Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Proceeds from issuance of common stock from "at-the-market" facility, net				$ 19,206,000	$ 0
Shares of common stock ,reserved for issuance		11,413,298		11,413,298
Aggregate intrinsic value		$ 4,102,000		$ 4,102,000
Common stock, shares exercised				0	18,947
Option intrinsic value, exercised					$ 200,000
Net tax benefits related to exercised options				$ 0
Granted, Number of shares				1,155,900
Estimated fair value of stock option, vested				$ 10,900,000	10,400,000
Stock-based compensation expense		6,000,000	$ 5,269,000	$ 17,003,000	$ 15,128,000
Weighted average exercise price of options granted				$ 15.99
Non Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted, Number of shares				0	9,000
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average grant date fair value per share				$ 15.07	$ 17.83
Unrecognized stock-based compensation expense		22,800,000		$ 22,800,000
Unrecognized stock-based compensation weighted average recognition period				2 years 9 months 19 days
Aggregate intrinsic value		29,000,000		$ 29,000,000
Restricted stock units, settled				290,534	153,719
Restricted stock units, issued net of tax withholdings				51,592	10,898
Restricted stock units withheld for tax obligations				21,895	4,251
Restricted stock units withheld for tax obligations, value				$ 400,000	$ 75,000
Vested and Unvested Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation weighted average recognition period				2 years 7 months 7 days
Unrecognized stock-based compensation		$ 32,600,000		$ 32,600,000
2014 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock ,reserved for issuance		10,310,669		10,310,669
Aggregate number of awards available for grant to be issued		3,921,737		3,921,737
Outstanding options and RSUs		6,388,932		6,388,932
2014 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock ,reserved for issuance		827,629		827,629
Aggregate number of awards available for grant to be issued		827,630		827,630
Stock-based compensation expense				$ 400,000	$ 300,000
Shares purchased				43,962	0
Outside 2014 EIP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock ,reserved for issuance		275,000		275,000
Granted, Number of shares		145,000	0	275,000	0
Weighted average exercise price of options granted		$ 13.65		$ 13.96
Weighted average grant date fair value of options granted		$ 1,200,000		$ 2,200,000
At The Market Offering | Cowen
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares sold		655,876		1,349,865
Common stock average price		$ 15.55		$ 14.82
Proceeds from issuance of common stock from "at-the-market" facility, net		$ 10,200,000		$ 20,000,000
Net proceeds from sale of common stock after agent commissions and other offering expenses		9,900,000		19,200,000
Common stock value remained available to be sold		$ 55,000,000		$ 55,000,000
At The Market Offering | Cowen | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock aggregate offering price	$ 75,000,000
Percentage of commission to be paid on gross sales proceeds of common stock sold	3.00%