Common Stock (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) Vote $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Aug. 31, 2018 USD ($)	Jul. 30, 2018 USD ($)	Mar. 08, 2018 USD ($)	Aug. 31, 2015 USD ($)
Common Stock [Abstract]
Common stock, shares authorized (in shares) | shares	100,000,000	100,000,000
Common stock, par value (in dollars per share) | $ / shares	$ 0.0001	$ 0.0001
Common Stock [Member]
Common Stock [Abstract]
Common stock, voting rights	Each share of common stock has the right to one vote
Number of votes entitled to each share of common stock | Vote	1
Common stock, shares authorized (in shares) | shares	100,000,000
Common stock, par value (in dollars per share) | $ / shares	$ 0.0001
Number of shares of common stock sold (in shares) | shares	7,510,555	730,444	4,760,594
Universal Shelf Registration Statement [Member] | Common Stock [Member] | Maximum [Member]
Common Stock [Abstract]
Securities offered for sale, aggregate value					$ 100,000		$ 100,000
ATM Agreement [Member] | Common Stock [Member]
Common Stock [Abstract]
Aggregate value of common stock available for offer and sale	$ 37,458
Number of shares of common stock sold (in shares) | shares	7,510,555	730,444	4,760,594
Average sales price per common share (in dollars per share) | $ / shares	$ 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
ATM Agreement [Member] | Common Stock [Member] | Maximum [Member]
Common Stock [Abstract]
Securities offered for sale, aggregate value				$ 50,000		$ 50,000	$ 35,000