Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

Income Tax Disclosure [Abstract]

Schedule of Components of Income Tax Expense (Benefit)

The following table summarizes the components of our income tax (benefit) expense (in thousands):

	Year ended December 31,
	2016			2015			2014
Current:
Federal	$	—		$	—		$	—
State	1			1			1
	1			1			1
Deferred:
Federal	(5		)	(17		)	—
State	—			(2		)	—
	(5		)	(19		)	—
Income tax (benefit) expense	$	(4	)	$	(18	)	$	1

Schedule of Effective Income Tax Rate Reconciliation

The following is a reconciliation of the expected statutory federal income tax provision to our actual income tax provision (in thousands):

	Year ended December 31,
	2016			2015			2014
Expected income tax benefit at federal statutory tax rate	$	(27,826	)	$	(18,960	)	$	(19,271	)
State income taxes, net of federal benefit	(1,152		)	(1,580		)	(2,348		)
Tax credits	(5,447		)	(5,039		)	(3,307		)
Change in fair value of convertible note payable	—			616			4,120
Change in valuation allowance	31,990			23,216			20,047
Prior year true-up	(1,320		)	110			(92		)
Stock compensation	2,458			1,161			902
Reserve for uncertain tax positions	1,314			254			—
Other	(21		)	204			(50		)
Income tax (benefit) expense	$	(4	)	$	(18	)	$	1

Schedule of Deferred Tax Assets and Liabilities

The following table summarizes the significant components of our deferred tax assets and liabilities (in thousands):

	December 31,
	2016			2015
Deferred tax assets:
Net operating loss carryovers	$	70,739		$	48,912
Research and development and other tax credits	22,613			15,148
Deferred revenue	735			1,210
Intangibles and property and equipment basis difference	—			2,097
Stock compensation expense	5,664			3,488
Other	4,679			1,129
Total deferred tax assets	104,430			71,984
Total deferred tax liabilities	(799		)	(343		)
Net deferred tax asset	103,631			71,641
Valuation allowance	(103,631		)	(71,641		)
Net deferred tax asset	$	—		$	—

Summary of Income Tax Contingencies

The following table summarizes the changes in the amount of our unrecognized tax benefits (in thousands):

	Year Ended December 31,
	2016		2015			2014
Beginning balance of unrecognized tax benefits	$	2,298	$	1,853		$	1,092
Increase (decrease) for prior year tax positions	1,991		(250		)	(73		)
Increase for current year tax positions	1,343		695			834
Total	$	5,632	$	2,298		$	1,853