Stockholders' Equity (Details)			6 Months Ended	12 Months Ended
	Nov. 18, 2015 USD ($)	Jul. 31, 2015 USD ($) director $ / shares shares	Jun. 30, 2018 vote $ / shares shares	Nov. 17, 2016 USD ($) shares	Dec. 31, 2015 shares	Dec. 31, 2017 $ / 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)			50,486,962			50,340,853
Number of shares issuable upon exercise of warrants (in shares)			15,983,072
Exercise price (in dollars per share) | $ / shares			$ 11.5
Number of warrants outstanding (in shares)			15,983,072
Shares authorized (in shares) | $	$ 10,000,000
Stock repurchase period	1 year
Shares repurchased during period (in shares)				661,381
Value of treasury stock acquired | $				$ 3,900,000
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
Shares issued during period (in shares)		4,878,048
Issue price of stock (in dollars per share) | $ / shares		$ 10.25
Value of shares issued during period | $		$ 50,000,000