Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Significant components deferred tax assets

eferred tax assets are as follows (in thousands):



	December 31,
	2019			2018
Deferred tax assets:
Net operating loss carryforwards	$	81,406		$	60,105
Research and development credits	24,011			21,262
Deferred royalty obligation	30,460			31,937
Share-based compensation expense	9,581			11,904
Depreciation and amortization expense	—			1,033
Lease liability	7,127			—
Other	1,263			1,004
Total gross deferred tax assets	153,848			127,245
Deferred tax liabilities:
Depreciation and amortization	(1,612		)	—
Right-of-use lease asset	(3,775		)	—
Valuation allowance	(148,461		)	(127,245		)
Net deferred tax assets	$	—		$	—

Provision for income taxes

The difference between income taxes computed using the U.S. federal income effective tax rate and the provision for income taxes is as follows (in thousands):



	Year Ended December 31,
	2019			2018
Federal statutory rate	$	(24,467	)	$	(41,888	)
State tax benefit	(3,825		)	(14,449		)
Change in valuation allowance	102,583			55,167
Share-based compensation expense	7,532			4,041
State rate true-up	2,513			—
Section 382 limited tax attributes/expired	—			1,936
Establishment of NOLs and credits, post-Section 382 ownership change	(81,368		)	—
Research and development credits	(2,599		)	(5,164		)
Foreign rate differential	(62		)	(58		)
Other permanent differences	(307		)	415
Provision for income taxes	$	—		$	—