Stock award plans (Tables)

12 Months Ended

Dec. 31, 2015

Stock Based Award Plans

The following table summarizes information about the Company’s stock-based award plans as of December 31, 2015:

	Outstanding Options		Outstanding Restricted Stock Units		Shares Available for Future Issuance
2004 Equity Incentive Plan		11,309,136		276,784		—
2013 Equity Incentive Plan		8,026,762		1,527,836		15,540,652
2004 Non-Employee Directors’ Stock Option Plan		443,331		—		—
Total		19,779,229		1,804,620		15,540,652

Stock Based Compensation Expense Recognized in Accompanying Statements of Operations

Total stock-based compensation expense recognized in the accompanying statements of operations is as follows (in thousands):

	Year Ended December 31,
	2015		2014		2013
Employee-related	$	8,407	$	48,622	$	45,181
Consultant-related		318		—		5
Total	$	8,725	$	48,622	$	45,186

Stock Based Compensation Expense Recognized in Accompanying Statements of Operations by Category

Total stock-based compensation expense recognized in the accompanying statements of operations is included in the following categories (in thousands):

	Year Ended December 31,
	2015		2014		2013
Research and development	$	3,029	$	22,357	$	20,409
General and administrative		5,696		26,265		24,777
Total	$	8,725	$	48,622	$	45,186

Assumptions Used to Calculate Fair Value of Employee Stock Options

The Company calculated the fair value of employee stock options granted during the years ended December 31, 2015, 2014 and 2013 using the following assumptions:

	Year Ended December 31,
	2015		2014		2013
Risk-free interest rate		1.61% — 1.86%		1.64% — 2.11%		0.94% — 1.82%
Expected lives		5.79 — 5.86 years		5.77 — 6.09 years		2.64 — 5.77 years
Volatility		69.76% — 71.84%		73.98% — 84.85%		75.83% — 86.26%
Dividends		—		—		—

Summary of Stock Options Outstanding

The following table summarizes information about stock options outstanding:

	Number of Shares			Weighted Average Exercise Price per Share		Aggregate Intrinsic Value ($000)
Outstanding at January 1, 2015		21,541,664			4.53	$	33,495
Granted		1,541,100			4.11
Exercised		(1,700,964	)		1.91
Forfeited		(706,387	)		5.78
Expired		(896,184	)		7.70
Outstanding at December 31, 2015		19,779,229			4.54	$	—
Vested and expected to vest at December 31, 2015		19,597,097			4.53	$	—
Exercisable at December 31, 2015		17,217,332			4.47	$	—

Summary of Restricted Stock Unit Activity

A summary of restricted stock unit activity for the year ended December 31, 2015 is presented below:

	Number of Shares			Weighted Average Grant Date Fair Value per Share
Outstanding at January 1, 2015		2,610,720		$	5.20
Granted		1,133,404		$	4.14
Vested		(1,111,134	)	$	4.93
Forfeited		(828,370	)	$	4.88
Outstanding at December 31, 2015		1,804,620		$	4.85