Stock Based Compensation- Schedule of Stock Options Outstanding (Detail) - $ / shares	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding, total shares	6,680,011	5,338,707
Outstanding, weighted-average remaining contractual life	9 years	9 years 2 months 12 days
Outstanding, weighted-average exercise price	$ 21.15	$ 14.01
Exercisable, total shares	1,628,142
Exercisable, weighted-average exercise price	$ 3.81
Exercise Price 0.38
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding, total shares	346,542
Outstanding, weighted-average remaining contractual life	6 years 7 months 6 days
Outstanding, weighted-average exercise price	$ 0.38
Exercisable, total shares	281,542
Exercisable, weighted-average exercise price	$ 0.38
Exercise Price 0.70
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding, total shares	956,543
Outstanding, weighted-average remaining contractual life	8 years 4 months 24 days
Outstanding, weighted-average exercise price	$ 0.70
Exercisable, total shares	617,688
Exercisable, weighted-average exercise price	$ 0.70
Exercise Price 1.35
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding, total shares	1,180,377
Outstanding, weighted-average remaining contractual life	8 years 8 months 12 days
Outstanding, weighted-average exercise price	$ 1.35
Exercisable, total shares	410,886
Exercisable, weighted-average exercise price	$ 1.35
Exercise Price 6.89
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding, total shares	837,092
Outstanding, weighted-average remaining contractual life	8 years 10 months 24 days
Outstanding, weighted-average exercise price	$ 6.89
Exercisable, total shares	182,117
Exercisable, weighted-average exercise price	$ 6.89
Exercise Price 17.00 - 32.56
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit	17.00
Exercise price range, upper limit	$ 32.56
Outstanding, total shares	868,157
Outstanding, weighted-average remaining contractual life	9 years 2 months 12 days
Outstanding, weighted-average exercise price	$ 26.06
Exercisable, total shares	94,659
Exercisable, weighted-average exercise price	$ 17.00
Exercise Price 40.30 - 51.96
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit	40.30
Exercise price range, upper limit	$ 51.96
Outstanding, total shares	779,300
Outstanding, weighted-average remaining contractual life	9 years 4 months 24 days
Outstanding, weighted-average exercise price	$ 50.16
Exercisable, total shares	30,000
Exercisable, weighted-average exercise price	$ 51.43
Exercise Price 53.90 - 59.23
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit	53.90
Exercise price range, upper limit	$ 59.23
Outstanding, total shares	730,000
Outstanding, weighted-average remaining contractual life	9 years 7 months 6 days
Outstanding, weighted-average exercise price	$ 54.89
Exercisable, total shares	1,875
Exercisable, weighted-average exercise price	$ 54.47
Exercise Price 60.61 - 65.50
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower limit	60.61
Exercise price range, upper limit	$ 65.50
Outstanding, total shares	847,000
Outstanding, weighted-average remaining contractual life	9 years 8 months 12 days
Outstanding, weighted-average exercise price	$ 63.97
Exercisable, total shares	9,375
Exercisable, weighted-average exercise price	$ 63.52
Exercise Price 71.45
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding, total shares	125,000
Outstanding, weighted-average remaining contractual life	9 years 6 months
Outstanding, weighted-average exercise price	$ 71.45
Exercise Price 72.42
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Outstanding, total shares	10,000
Outstanding, weighted-average remaining contractual life	9 years 7 months 6 days
Outstanding, weighted-average exercise price	$ 72.42