Stockholders' Equity (Details)		9 Months Ended	12 Months Ended
	Jul. 31, 2015 director shares	Sep. 30, 2019 vote $ / shares shares	Dec. 31, 2015 shares	Dec. 31, 2018 $ / shares shares	Feb. 28, 2014 shares
Class of Warrant or Right [Line Items]
Authorized common stock (in shares)		400,000,000		400,000,000
Par value of common stock (in dollars per share) | $ / shares		$ 0.0001		$ 0.0001
Number of votes entitled by holders of common stock for each share of common stock | vote		1
Common stock, shares outstanding (in shares)		50,931,578		50,410,192
Number of shares issuable upon exercise of warrants (in shares)		15,983,072
Exercise price (in dollars per share) | $ / shares		$ 11.50
Number of warrants outstanding (in shares)		15,983,072
Rohm and Haas
Class of Warrant or Right [Line Items]
Number of shares of Series A Preferred Stock issued as condition to consummation of business combination (in shares)	1
Number of directors preferred stockholder is entitled to appoint if minimum ownership percentage of common stock is maintained | director	1
Minimum percentage of outstanding shares of voting and non-voting common stock to be held to entitle preferred stockholder to appoint director	10.00%
Public
Class of Warrant or Right [Line Items]
Number of warrants outstanding (in shares)					9,823,072
Number of warrants repurchased (in shares)			1,201,928
Private placement
Class of Warrant or Right [Line Items]
Number of warrants outstanding (in shares)					6,160,000