Income taxes (Tables)

12 Months Ended

Dec. 31, 2015

Provision for Income Taxes

The provision for income taxes consists of the following (in thousands):

	Year Ended December 31,
	2015			2014			2013
Current
U.S. federal	$	—		$	—		$	—
U.S. state		—			—			—
Non-U.S.		—			—			—
Total current		—			—			—
Deferred
U.S. federal		109,512			57,873			59,379
U.S. state		(29,394	)		7,631			7,470
Non-U.S.		—			—			—
Valuation Allowance		(80,118	)		(65,504	)		(66,849	)
Total deferred		—			—			—
Total	$	—		$	—		$	—

Components of Net Deferred Tax Asset

Components of the net deferred tax asset as of December 31, 2015 and 2014 are approximately as follows (in thousands):

	December 31,
	2015			2014
Deferred tax assets:
Net operating loss carryforwards	$	721,588		$	699,997
Research and development credits		73,646			73,227
Capitalized research		5,872			28,516
Payments from collaboration		52,484			19,217
Milestone Rights		3,242			5,321
Accrued expenses		251			768
Loss on purchase commitment		24,084			—
Non-qualified stock option expense		16,941			43,691
Capitalized patent costs		8,574			8,624
Other		7,186			131
Depreciation		48,755			3,010
Total net deferred tax assets		962,623			882,502
Valuation allowance		(962,623	)		(882,502	)
Net deferred tax assets	$	—		$	—

Effective Income Tax Rate

The Company’s effective income tax rate differs from the statutory federal income tax rate as follows for the years ended December 31, 2015, 2014 and 2013:

	December 31,
	2015			2014			2013
Federal tax benefit rate		35.0	%		35.0	%		35.0	%
State tax benefit, net of federal benefit		—			—			—
Permanent items		—			0.9			—
Intercompany transfer of intellectual property		(1.0	)		(4.1	)		(4.3	)
Valuation allowance		(34	)		(31.8	)		(30.7	)
Effective income tax rate		0.0	%		0.0	%		0.0	%