Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Schedule of deferred tax assets and liabilities

Components of the net deferred tax assets at December 31, 2017 and 2016 are as follows, in thousands:



	2017			2016
Deferred tax assets:
Federal and state net operating losses	$	99,252		$	94,793
Research credits	36,819			30,007
Deferred compensation	8,274			9,701
Deferred revenue	9,184			28,096
Accrued expenses	4,977			5,053
Intangibles	2,020			3,220
Depreciation	—			475
Unrealized loss on marketable securities	13			—
Total deferred tax assets	160,539			171,345
Deferred tax liabilities:
Depreciation	(802		)	—
Unrealized gain on marketable securities	—			(30		)
Total deferred tax liabilities	(802		)	(30		)
Valuation allowance	(159,737		)	(171,315		)
Net deferred tax assets	$	—		$	—

Schedule of reconciliation of federal statutory income tax provision to actual provision

A reconciliation of the federal statutory income tax benefit to the Company's actual provision for the years ended December 31, 2017, 2016 and 2015 is as follows (in thousands):



	2017			2016			2015
Benefit at federal statutory tax rate	$	(29,941	)	$	(7,137	)	$	(28,323	)
State taxes, net of federal benefit	(4,713		)	(1,108		)	(4,398		)
Share-based compensation	1,370			5,148			3,634
Tax credits	(2,733		)	(4,120		)	(2,652		)
Other	492			272			42
Change in valuation allowance	(17,817		)	6,945			31,697
Federal statutory rate change	53,342			—			—
Income tax provision	$	—		$	—		$	—

Schedule of reconciliation of unrecognized tax benefits

A reconciliation of the beginning and ending amount of unrecognized tax benefits for the years ended December 31, 2017 and 2016 is as follows (in thousands):



	2017		2016			2015
Balance, beginning of year	$	6,678	$	5,116		$	4,064
Additions for tax positions related to the current year	1,262		1,602			1,395
Reductions of tax positions of prior years	—		(40		)	(343		)
Balance, end of year	$	7,940	$	6,678		$	5,116