INCOME TAXES (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Schedule of Deferred Tax Assets and Liabilities

(in thousands)	2018			2017
Deferred tax assets (liabilities):
Net operating loss carryforwards	$	122,678		$	83,656
Research and development credits		15,217			10,491
Noncash compensation		4,394			4,934
Other		658			632
Deferred tax assets, excluding valuation allowance		142,947			99,713
Less valuation allowance		(142,947	)		(99,713	)
Net deferred tax assets	$	--		$	--

Schedule of Effective Income Tax Rate Reconciliation

	For the year ended December 31,
(in thousands)	2018			2017			2016
Loss before income taxes, as reported in the consolidated statements of operations	$	(173,482	)	$	(118,476	)	$	(78,253	)
Computed “expected” tax benefit	$	(36,431	)	$	(40,282	)	$	(26,606	)
Increase (decrease) in income taxes resulting from:
Expected benefit from state and local taxes		(2,243	)		(1,106	)		(835	)
Research and development credits		(4,726	)		(3,697	)		(2,364	)
Other		639			1,563			(8	)
Stock awards		(473	)		8,213			--
Enactment of federal tax reform		--			51,768			--
Change in the balance of the valuation allowance for deferred tax assets		43,234			(16,459	)		29,813
	$	--		$	--		$	--