Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Taxes [Abstract]

Loss Before Income Taxes

Loss before income taxes is comprised of (in thousands):

	Years Ended December 31,
	2017			2016			2015
	(as revised)
United States	$	(108,691	)	$	(83,217	)	$	(61,422	)
Foreign		(11,593	)		—			—
Loss before income tax expense	$	(120,284	)	$	(83,217	)	$	(61,422	)

Provision for Income Taxes

The provision (benefit) for income taxes is comprised of (in thousands):

	Years Ended December 31,
	2017		2016		2015
Current:
Federal	$	—	$	—	$	—
State		1,041		—		—
Foreign		234		—		—
Total current		1,275		—		—
Deferred:
Federal		—		—		—
State		—		—		—
Foreign		—		—		—
Total deferred		—		—		—
Income tax expense	$	1,275	$	—	$	—

Reconciliation of Statutory to Effective Tax Rate

The reconciliation between our effective tax rate on loss from continuing operations and the statutory U.S. tax rate is as follows (in thousands):

	Years Ended December 31,
	2017					2016					2015
	(as revised)
Pre-tax loss	$	(120,284	)			$	(83,217	)			$	(61,422	)
Statutory rate		(42,099	)	35.0	%		(29,126	)	35.0	%		(21,498	)	35.0	%
State income tax net of federal benefit		(2,371	)	2.0	%		(4,099	)	4.9	%		(3,194	)	5.2	%
Impact of foreign tax rate differential		4,072		(3.4	)%		—		0.0	%		—		0.0	%
Net change in valuation allowance		(18,917	)	15.7	%		43,438		(52.1	)%		30,857		(50.2	)%
Tax credits		4,189		(3.5	)%		(11,007	)	13.2	%		(6,187	)	10.0	%
IPO/Deconsolidation adjustment		37,911		(31.5	)%		—		0.0	%		—		0.0	%
Tax Cut and Jobs Act		19,046		(15.8	)%		—		0.0	%		—		0.0	%
Nondeductible items and other		(556	)	0.5	%		794		(1.0	)%		22		0.0	%
Effective rate	$	1,275		(1.0	)%	$	—		0.0	%	$	—		0.0	%

Deferred Tax Assets and Liabilities

Significant components of our deferred tax assets and liabilities as of December 31, 2017 and 2016 are as follows (in thousands):

	December 31,
	2017			2016
Deferred Tax Assets:	(as revised)
Net operating loss carryovers	$	1,157		$	48,813
Tax credits		29,334			30,057
Stock-based compensation		7,515			6,620
Deferred revenue		29,256			—
Other		240			1,251
Total deferred tax assets		67,502			86,741
Deferred Tax Liabilities:
Intangible assets		(125	)		(281	)
Total deferred tax liabilities		(125	)		(281	)
Valuation allowance		(67,377	)		(86,460	)
Net deferred tax assets and liabilities	$	—		$	—

Gross Unrecognized Tax Benefits

The following table summarizes our gross unrecognized tax benefits (in thousands):

	Years Ended December 31,
	2017			2016		2015
Beginning balance of unrecognized tax benefits	$	5,012		$	1,766	$	138
Additions related to the current year		1,723			3,246		1,628
Decreases related to prior year tax positions		(1,734	)		—		—
Ending balance of unrecognized tax benefits	$	5,001		$	5,012	$	1,766