Summary of Significant Accounting Policies - Intangible Assets (Details)	1 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Noncompete Agreements
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life		5 years
Minimum | Trade names
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life		5 years
Minimum | Employment Contracts
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life		9 years
Maximum | Trade names
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life		15 years
Maximum | Employment Contracts
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life		11 years
Regular Member
Finite-Lived Intangible Assets [Line Items]
Average member life	26 months	26 months	25 months	22 months