Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Millions			1 Months Ended		3 Months Ended	12 Months Ended
	Apr. 01, 2019	Mar. 20, 2019	Apr. 30, 2019	Jul. 31, 2018	Mar. 31, 2019	Dec. 31, 2018
Subsidiary, Sale of Stock [Line Items]
CW Unit redemptions					(43,820)	(7,068)
Subsequent event
Subsidiary, Sale of Stock [Line Items]
CW Unit redemptions			400,000
Distribution received from subsidiary			$ 5.8
July 2018 follow-on offering
Subsidiary, Sale of Stock [Line Items]
CW Unit redemptions				(11,196,562)
Class A Common Stock
Subsidiary, Sale of Stock [Line Items]
Common stock, par value					$ 0.01	$ 0.01
Class A Common Stock | Subsequent event
Subsidiary, Sale of Stock [Line Items]
Number of shares issued			400,000
Class B Common Stock
Subsidiary, Sale of Stock [Line Items]
Common stock redeemed (in shares)		8,473,913
Common stock, par value			$ 0.01		$ 0.01	$ 0.01
Class B Common Stock | Subsequent event
Subsidiary, Sale of Stock [Line Items]
Common stock redeemed (in shares)	400,000
Number of shares canceled			400,000
Cactus LLC
Subsidiary, Sale of Stock [Line Items]
Distribution received from subsidiary					$ 0.2
Cactus LLC | Subsequent event
Subsidiary, Sale of Stock [Line Items]
Distributions to LLC members made by subsidiary			$ 3.6