Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	Jan. 22, 2018	Dec. 31, 2017	Sep. 30, 2017
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
Preferred stock, par value		$ 0.001
Common stock, shares outstanding		74,917,876	74,785,426
Subsequent Events | Underwritten Public Offering
Class Of Stock [Line Items]
Common stock shares sold	11,500,000
Public offering price per share	$ 5.25
Net proceeds, after deducting underwriting commissions and discounts and offering expenses payable	$ 56.7
2004 Equity Incentive Plan, 2013 Equity Incentive Plan, and Inducement Grants
Class Of Stock [Line Items]
Common Stock, Share reserve for issuance		9,002,916