Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Feb. 11, 2018
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Common Stock, Shares, Outstanding	74,889,772								74,889,772
Numerator:
Net income after IPO and Reorganization	$ 16,924	$ 18,672	$ 12,334	$ 3,753					$ 51,683
Class A Common Stock
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Common Stock, Shares, Outstanding	37,653,630								37,653,630		0
Denominator:
Weighted average Class A Shares Outstanding - diluted									32,695,000
Earnings per Class A Share - basic	$ 0.45	$ 0.52	$ 0.47	$ 0.14					$ 1.60
Earnings per Class A Share - diluted	$ 0.44	$ 0.52	$ 0.46	$ 0.14					$ 1.58
Class B Common Stock
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Common Stock, Shares, Outstanding	37,236,142								37,236,142		0
Denominator:
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									37,236,142