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Subsequent Events (Details) - Common Stock [Member] - USD ($) $ / shares in Units, $ in Thousands	2 Months Ended	12 Months Ended
	Feb. 20, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock Transactions [Abstract]
Number of shares of common stock sold (in shares)		7,510,555	730,444	4,760,594
ATM Agreement [Member]
Stock Transactions [Abstract]
Number of shares of common stock sold (in shares)		7,510,555	730,444	4,760,594
Average sales price per common share (in dollars per share)		$ 3.71	$ 5.19	$ 4.16
Aggregate proceeds from sales of common stock		$ 27,837	$ 3,790	$ 19,791
Sales commissions, fees and other costs associated with issuance of common stock		$ 785	$ 113	$ 594
Subsequent Event [Member] | ATM Agreement [Member]
Stock Transactions [Abstract]
Number of shares of common stock sold (in shares)	560,338
Average sales price per common share (in dollars per share)	$ 5.24
Aggregate proceeds from sales of common stock	$ 2,936
Sales commissions, fees and other costs associated with issuance of common stock	$ 88

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