Number of new stock issued during the period.

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Name:	us-gaap_StockIssuedDuringPeriodSharesNewIssues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Common Stock - Additional Information (Details) - At-the-Market Offering - 2017 Sales Agreement - Cowen and Company, LLC - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
	Aug. 31, 2017	Mar. 31, 2019	Dec. 31, 2018
Class Of Stock [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
Maximum
Class Of Stock [Line Items]
Aggregate offering price from offer and sale of common stock	$ 100,000,000