Tax Receivable Agreements (Details) - USD ($) $ in Thousands			1 Months Ended	12 Months Ended
	Jan. 01, 2018	Apr. 15, 2015	Feb. 28, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Aug. 31, 2017
Payment on applicable cash tax savings (as a percent)		85.00%
First payment due after filing of company's tax return							120 days
First payment made			$ 7,000
Deferred tax assets related to exchange of units		$ 220,800
Minimum tax receivable agreement obligation over the agreed period		300
Maximum tax receivable agreement obligation over the agreed period		$ 12,800
Period over which the obligations are to be settled		15 years
Reduction of paid-in capital for the difference between TRA liability and related deferred tax asset.		$ 19,900
Deferred tax asset recorded in connection with a stock offering								$ 10,800
Amount of payment liability pursuant to tax receivable agreements								9,300
Increase in additional paid-in capital related to tax receivable agreements								$ 1,500
U.S. federal statutory rate (as a percent)					35.00%	35.00%	35.00%
Reduction to additional paid-in capital as a result of differences between estimate and tax returns					$ 86,600
Deferred tax assets					101,600	$ 185,700
Tax receivable agreement obligations					$ 147,040	$ 231,404
Forecast
U.S. federal statutory rate (as a percent)	21.00%			21.00%