Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended
	Nov. 18, 2016	Nov. 30, 2016	Dec. 31, 2016	Sep. 30, 2016
Class Of Stock [Line Items]
Capital stock authorized for issuance			150,000,000
Common stock, shares authorized			145,000,000	145,000,000
Common stock, par value			$ 0.001	$ 0.001
Preferred stock, shares authorized			5,000,000	5,000,000
Preferred stock, par value			$ 0.001	$ 0.001
Common stock, shares outstanding			74,413,040	69,746,685
Preferred stock, shares outstanding			0	15,652
ARO-LPA Agreement | Amgen
Class Of Stock [Line Items]
Common stock shares sold	1,745,810
Common stock shares sold, price per share	$ 7.16
Net proceeds received		$ 12.5
Series C Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares converted			15,652
Common stock, issued upon conversion of preferred stock			2,670,990
Preferred stock, shares outstanding			0
2004 Equity Incentive Plan, 2013 Equity Incentive Plan, and Inducement Grants
Class Of Stock [Line Items]
Common Stock, Share reserve for issuance			8,100,085