Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Taxes [Abstract]

Schedule of Deferred Tax Assets and Liabilities

	As of December 31,
	2017			2016
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	186,967		$	258,405
Research and development tax credits	46,682			44,111
Orphan drug credits	26,524			24,233
Capitalized research and development	69,561			86,845
Stock-based compensation	3,923			7,060
Deferred revenue	12,950			39,307
Other	5,579			8,432
Total deferred tax assets	352,186			468,393
Deferred tax liabilities:
Deferred tax liability related to acquisition of Symphony Icon	(10,896		)	(18,675		)
Other	(1		)	—
Total deferred tax liabilities	(10,897		)	(18,675		)
Less: valuation allowance	(347,303		)	(468,393		)
Net deferred tax liabilities	$	(6,014	)	$	(18,675	)