,500
	Consultant fees and expenses		74,150		26,900
	Professional services fees		325,333		439,874
	Interest expense		—		24,111
	Other		74,494		99,931
	Total accrued expenses and other current liabilities	$	1,975,832	$	3,213,704

StockBased_Compensation_Tables

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Relevant Data Used to Estimate Fair Value of Stock Option Grants	The relevant data used to determine the value of the stock option grants for the three months ended March 31, 2015 and 2014 are as follows:
		Three months ended
		March 31,
		2015			2014
	Risk-free interest rates		1.51-1.83	%		1.54-1.87	%
	Expected dividend yield		0	%		0	%
	Expected term (in years)		6			6
	Expected volatility		78.4-81.4	%		64.3-66.9	%
Summary of Stock Option Activity	The following table summarizes stock option activity for the three months ended March 31, 2015:
		Shares			Weighted
		Issuable			Average
		Under			Exercise
		Options			Price
	Outstanding as of December 31, 2014		1,289,082		$	10.26
	Granted		397,425			23.27
	Exercised		(21,361	)		1.74
	Canceled		(28,336	)		17.23
	Outstanding as of March 31, 2015		1,636,810		$	13.41
	Options vested and expected to vest at March 31, 2015		1,387,913
	Options exercisable at March 31, 2015		581,956
Stock-Based Compensation Expense Related to Stock Options	The Company recorded stock-based compensation expense related to stock options for the three months ended March 31, 2015 and 2014 as follows:
		Three months ended,
		2015			2014
	Research and development	$	321,749		$	113,518
	General and administrative		686,501			322,977
		$	1,008,250		$	436,495

Net_Loss_Per_Share_Tables

Net Loss Per Share (Tables)	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Net Loss per Share Attributable to Common Stockholders	Basic and diluted net loss per share attributable to common stockholders was calculated as follows for the three months ended March 31, 2015 and 2014:
		2015			2014
	Numerator:
	Net loss	$	(9,173,523	)	$	(6,542,244	)
	Net loss:	$	(9,173,523	)	$	(6,542,244	)
	Denominator:
	Weighted average common shares outstanding, basic and diluted		21,451,317			7,632,786
	Net loss per share, basic and diluted	$	(0.43	)	$	(0.86	)

Overview_and_Nature_of_the_Bus1

Overview and Nature of the Business - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Incorporation date	5-Nov-07

Summary_of_Significant_Account2

Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Cash and cash equivalents and marketable securities	$137,361,333	$151,624,678

Fair_Value_of_Financial_Assets2

Fair Value of Financial Assets - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$110,398,158	$48,527,156
Fair Value Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	24,628,158	101,687,995
Marketable securities	110,398,158	48,527,156
Assets, Total	135,026,316	150,215,151
Level 2 [Member] | Fair Value Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	24,628,158	101,687,995
Marketable securities	110,398,158	48,527,156
Assets, Total	$135,026,316	$150,215,151

Fair_Value_of_Financial_Assets3

Fair Value of Financial Assets - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Transfers between Level 1, Level 2 and Level 3	$0	$0

Marketable_Securities_Summary_

Marketable Securities - Summary of Fair Value of Available-for-Sale Marketable Securities by Type of Security (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$110,382,963	$48,532,396
Gross Unrealized Gains	36,602	7,753
Gross Unrealized Losses	-21,407	-12,993
Fair Value	110,398,158	48,527,156
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,719,268	8,991,820
Gross Unrealized Gains	26,992	7,570
Fair Value	23,746,260	8,999,390
U.S Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,080,203	28,300,921
Gross Unrealized Gains	644	181
Gross Unrealized Losses	-198	-5,101
Fair Value	13,080,649	28,296,001
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	73,583,492	11,239,655
Gross Unrealized Gains	8,966	2
Gross Unrealized Losses	-21,209	-7,892
Fair Value	$73,571,249	$11,231,765

Marketable_Securities_Addition

Marketable Securities - Additional Information (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Maturity period of investment	14 months	12 months

Marketable_Securities_Summary_1

Marketable Securities - Summary of Estimated Fair Value and Amortized Cost of Marketable Debt Securities Available-for-Sale by Contractual Maturity (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Disclosure Schedule Of Available For Sale Marketable Securities [Abstract]
Due in one year of less, Fair Value	$105,381,958	$48,527,156
Due after one year through 5 years, Fair Value	5,016,200
Total available-for-sale securities, Fair Value	110,398,158	48,527,156
Due in one year of less, Amortized Cost	105,370,385	48,532,396
Due after one year through 5 years, Amortized Cost	5,012,578
Total available-for-sale securities, Amortized Cost	$110,382,963	$48,532,396

Property_and_Equipment_Compone

Property and Equipment - Components of Property and Equipment (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and equipment gross	$1,972,099	$1,377,830
Less: Accumulated depreciation	-308,119	-268,439
Total property and equipment, net	1,663,980	1,109,391
Computer and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	251,386	229,980
Manufacturing Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	153,140	153,140
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	181,366	181,366
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	134,573	134,573
Construction-in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	1,152,765	601,317
Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	$98,869	$77,454

Property_and_Equipment_Additio

Property and Equipment - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Property, Plant and Equipment [Abstract]
Depreciation	$39,680	$27,344
Property and equipment disposals	$0	$0

Accrued_Expenses_and_Other_Cur2

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Payables and Accruals [Abstract]
Clinical research	$582,650	$1,035,510
Contract manufacturing services	270,000	294,900
Payroll and other employee-related expenses	649,205	1,172,978
Preclinical services		119,500
Consultant fees and expenses	74,150	26,900
Professional services fees	325,333	439,874
Interest expense		24,111
Other	74,494	99,931
Total accrued expenses and other current liabilities	$1,975,832	$3,213,704

StockBased_Compensation_Schedu

Stock-Based Compensation - Schedule of Relevant Data Used to Estimate Fair Value of Stock Option Grants (Detail)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk-free interest rates, Minimum	1.51%	1.54%
Risk-free interest rates, Maximum	1.83%	1.87%
Expected dividend yield	0.00%	0.00%
Expected term (in years)	6 years	6 years
Expected volatility, Minimum	78.40%	64.30%
Expected volatility, Maximum	81.40%	66.90%

StockBased_Compensation_Summar

Stock-Based Compensation - Summary of Stock Option Activity (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares Issuable Under Options, Beginning balance	1,289,082	1,190,704
Shares Issuable Under Options, Granted	397,425
Shares Issuable Under Options, Exercised	-21,361
Shares Issuable Under Options, Canceled	-28,336
Shares Issuable Under Options, Ending balance	1,636,810	1,190,704
Shares Issuable Under Options, Options vested and expected to vest at March 31, 2015	1,387,913
Shares Issuable Under Options, Options exercisable at March 31, 2015	581,956
Weighted Average Exercise Price, Beginning balance	$10.26	$9.54
Weighted Average Exercise Price, Granted	$23.27
Weighted Average Exercise Price, Exercised	$1.74
Weighted Average Exercise Price, Canceled	$17.23
Weighted Average Exercise Price, Ending balance	$13.41	$9.54

StockBased_Compensation_Additi

Stock-Based Compensation - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of options exercised	21,361
Aggregate intrinsic value of stock options exercised	$456,078
Options to purchase common stock, outstanding	1,636,810	1,190,704	1,289,082
Weighted average remaining contractual term	8 years 4 months 24 days	8 years 8 months 12 days
Weighted average exercise price	$13.41	$9.54	$10.26
Weighted average grant date fair value of options granted	$23.27	$10.49
Unrecognized stock-based compensation expense	$12,643,020	$7,717,771
Stock options recognized over weighted average period	3 years 2 months 12 days	3 years 3 months 18 days

StockBased_Compensation_StockB

Stock-Based Compensation - Stock-Based Compensation Expense Related to Stock Options (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$1,008,250	$436,495
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	321,749	113,518
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$686,501	$322,977

Net_Loss_Per_Share_Schedule_of

Net Loss Per Share - Schedule of Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Numerator:
Net loss	($9,173,523)	($6,542,244)
Net loss:	($9,173,523)	($6,542,244)
Denominator:
Weighted average common shares outstanding, basic and diluted	21,451,317	7,632,786
Net loss per share, basic and diluted	($0.43)	($0.86)

Net_Loss_Per_Share_Additional_

Net Loss Per Share - Additional Information (Detail) (Stock Options [Member])	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share attributable to common stockholders	1,548,014	942,165

LongTerm_Debt_Additional_Infor

Long-Term Debt - Additional Information (Detail) (Mid Cap [Member], Secured Debt [Member], USD $)	3 Months Ended
	Mar. 31, 2015	Jan. 03, 2013
Debt Instrument [Line Items]
Term loan, borrowings		$5,000,000
Interest on term loan		8.00%
Term loan, Interest payment period	45 months
Term loan, payment description	15-month interest-only period, the term loan principal balance, along with any accrued interest, is to be paid in 30 equal monthly installments
Term loan, first periodic payment date	1-Apr-14
Term loan, last periodic payment date	1-Sep-16
Final principal payments made to lender	175,000
Debt instrument principal payment	3,236,019
Debt instrument prepayment fee	$30,000
Interest-Only-Strip [Member]
Debt Instrument [Line Items]
Term loan, Interest payment period	15 months
Principal-Only-Strip [Member]
Debt Instrument [Line Items]
Term loan, Interest payment period	30 months