Income Taxes - Federal Tax purpose (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended		12 Months Ended
	Oct. 06, 2016	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
U.S. Federal income tax rate (as a percent)				21.00%		21.00%
Deferred income taxes due to transfer of assets					$ 14,400
Deferred income tax expense from blended statutory income tax rates			$ 1,100
Income tax expense		$ 6,383		$ 9,900	37,497	$ 31,027
Effective tax rate (as a percent)				17.70%		18.50%
Current portion of liabilities under tax receivable agreement		$ 6,815			6,815		$ 9,446
Tax Receivable Agreement liability adjustment					8,477
Tax receivable agreement
Expected future tax benefits retained by the Company (as a percent)	15.00%
Reduction in tax receivable agreement liability due to reduction of future expected tax amortization					7,200
Reduction in tax receivable agreement liability due to change in state income tax rates					$ 1,100
Tax receivable agreement | CWGS, LLC
Units issued in exchange		0		42,200	5,725	215,486
Tax receivable agreement | Continuing Equity Owners and Crestview partners II GP LP
Payment, as percent of tax benefits (as a percent)	85.00%
CWH | CWGS, LLC
Ownership interest					42.00%		41.90%
Units held		37,377,004			37,377,004		37,192,364
Crestview Partners II GP LP | Tax receivable agreement
Liability under tax receivable agreement		$ 116,300			$ 116,300		$ 134,200
Current portion of liabilities under tax receivable agreement		$ 6,800			$ 6,800		$ 9,400