Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

Schedule of Reconciliation of U.S Federal Statutory Income Tax Rate to Company's Effective Income Tax Rate

A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:

	Year Ended December 31,
	2016			2015			2014
Federal statutory income tax rate		(34.0	)%		(34.0	)%		(34.0	)%
Research and development tax credits		(8.8	)		(5.7	)		(3.8	)
State taxes, net of federal benefit		(5.8	)		(5.3	)		(5.3	)
Stock-based compensation		(6.3	)		4.1			2.3
Revaluation of preferred stock warrant liability		—			—			3.3
Other		0.1			0.3			0.2
Change in deferred tax asset valuation allowance		54.8			40.6			37.3
Effective income tax rate		—	%		—	%		—	%

Schedule of Net Deferred Tax Assets

Net deferred tax assets as of December 31, 2016 and 2015 consisted of the following:

	December 31,
	2016			2015
Deferred tax assets:
Net operating loss carryforwards	$	18,481		$	25,293
Research and development tax credit carryforwards		14,991			4,180
Capitalized organization costs		483			527
Stock-based compensation expense		5,624			1,897
Charitable Contributions		6			5
Deferred Revenue		42,742			—
Accrued expenses		5,560			977
Capitalized research and development expenses		115			126
Total deferred tax assets	$	88,002			33,005
Deferred tax liabilities:
Depreciation and amortization		(5,008	)		(228	)
Total deferred tax liabilities		(5,008	)		(228	)
Valuation allowance	$	(82,994	)		(32,777	)
Net deferred tax assets	$	—		$	—

Summary of Changes In Valuation Allowance for Deferred Tax Assets

Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2016, 2015 and 2014 related primarily to the increases in net operating loss carryforwards, research and development tax credit carryforwards and stock-based compensation were as follows:

	Year Ended December 31,
	2016			2015			2014
Valuation allowance at beginning of year	$	(32,777	)	$	(10,522	)	$	(4,294	)
Decreases recorded as benefit to income tax provision		—			—			—
Increases recorded to income tax provision		(50,217	)		(22,255	)		(6,228	)
Valuation allowance as of end of year	$	(82,994	)	$	(32,777	)	$	(10,522	)