INCOME TAXES (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Domestic and Foreign Components of Loss before Income Taxes

The domestic and foreign components of loss before income taxes are as follows, in thousands:

	2017			2016			2015
Domestic	$	(378,293	)	$	(350,704	)	$	(245,681	)
Foreign		(112,581	)		(59,404	)		(44,392	)
Loss before income taxes	$	(490,874	)	$	(410,108	)	$	(290,073	)

Schedule of Components of Net Deferred Tax (Liability) Asset

Components of the net deferred tax (liability) asset at December 31, 2017 and 2016 are as follows, in thousands:

	2017			2016
Deferred tax assets:
Net operating loss carryforwards	$	405,784		$	346,965
Research and development credits		192,094			111,394
AMT credits		788			788
Foreign tax credits		—			3,196
Capitalized research and development and start-up costs		13,163			18,138
Deferred revenue		13,576			20,853
Deferred compensation		42,990			51,355
Intangible assets		9,018			14,725
Partnership interest		—			1,623
Other		11,608			7,845
Total deferred tax assets		689,021			576,882
Deferred tax liabilities:
Unrealized gain on available-for-sale securities		(765	)		(1,524	)
Deferred tax asset valuation allowance		(688,256	)		(575,358	)
Net deferred tax liability	$	—		$	—

Schedule of Effective Income Tax Rate Differs from Statutory Federal Income Tax Rate

Our effective income tax rate differs from the statutory federal income tax rate as follows for the years ended December 31, 2017, 2016 and 2015:

	2017			2016			2015
At U.S. federal statutory rate		35.0	%		35.0	%		35.0	%
State taxes, net of federal effect		3.8			3.7			4.0
Stock-based compensation		3.3			(1.4	)		(1.1	)
Tax credits		9.9			11.8			8.0
Orphan drug credit		(3.4	)		(3.5	)		(2.0	)
Other permanent items		(1.0	)		(0.4	)		(0.1	)
Foreign rate differential		(8.1	)		(5.1	)		(5.4	)
Tax reform change		(46.5	)		—			—
Other		(0.9	)		—			—
Valuation allowance		7.9			(40.1	)		(38.4	)
Effective income tax rate		—	%		—	%		—	%