Stockholders' Equity - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended	9 Months Ended		14 Months Ended
	Aug. 31, 2017	May 31, 2016	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2017
Stockholders' Equity [Line Items]
Net proceeds from issuance of common stock, after deducting commissions and expenses payable					$ 77,156,000
At-the-Market Offering | 2017 Sales Agreement | Cowen and Company, LLC
Stockholders' Equity [Line Items]
Commission on sales of common stock, percentage	3.00%
Issuance of common stock (in shares)			0	0
Aggregate offering available for issuance of common stock				$ 81,500,000
At-the-Market Offering | 2017 Sales Agreement | Cowen and Company, LLC | Maximum
Stockholders' Equity [Line Items]
Aggregate offering price from offer and sale of common stock	$ 100,000,000
At-the-Market Offering | 2016 Sales Agreement | Cowen and Company, LLC
Stockholders' Equity [Line Items]
Commission on sales of common stock, percentage		3.00%
Issuance of common stock (in shares)		8,350,018
Net proceeds from issuance of common stock, after deducting commissions and expenses payable						$ 97,300,000
Amounts remaining for future sales		$ 0