Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

Income Taxes

Schedule of reconciliation of the U.S. federal statutory rate to the Company?s effective tax rate

	Year Ended December 31,
	2016		2015		2014
Tax at statutory rates	35.0	%	35.0	%	35.0	%
State income taxes	5.2		6.6		5.1
Permanent differences	(1.2)		(1.3)		(0.8)
Research and development credits	1.3		1.5		1.9
Change in valuation allowance	(40.3)		(41.8)		(41.2)
Effective tax rate	0.0	%	0.0	%	0.0	%

Schedule of Deferred Tax Assets

The significant components of the Company’s deferred tax asset consist of the following at December 31, 2016 and 2015 (in thousands):

	December 31,
	2016		2015
Deferred tax assets:
Net operating loss carryforwards	$	69,411	$	49,417
Tax credits		5,269		4,107
Other temporary differences		1,636		1,623
Start-up expenditures		5,088		5,288
Stock option expenses		2,779		1,649
Total deferred tax assets		84,183		62,084
Deferred tax asset valuation allowance		(83,924)		(61,813)
Net deferred tax assets		259		271
Deferred tax liabilities:
Prepaid expenses		(259)		(271)
Net deferred taxes	$	—	$	—