Stock Based Awards - Additional Information (Detail) (USD $)	12 Months Ended			73 Months Ended	1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Feb. 28, 2009
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved	3,900,281	12,078,240		3,900,281
Common stock reserved for future issuance	991,401	9,533	168,571	991,401
Intrinsic value of stock option exercised	$ 800,000	$ 0	$ 0
Unrecognized employee stock-based compensation	20,200,000			20,200,000
Weighted-average remaining vesting period	3 years 1 month 6 days
Additional shares issued	2,531,915	803,590
Voting power per share	One
Recognized compensation expense	4,641,000	215,000	141,000	5,189,000
Weighted Average Remaining Contractual Life, Options outstanding	8 years 9 months 18 days
Employee Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period	4 years
Stock options, weighted-average grant date fair value	$ 16.90	$ 1.60	$ 1.04
Tax benefits realized from options and other share-based payment arrangements	0	0
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Recognized compensation expense	500,000
Approximate compensation expenses	4,300,000
Weighted Average Remaining Contractual Life, Options outstanding	3 years 6 months
2009 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period					4 years
Options vested , description	Options granted generally vest over four years and vest at a rate of 25% upon the first anniversary of the issuance date and 1/36th per month thereafter
2014 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period	4 years
Options expiration period	10 years
Options vested , description	Options granted under the 2014 Plan have a contractual life of ten years and generally vest over four years and vest at a rate of 25% upon the first anniversary of the issuance date and 1/36th per month thereafter.
Number of shares reserved	4,100,000			4,100,000
Percentage of common stock issued and outstanding increase annually	4.50%
End date of automatic annual increase of shares reserved for issuance	Jan. 01, 2024
Common stock reserved for future issuance	991,401			991,401
2014 Plan [Member] | Incentive Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved	12,000,000			12,000,000
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved	150,000			150,000
Percentage of common stock issued and outstanding increase annually	1.00%
End date of automatic annual increase of shares reserved for issuance	Jan. 01, 2024
Additional shares issued	300,000
Voting power per share	Immediately after the grant would own stock possessing 5% or more of the total combined voting power or value of our common stock.
Percentage of stock possessing	5.00%
Rights to purchase stock that remains outstanding	$ 25,000			$ 25,000
Offerings of purchase periods	27 months
Maximum employee subscription rate	15.00%			15.00%
Maximum [Member] | 2009 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options expiration period					10 years
Minimum [Member] | 2009 Plan [Member] | Incentive Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Price of options granted, percentage	100.00%
Minimum [Member] | 2009 Plan [Member] | 10% Shareholders [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Price of options granted, percentage	110.00%
Minimum [Member] | 2014 Plan [Member] | Incentive Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Price of options granted, percentage	100.00%
Minimum [Member] | Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Price of options granted, percentage	85.00%