Stock-Based Compensation (Details 2) (USD $)	12 Months Ended	0 Months Ended				1 Months Ended	12 Months Ended		0 Months Ended	3 Months Ended								0 Months Ended
	Dec. 31, 2014	Dec. 09, 2014	Dec. 05, 2012	Mar. 20, 2013	Dec. 05, 2012	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014
Aggregate intrinsic value
Development stage product development revenues	$ 0									0								$ 0
Additional disclosures
Total unrecognized compensation cost, net of estimated forfeitures, related to unvested stock options and restricted stock units (in dollars)	27,300,000									27,300,000								27,300,000
Weighted average period for recognition of compensation cost related to unvested stock awards	2 years 10 months 24 days
Service based restricted stock units | 2012 Plan
Additional disclosures
Total unrecognized compensation cost, net of estimated forfeitures, related to unvested stock options and restricted stock units (in dollars)	1,000,000									1,000,000								1,000,000
Weighted average period for recognition of compensation cost related to unvested stock awards	2 years
Service based restricted stock units | CEO
Shares
Granted (in shares)		30,902	128,205
Additional disclosures
Granted (in dollars per share)	$ 8.75	$ 32.36	$ 7.80
Performance based restricted stock units
Additional disclosures
Share-based compensation expense	0
Performance based restricted stock units | CEO
Shares
Granted (in shares)		23,176	64,103			32,051
Vested (in shares)						(19,230)
Additional disclosures
Granted (in dollars per share)				$ 10.00	$ 8.75
Founder
Shares
Unvested at the beginning of the period (in shares)	987,081						1,645,141						987,081				1,645,141
Vested (in shares)	(658,060)						(658,060)
Unvested at the end of the period (in shares)	329,021					987,081	987,081	1,645,141	987,081	329,021				987,081				329,021
Additional disclosures
Share-based compensation expense	7,500,000						1,400,000	800,000
Stock options
Shares
Outstanding at the beginning of the period (in shares)	2,413,237												2,413,237
Granted (in shares)	2,464,138
Exercised (in shares)	(370,808)
Forfeited (in shares)	(852,564)
Cancelled (in shares)	(25,375)
Outstanding at the end of the period (in shares)	3,628,628					2,413,237	2,413,237		2,413,237	3,628,628				2,413,237				3,628,628
Exercisable at the end of the period (in shares)	688,562									688,562								688,562
Vested and expected to vest at the end of the period (in shares)	2,394,044									2,394,044								2,394,044
Weighted average exercise price per share
Outstanding at the beginning of the period (in dollars per share)	$ 9.26												9.26
Granted (in dollars per share)	$ 19.12
Exercised (in dollars per share)	$ 3.81
Forfeited (in dollars per share)	$ 11.51
Cancelled (in dollars per share)	$ 5.48
Outstanding at the end of period (in dollars per share)	$ 16.01					9.26	$ 9.26		$ 9.26	16.01				9.26				$ 16.01
Exercisable at the end of the period (in dollars per share)	$ 8.43									8.43								$ 8.43
Vested and expected to vest at the end of the period (in dollars per share)	$ 15.11									15.11								$ 15.11
Weighted average remaining contractual term
Outstanding at the beginning of the period	9 years 1 month 10 days								9 years 18 days
Outstanding at the end of the period	9 years 1 month 10 days								9 years 18 days
Exercisable at the end of the period	8 years 26 days
Vested and expected to vest at the end of the period	9 years 4 days
Aggregate intrinsic value
Outstanding at the beginning of the period	6,087,000												6,087,000
Outstanding at the end of period	102,355,000					6,087,000	6,087,000		6,087,000	102,355,000				6,087,000				102,355,000
Exercisable at the end of period	24,641,000									24,641,000								24,641,000
Vested and expected to vest at the end of the period	69,692,000									69,692,000								69,692,000
Total intrinsic value	4,200,000						400,000	48,000
Stock options | Minimum
Assumptions used to estimate fair value of each stock-based option award on the grant date using the Black-Scholes option pricing model
Risk free interest rate (as a percent)	1.62%						0.91%	0.80%
Volatility (as a percent)	76.00%						83.00%	79.00%
Expected term	5 years 3 months 18 days						5 years 1 month 6 days	5 years 1 month 6 days
Stock options | Maximum
Assumptions used to estimate fair value of each stock-based option award on the grant date using the Black-Scholes option pricing model
Risk free interest rate (as a percent)	2.17%						2.11%	1.78%
Volatility (as a percent)	84.00%						91.00%	89.00%
Expected term	9 years 11 months 19 days						9 years 11 months 5 days	9 years 11 months 5 days
Stock options | Employees
Shares
Granted (in shares)	2,434,138						1,537,172
Weighted average exercise price per share
Granted (in dollars per share)	$ 19.19						$ 12.87
Additional disclosures
Weighted average grant-date fair value of options granted (in dollars per share)	$ 13.41						$ 9.34
Share-based compensation expense	3,300,000						2,300,000	300,000
Stock options | Non-employees
Shares
Granted (in shares)	30,000						0
Weighted average exercise price per share
Granted (in dollars per share)	$ 13.26
Additional disclosures
Share-based compensation expense	8,300,000						2,200,000	1,000,000
Restricted stock units
Additional disclosures
Vested in period fair value							800,000
Share-based compensation expense	800,000						700,000	36,000
Restricted stock units | CEO
Shares
Granted (in shares)		54,078	192,308
Vested (in shares)										16,025	16,025	16,025	16,025	16,025	16,025	16,025	16,025
Restricted stock units | CEO | Vesting on March 31, 2015
Shares
Vested (in shares)		3,863
Restricted stock units | CEO | Vesting quarterly until December 31, 2016
Shares
Vested (in shares)		3,863
Restricted stock units | Service based restricted stock units
Additional disclosures
Share-based compensation expense																		$ 30,000