Shareholders' Equity - Controlled Equity Offering (Details) - USD ($)				3 Months Ended
	Jan. 19, 2016	Apr. 22, 2013	Apr. 18, 2013	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Class of Stock [Line Items]
Common stock aggregate offering price				$ 4,191		$ 4,191
Cantor Fitzgerald And Company | The Sales Agreement
Class of Stock [Line Items]
Common stock authorized for sale	$ 15,081,494		$ 25,000,000
Commission rate			3.00%
Common stock issued (in shares)		264,831
Controlled equity offering lock-up period	12 months
Stock offering, maximum public float	$ 75,000,000
Value of common stock available for sale under agreement				$ 14,300,000
Cantor Fitzgerald And Company | The Sales Agreement | Common Stock
Class of Stock [Line Items]
Common stock issued (in shares)				0	0
Cantor Fitzgerald And Company | The Sales Agreement | Offer and Sale
Class of Stock [Line Items]
Common stock aggregate offering price			$ 17,000,000