Stockholders' Equity - July 2016 Aspire Common Stock Purchase Agreement (Details)		1 Months Ended	12 Months Ended		27 Months Ended
	Jul. 05, 2016 USD ($) shares	Jul. 31, 2016 USD ($) closing_price day $ / shares shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2018 USD ($) shares
Stockholders Equity Note [Line Items]
Transaction costs			$ 690,000	$ 1,392,000
Aspire Capital Fund, LLC [Member]
Stockholders Equity Note [Line Items]
Common stock purchase agreement, shares authorized, amount		$ 7,000,000
Common stock purchase agreement, term		24 months
Shares issued (in shares) | shares	5,063
Shares issued, value	$ 600,000
Issuance of common stock (in shares) | shares	253,165				500,000
Issuance of common stock, value	$ 1,000,000				$ 1,200,000
Transaction costs		$ 100,000
Common stock purchase agreement, number of closing prices averaged to determine sale price (in closing prices) | closing_price		3
Common stock purchase agreement, number of days prior to stock purchase date for stock price assessment (in days) | day		12
Sale price measurement period		12 days
Share price, floor price required to use committed equity financing (in usd per share) | $ / shares		$ 1
Common stock purchase agreement, VWAP purchase, share price threshold (higher than) (in usd per share) | $ / shares		$ 3
Common stock purchase agreement, VWAP purchase, percentage of shares traded		30.00%
Common stock purchase agreement, VWAP purchase, percentage of weighted average price		97.00%
Common stock purchase agreement, maximum amount of shares to be sold (in shares) | shares		1,200,000
Common stock purchase agreement, maximum amount of shares to be sold, percentage of outstanding shares		19.99%
Aspire Capital Fund, LLC [Member] | Common Stock
Stockholders Equity Note [Line Items]
Stocked issued during period, weighted average cost per share (in usd per share) | $ / shares		$ 3.82