Stock-Based Compensation - Additional Information (Detail)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016 USD ($) shares	Sep. 30, 2015 USD ($) Milestone	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	Dec. 31, 2015 shares	Jul. 02, 2014 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation granted under plan vest period			4 years
Share based compensation, vest period			1 year
Share based compensation, term of plan			10 years
Stock-based compensation expense | $	$ 4,748,000	$ 4,407,000	$ 12,927,000	$ 11,154,000
Milestone expense | $	$ 0		$ 0
Weighted average grant date fair value per share | $ / shares			$ 23.32	$ 33.44
Share option, forfeiture rate			11.20%	10.00%
Options to Purchase Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option grant			1,213,068
Total number of shares reserved under equity plan , outstanding grant	4,061,280		4,061,280		3,002,809
Total unrecognized stock-based compensation expense | $	$ 40,000,000		$ 40,000,000
Weighted average period of unrecognized compensation costs			2 years 9 months 15 days
Total fair value of shares vested | $			$ 14,900,000	$ 7,300,000
Intrinsic value of options exercised | $			2,600,000	28,200,000
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized stock-based compensation expense | $	$ 8,500,000		$ 8,500,000
Number of shares outstanding unvested stock options	429,815		429,815
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense | $	$ 4,000	$ 100,000	$ 35,000	$ 200,000
Total unrecognized stock-based compensation expense | $	$ 1,000		$ 1,000
Weighted average period of unrecognized compensation costs			1 month 17 days
Issued, Shares-Restricted stock			0	0
Stock repurchased, shares			0	0
Share-based Compensation Award, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, vesting percentage			25.00%
2011 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option grant			0
2014 Stock Option Plan and 2011 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of shares reserved under equity plan , outstanding grant	4,061,280		4,061,280
Common stock available for issuance under 2014 Stock Option Plan	885,723		885,723
2014 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for issuance under 2014 Stock Option Plan					1,154,653
Percentage of increase on issued and outstanding shares of Common stock					4.00%
Milestones achieved | Milestone		1
Percentage of performance based option grants that were achieved					35.00%
2014 Stock Option Plan [Member] | Performance Milestone [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options with performance-based criteria			74,039	497,100
Stock-based compensation expense | $		$ 1,400,000		$ 4,800,000
2014 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock initially authorized for issuance under this plan						282,000
Number of shares issued under the plan			14,351