Share-Based Payments - Additional Information (Detail) (USD $)	12 Months Ended			1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock incentive plan, reserved shares of common stock	2,928,474	10,136,128		10,136,128
Total intrinsic value of options vested and expected to vest	$ 8,000,000
Total intrinsic value of options exercised	921,000	170,000	29,000
Total fair value of employee options vested	1,300,000	40,000	9,000
Expected dividend yield	0.00%
Stock options granted	221,408
Option granted, weighted average exercise prices	$ 14.14
Total number of non-employee stock options outstanding	1,438,528	1,346,238		1,346,238
Total unrecognized compensation cost related to non-vested stock options and unvested restricted stock	2,700,000
Total unrecognized compensation cost related to non-vested stock options and unvested restricted stock, recognition period	2 years 6 months 15 days
Non-Employee Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock, issued	3,000	0
Restricted stock, granted			2,755
Granted purchase price			$ 0.06
Unvested stock, granted	1,000
Expense related to the restricted stock granted to non-employees	71,000	58,000	481,000
Performance-Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Expense related to the restricted stock granted to non-employees	293,000	106,000
Unrecognized compensation expense	2,100,000
Expected term (in years)	10 years
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense related to the restricted stock granted to non-employees	1,600,000	187,000	14,000
Expected term (in years)		6 years	6 years
Expected dividend yield	0.00%	0.00%	0.00%
Option granted, weighted average grant date fair value	$ 8.68	$ 4.07	$ 0.45
Non-employee Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	10 years	10 years	10 years
Expected dividend yield	0.00%	0.00%	0.00%
Stock options granted	0	231,968	31,496
Option granted, weighted average exercise prices		$ 1.77	$ 0.76
Total number of non-employee stock options outstanding	434,403
Expense related to options granted to employees	$ 504,000	$ 486,000	$ 45,000
2009 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of fair value exercise price grant date of incentive stock options granted to 10% shareholder employees	110.00%
Award vesting period	4 years
Expected term (in years)	10 years
Stock incentive plan, reserved shares of common stock		1,347,821		1,347,821
Stock incentive plan, shares remained available for future issuance		1,586		1,586
2009 Stock Incentive Plan [Member] | Cliff for New Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	1 year
Stock Incentive Plan 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock incentive plan, reserved shares of common stock		708,661		708,661
Stock incentive plan, annual increase in reserved shares of common stock				1,102,362
Stock incentive plan, annual increase in reserved shares as percentage of outstanding common stock				4.00%