Organization and Business Operations - IPO (Details) - USD ($) $ / shares in Units, $ in Millions		9 Months Ended
	Aug. 16, 2017	Sep. 30, 2017	Sep. 30, 2016
Initial Public Offering
Net proceeds from initial public offering		$ 80.8
Repayments of long-term debt	$ 10.4	12.0	$ 2.0
Payment of offering related costs		$ 3.8
Payment of cash bonuses to certain employees	0.7
ESCO
Initial Public Offering
Cash consideration	$ 45.2
Class A Common Stock | ESCO
Initial Public Offering
Share price (in dollars per share)	$ 14.50
Class A Common Stock | IPO
Initial Public Offering
Stock issued (in shares)	5,862,069
Share price (in dollars per share)	$ 14.50
Gross proceeds from initial public offering	$ 85.0
Net proceeds from initial public offering	80.8
Underwriting discounts and commissions	4.2
Net proceeds from the initial public offering, after repayment of debt, funding of acquisition and other costs	20.7
Payment of offering related costs	$ 3.8