Long-term Debt - Series C Narrative (Details) - $ / shares	1 Months Ended
	Apr. 30, 2019	Jul. 31, 2017	Oct. 31, 2015	Sep. 30, 2019	Dec. 31, 2018	Apr. 30, 2016
IPO
Class of Stock [Line Items]
Temporary equity, shares issued (in shares)	6,000,000
Stock issued, price per share (in USD per share)	$ 20.00			$ 20.00
Preferred Stock Warrants
Class of Stock [Line Items]
Warrants outstanding (in shares)			163,877	0	2,672,502
Warrant exercise price (in USD per share)						$ 6.11
Series C
Class of Stock [Line Items]
Temporary equity, shares issued (in shares)		163,877	327,759
Stock issued, price per share (in USD per share)		$ 6.11	$ 6.11