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Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Taxes

Schedule of reconciliation of U.S. statutory income tax rate to effective tax rate

		Year Ended December 31,
		2017			2016			2015
Federal income tax (benefit) at statutory rate			34.00	%		34.00	%		34.00	%
Permanent differences			(1.16	)		(0.85	)		(0.86	)
Federal research and development credits and adjustments			2.36			2.43			2.64
State income tax, net of federal benefit			5.80			5.70			5.77
Tax reform deferred rate change			(72.21	)		—			—
Other			(0.36	)		(0.40	)		0.28
Change in valuation allowance			31.57			(40.88	)		(41.82	)
​	​	​	​	​	​	​	​	​	​	​
Effective income tax rate			—	%		—	%		—	%
​	​	​	​	​	​	​	​	​	​	​
​	​	​	​	​	​	​	​	​	​	​

Schedule of components of deferred tax assets

        The Company's deferred tax assets consisted of the following (in thousands):

		Year Ended December 31,
		2017			2016
Deferred tax assets
Net operating loss carryforwards		$	41,436		$	48,682
Tax credit carryforwards			5,896			4,833
Capitalized research and development			1,879			3,394
Capitalized legal expenses			1,156			1,597
Other differences			1,048			1,335
​	​	​	​	​	​	​	​
Total deferred tax assets			51,415			59,841
Valuation allowance			(51,415	)		(59,841	)
​	​	​	​	​	​	​	​
Net deferred tax assets		$	—		$	—
​	​	​	​	​	​	​	​
​	​	​	​	​	​	​	​

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- References

No definition available.

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- Definition

Tabular disclosure of the components of net deferred tax asset or liability recognized in an entity's statement of financial position, including the following: the total of all deferred tax liabilities, the total of all deferred tax assets, the total valuation allowance recognized for deferred tax assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319

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- Definition

Tabular disclosure of the reconciliation using percentage or dollar amounts of the reported amount of income tax expense attributable to continuing operations for the year to the amount of income tax expense that would result from applying domestic federal statutory tax rates to pretax income from continuing operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319

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