Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

Income Tax Disclosure [Abstract]

Income Tax Provision (Benefit)

The income tax provision (benefit) consists of the following (in thousands):

	Year Ended December 31,
	2016		2015
Current:
Federal	$	–	$	–
State		–		(365	)
Foreign		–		–
		–		(365	)
Deferred:
Federal	$	–	$	–
State		–		–
Foreign		–		–
		–		–
Total provision (benefit) for income taxes	$	-	$	(365	)

Reconciliation of Effective Tax Rate for the Provision for Income Taxes

The effective tax rate of our provision for income taxes differs from the federal statutory rate as follows:

	Year Ended December 31,
	2016			2015			2014
Federal statutory income tax rate		34.0	%		34.0	%		34.0	%
State income taxes, net of federal benefit		0.0	%		-6.6	%		11.2	%
Federal and state credits		9.5	%		2.5	%		2.7	%
Stock based compensation		-0.1	%		0.0	%		-1.6	%
FIN 48 release		0.0	%		0.2	%		0.0	%
Other		0.1	%		0.0	%		-0.1	%
Change in valuation allowance		-38.6	%		-29.9	%		-46.2	%
Foreign Rate Differential		-4.9	%		0.0	%		0.0	%
Total tax benefit		0.0	%		0.2	%		0.0	%

Components of U.S. Deferred Tax Assets and (Liabilities)

The components of U.S. deferred tax assets and (liabilities) are as follows (in thousands):

	December 31,
	2016			2015
Deferred tax assets:
Federal and state net operating loss carryforwards	$	235,015		$	207,898
Federal and state research tax credit carryforwards		17,927			18,744
Federal Orphan Drug Credit		60,822			–
Deferred revenue		15,566			9,192
Stock options		18,734			10,197
Capitalized acquisition costs		819			974
Other		16,298			3,942
Net deferred tax assets before valuation allowance		365,181			250,947
Valuation allowance		(365,181	)		(250,947	)
Net deferred tax assets	$	–		$	–

Reconciliation of the Beginning and Ending Amount of Unrecognized Tax Benefits

A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands):

	Year Ended December 31,
	2016			2015			2014
Unrecognized tax benefits, beginning of period	$	3,228		$	2,906		$	2,048
Increases due to current period positions		6,919			1,091			858
Decreases due to current period positions		–			–			–
Increase due to prior period positions		4,266			–			–
Decreases due to prior period positions		(548	)		(404	)		–
Decreases due to the lapse of statutes of limitations		–			(365	)		–
Unrecognized tax benefits, end of period	$	13,866		$	3,228		$	2,906