Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock-Based Compensation Expense for Options Granted and Restricted Stock as Reflected in the Statement of Operations

Stock-based compensation expense for options granted, RSAs, and stock purchase rights are reflected in the statement of operations as follows:

	YEAR ENDED DECEMBER 31,
(in thousands)	2015		2014		2013
Research and development	$	2,500	$	1,339	$	222
General and administrative	10,445		7,839		2,636
Total	$	12,945	$	9,178	$	2,858

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions

Key weighted average assumptions utilized in the fair value calculation for the underlying common stock as of December 31, 2015, 2014 and 2013 appear on the table below.

	YEAR ENDED DECEMBER 31,
	2015		2014		2013
Expected term (years)	6.07		6.25		6.25
Expected stock price volatility	74.11	%	80.44	%	79.20	%
Risk-free interest rate	1.63	%	1.90	%	1.78	%
Dividend yield	—	%	—	%	—	%

Schedule of Stock Options Activity

The following table summarizes the stock option activity under the Plans:

	NUMBER OF SHARES		WEIGHTED AVERAGE EXERCISE PRICE		WEIGHTED AVERAGE REMAINING CONTRACTUAL LIFE (YEARS)	AGGREGATE INTRINSIC VALUE (000’s)
Options outstanding at December 31, 2014	3,826,459		$	8.39
Granted	1,328,400		24.83
Exercised	(297,763	)	4.38
Canceled	(273,510	)	17.00
Options outstanding at December 31, 2015	4,583,586		$	12.86	8.0	$	55,918
Options vested and expected to vest at December 31, 2015	4,511,052		$	12.75	8.0	$	55,478
Options exercisable at December 31, 2015	2,237,663		$	7.92	7.3	$	37,308

Schedule of Stock Options Outstanding and Exercisable Option Plans

The following table provides additional information about the Company’s stock options that are outstanding and exercisable at December 31, 2015:

EXERCISE PRICE	OPTIONS OUTSTANDING	WEIGHTED AVERAGE REMAINING CONTRACTUAL LIFE (YEARS)	OPTIONS EXERCISABLE
$0.20 - $3.15	2,251,290	7.1	1,606,555
$10.44 - $15.97	148,770	9.6	4,737
$16.21 - $21.08	1,239,250	8.5	477,675
$22.31 - $26.76	336,701	9.2	54,138
$27.44 - $32.30	607,575	9.1	94,558
	4,583,586		2,237,663

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity

The following table summarizes the RSA activity under the Plans:

	NUMBER OF SHARES		WEIGHTED AVERAGE FAIR VALUE PER SHARE
RSAs outstanding at December 31, 2014	103,064		$	2.47
Granted	99,027		28.00
Vested	(69,697	)	3.35
Canceled	(12,401	)	28.74
RSAs outstanding at December 31, 2015	119,993		$	20.31