Income Taxes (Tables)

12 Months Ended

Dec. 31, 2015

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,
	2015			2014		2013
Current:
Federal	$	—		$	—	$	—
State	1			1		1
	1			1		1
Deferred:
Federal	(17		)	—		(20		)
State	(2		)	—		(4		)
	(19		)	—		(24		)
Income tax (benefit) expense	$	(18	)	$	1	$	(23	)

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,
	2015			2014			2013
Expected income tax benefit at federal statutory tax rate	$	(18,960	)	$	(19,271	)	$	(6,355	)
State income taxes, net of federal benefit	(1,580		)	(2,348		)	(1,090		)
Tax credits	(5,039		)	(3,307		)	(2,406		)
Change in fair value of convertible note payable	616			4,120			456
Change in valuation allowance	23,216			20,047			9,026
Prior year true-up	110			(92		)	(235		)
Stock compensation	1,161			902			667
Reserve for uncertain tax positions	254			—			—
Other	204			(50		)	(86		)
Income tax (benefit) expense	$	(18	)	$	1		$	(23	)

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,
	2015			2014
Deferred tax assets:
Net operating loss carryovers	$	48,912		$	34,954
Research and development and other tax credits	15,148			8,732
Deferred revenue	1,210			1,919
Intangibles and property and equipment basis difference	2,097			1,874
Stock compensation expense	3,488			1,999
Other	1,129			617
Total deferred tax assets	71,984			50,095
Total deferred tax liabilities	(343		)	(1,670		)
Net deferred tax asset	71,641			48,425
Valuation allowance	(71,641		)	(48,425		)
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,
	2015			2014			2013
Beginning balance of unrecognized tax benefits	$	1,853		$	1,092		$	569
(Decrease) increase for prior year tax positions	(250		)	(73		)	137
Increase for current year tax positions	695			834			386
Total	$	2,298		$	1,853		$	1,092