Warrant Liability (Details) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) $ / shares shares	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) $ / shares shares	Sep. 30, 2017 USD ($)
Warrants Liability [Abstract]
Proceeds from warrant exercise			$ 0	$ 24
Initial price of common stock offered (in dollars per share) | $ / shares	$ 15.00		$ 15.00
Warrant Liability [Roll Forward]
Balance as of beginning of period			$ 7,673
Change in fair value recognized	$ 4,116	$ 0	5,278	$ 309
Exercise of warrants			(12,951)
Balance as of end of period	$ 0		$ 0
Discount Rate [Member]
Warrants Liability [Abstract]
Measurement input of warrants		0.245		0.245
Volatility Rates [Member]
Warrants Liability [Abstract]
Measurement input of warrants		0.9		0.9
Perceptive Credit Opportunities Fund, LP [Member]
Warrants Liability [Abstract]
Number of shares received upon automatic exercise of warrant (in shares) | shares	863,400		863,400
Proceeds from warrant exercise			$ 116
Perceptive Credit Opportunities Fund, LP [Member] | Line of Credit [Member]
Warrants Liability [Abstract]
Warrant to purchase senior common equity interest ratio to fully diluted common units	4.50%		4.50%
Purchase price of warrant within first year of the loan	$ 3,000		$ 3,000
Purchase price of warrant after first year	5,000		5,000
Warrant liability, fair value	$ 5,800		$ 5,800