Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

The following is a reconciliation of the statutory federal income tax rate to the Company’s effective tax rate:


	December 31,
	2016			2015			2014
Expected income tax provision at the federal statutory rate		35.0	%		35.0	%		35.0	%
State taxes, net of federal benefit		0.3			(3.8	)		4.6
Change in valuation allowance		(36.2	)		(30.7	)		(17.9	)
Nondeductible expenses		—			—			(20.6	)
Tax credits		0.3			1.3			—
Other		0.6			(1.7	)		(3.2	)

Income tax provision		0.0	%		0.1	%		(2.1	%)

Significant components of the Company’s deferred tax assets are as follows:


	December 31,
	2016			2015
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	68,639		$	30,572
Research credits		2,643			1,919
Stock awards		2,583			1,011
Other		1,558			571

Gross deferred tax assets		75,423			34,073
Valuation allowance		(74,520	)		(33,845	)

Total deferred tax assets		903			228
Deferred tax liabilities		(903	)		(228	)

Net deferred tax assets	$	—		$	—

A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows:


	December 31,
	2016		2015			2014
	(in thousands)
Balance at beginning of year	$	3,298	$	2,815		$	1,411
Additions (subtractions) based on tax positions related to prior year		45		(58	)		405
Additions based on tax positions related to current year		549		541			999

Balance at end of year	$	3,892	$	3,298		$	2,815