Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Schedule of Domestic and Foreign Components of Loss before Income Taxes

The domestic and foreign components of loss before income taxes were as follows (in thousands):

	Year Ended December 31,
	2017			2016			2015
Domestic	$	(38,706	)	$	(27,148	)	$	(12,832	)
Foreign	$	(1,180	)		(5,493	)		(321	)
Loss before income taxes	$	(39,886	)	$	(32,641	)	$	(13,153	)

Reconciliation of U.S. Federal Statutory Income Tax Rate to Company's Effective Income Tax Rate

A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:

	Year Ended December 31,
	2017			2016			2015
Federal statutory income tax rate		(34.0	)		(34.0	)		(34.0	)
Federal and state research and development tax credit		(3.3	)		(1.7	)		(0.9	)
State taxes, net of federal benefit		(5.3	)		(4.4	)		(5.2	)
Foreign rate differential		0.1			2.3			0.3
Nondeductible items		(0.1	)		4.8			10.2
Effect of US tax reform		23.8			—			—
Increase in deferred tax asset valuation allowance		18.8			33.0			29.6
Effective income tax rate		—			—			—

Net Deferred Tax Assets

Net deferred tax assets as of December 31, 2017 and 2016 consisted of the following (in thousands):

	December 31,
	2017			2016
Net operating loss carryforwards	$	21,754		$	16,406
Research and development tax credit carryforwards		2,022			697
Other		743			49
Total deferred tax assets		24,519			17,152
Valuation allowance		(24,519	)		(17,152	)
Net deferred tax assets	$	—		$	—

Summary of Changes in Valuation Allowance for Deferred Tax Assets

Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2017 and 2016 related primarily to the increase in net operating loss carryforwards, capitalized research and development expenses and research and development tax credit carryforwards and were as follows (in thousands):

	December 31,
	2017			2016
Valuation allowance as of beginning of year	$	(17,152	)	$	(6,157	)
Decreases recorded as benefit to income tax provision		—			—
Increases recorded to income tax provision		(7,367	)		(10,995	)
Valuation allowance as of end of year	$	(24,519	)	$	(17,152	)