Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2015

Stock-Based Compensation

Summary of Company's grant date fair value and assumptions used in determining fair value of stock options

	Three Months Ended March 31,
	2015	2014
Volatility	79%-82%	84%-86%
Risk-free interest rate	1.31%-1.57%	1.46%-1.76%
Dividend yield	0.0%	0.0%
Expected option term (in years)	6.25	6.25
Weighted-average fair value of stock options granted	$11.66	$14.35

Summary of Company's stock option activity

	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life in Years	Aggregate Intrinsic Value (in thousands)
Options outstanding at December 31, 2014	4,400,106		$	10.59
Granted	619,150		$	16.83
Exercised	(178,071	)	$	8.28
Forfeited or expired	(19,750	)	$	14.49
Options outstanding at March 31, 2015	4,821,435		$	11.46	8.19	$	45,030
Vested and expected to vest at March 31, 2015	4,593,714		$	11.33	8.17	$	43,494
Exercisable at March 31, 2015	1,552,681		$	8.25	7.72	$	19,496

Summary of range of exercise prices and the number of stock options outstanding and exercisable

Outstanding as of March 31, 2015					Exercisable as of March 31, 2015
			Weighted
			Average
			Remaining	Weighted
Range of Exercise		Number of	Contractual	Average	Number of	Weighted Average
Prices		Options	Term (in years)	Exercise Price	Options	Exercise Price
3.03	3.29	180,188	6.75	3.05	131,810	3.04
3.40	3.40	708,314	7.45	3.40	442,697	3.40
3.60	6.90	605,545	7.70	6.02	327,413	5.91
6.96	12.44	885,025	7.65	11.05	358,377	11.09
12.58	12.58	577,550	8.39	12.58	25,000	12.58
12.66	14.65	483,800	8.77	13.91	84,000	14.13
14.81	16.07	583,650	9.38	15.96	28,175	15.62
16.19	20.49	779,363	8.77	19.49	151,458	19.59
21.09	21.21	3,000	9.97	21.17	—	—
21.54	21.54	15,000	8.81	21.54	3,751	21.54

Summary of Company's RSU activity

			Weighted
	Number of		Average
	RSUs		Grant Price
Outstanding at December 31, 2014	20,502		$	19.47
Granted	49,776		16.07
Released	(17,568	)	20.49
Outstanding at March 31, 2015	52,710		$	15.92
Expected to vest	52,710		$	15.92

Summary of aggregate stock-based compensation recorded in the Consolidated Statements of Comprehensive Loss

	Three months ended March 31,
	2015		2014
	(in millions)
Research and development expenses	$	1.3	$	0.9
General and administrative expenses	3.2		1.5
Total	$	4.5	$	2.4