Stock-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Aug. 31, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested exercisable shares		775,098		775,098		469,000
Unvested exercisable shares, vesting period				2 years 7 months 6 days
Unvested options exercised				0	0
Weighted-average grant-date fair value of stock options granted				$ 4.68	$ 3.72
Total intrinsic value of options exercised				$ 7,600,000	$ 4,200,000
Total fair value of options vested				7,400,000	2,900,000
Compensation expense recognized		$ 4,006,000	$ 1,727,000	10,427,000	$ 6,037,000
Total unrecognized compensation cost		24,000,000		$ 24,000,000		$ 12,100,000
Weighted-average period of recognition				2 years 10 months 24 days		2 years 9 months 18 days
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance	1,000,000
Minimum annual increase included in common stock reserved for future issuance as of first day of each fiscal year	5,000,000
Minimum percentage of annual increase included in common stock reserved for future issuance as of last day of immediately preceding fiscal year	2.00%
Terms of shares available for issuance				The number of shares of common stock available for sale under the Company’s ESPP will also include an annual increase on the first day of each fiscal year beginning on January 1, 2016, equal to the least of (i) 5,000,000 shares (ii) 2% of the common stock as of the last day of the immediately preceding fiscal year or (iii) such other amount as the Company’s board of directors may determine.
Maximum deductible value of shares available for employee to purchase per calendar year	$ 25,000
Maximum percentage in payroll deductions to acquire shares of common stock	15.00%
Maximum number of shares available for employee to purchase per offering period	2,000
Term of offering period				Employees are offered shares bi-annually through two six month offering periods, which begin on the first trading day on or after May 15 and November 15 of each year. The first offering period begins in November 2015.
Employee Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation expense recognized		$ 100,000		$ 1,600,000
Sale of shares		125,100		1,131,028
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option plan, number of shares granted				757,000		947,342
Vesting starting period				2014-08
Vesting ending period				2017-08
Stock option plan, number of additional shares available for grant						372,342
Performance-based Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation expense recognized		$ 300,000		$ 300,000