Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)					12 Months Ended
	Feb. 05, 2020	Jan. 08, 2020	Jan. 02, 2018	May 11, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
Summary Of Significant Accounting Policies [Line Items]
Stock based compensation expenses					$ 6,341,000	$ 7,534,000	$ 8,454,000
Weighted average fair value of stock option granted					$ 2.47	$ 1.64	$ 3.94
Accumulated deficit					$ (684,125,000)	$ (566,329,000)	$ (712,442,000)
Transaction Price					$ 57,500,000
Changes in contract liability						(146,000)	(6,389,000)
Issuance of Common Stock to Underwriters				9,708,738	2,814,673
Net Proceeds from Underwriting					$ 6,085,000	47,101,000	47,270,000
Number of common Stock Sold				9,708,738	2,814,673
Net Proceeds from Sales					$ 6,085,000	47,101,000	47,270,000
Underwriting Agreement with Jefferies [Member]
Summary Of Significant Accounting Policies [Line Items]
Issuance of Common Stock to Underwriters	27,826,086
Net Proceeds from Underwriting	$ 85,000,000
Number of common Stock Sold	27,826,086
Net Proceeds from Sales	$ 85,000,000
Underwriting Agreement [Member]
Summary Of Significant Accounting Policies [Line Items]
Issuance of Common Stock to Underwriters	2,814,673
Net Proceeds from Underwriting	$ 13,000,000
Number of common Stock Sold	2,814,673
Net Proceeds from Sales	$ 13,000,000
Difference between revenue guidance in effect before and after topic 606
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit								$ 8,100,000
Research and Development Services Contract Term					9 years
Changes in contract liability			$ 8,100,000
Stock Options
Summary Of Significant Accounting Policies [Line Items]
Stock based compensation expenses					$ 4,000,000	3,000,000	2,500,000
Restricted Stock
Summary Of Significant Accounting Policies [Line Items]
Stock based compensation expenses					2,300,000	4,500,000	6,000,000
Restricted Stock Units (RSUs) [Member]
Summary Of Significant Accounting Policies [Line Items]
Stock based compensation expenses					$ 6,300,000	7,500,000	8,500,000
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment useful life					3 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment useful life					5 years
Subsequent Event
Summary Of Significant Accounting Policies [Line Items]
Issuance of Common Stock to Underwriters	2,814,673
Net Proceeds from Underwriting	$ 13,000,000
Number of common Stock Sold	2,814,673
Net Proceeds from Sales	$ 13,000,000
Subsequent Event | License Amendment Agreement
Summary Of Significant Accounting Policies [Line Items]
Expected cash payment payable		$ 600,000
Period for paying the estimated cash from the date of amendment		60 days
ASU 2014-09
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit							(720,573,000)
ASU 2014-09 | Difference between revenue guidance in effect before and after topic 606
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit							$ (8,131,000)
Changes in contract liability					$ 0	$ 0