Income Taxes Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Deferred Tax Assets and Liabilities

The following table represents the significant components of the Company’s deferred tax assets and liabilities for the periods presented:

	December 31,
	2016			2017
Deferred tax assets:
Net operating loss carryforwards	$	31,618		$	21,627
Credit carryforwards	3,200			4,230
Stock-based compensation	1,801			2,806
Accruals and reserves	4,588			3,953
Gross deferred tax assets	41,207			32,616
Valuation allowance	(38,307		)	(29,818		)
Total deferred tax assets, net of valuation allowance	2,900			2,798
Deferred tax liabilities:
Intangible assets	(1,419		)	(847		)
Prepaid expenses	(1,481		)	(1,951		)
Total deferred tax liabilities	(2,900		)	(2,798		)
Net deferred tax assets and liabilities	$	—		$	—

Summary of Operating Loss Carryforwards

The following table represents the Company’s NOL carryforwards as of December 31, 2016 and 2017:

	December 31,
	2016	2017
Federal	84,973	87,071
Various states	4,133	4,231

Schedule of Effective Income Tax Rate Reconciliation

The reconciliation of the U.S. federal income tax at statutory rate with the Company’s effective income tax rate:

	December 31,
	2015		2016		2017
U.S. federal income tax at statutory rate	34.00	%	34.00	%	34.00	%
State taxes (net of federal benefit)	3.86		2.49		2.40
Permanent differences	(2.94	)	(8.21	)	(15.03	)
Federal research and development credit	2.42		2.06		7.08
Change in valuation allowance	(37.36	)	(30.19	)	(27.79	)
Nondeductible expenses and others	0.02		(0.15	)	(0.66	)
Change in valuation allowance for Tax Act impact	—		—		84.37
Change in deferred balance before valuation allowance for Tax Reform impact	—		—		(84.37	)
Effective income tax rate	—	%	—	%	—	%

Schedule of Unrecognized Tax Benefits Roll Forward

The following table summarized the activity related to unrecognized tax benefits:

	December 31,
	2016		2017
Unrecognized benefit—beginning of year	$	684	$	800
Gross increases (decreases)—prior year tax positions	—		(7		)
Gross increases (decreases)—current year tax positions	116		264
Unrecognized benefit—end of year	$	800	$	1,057