Basis of Presentation - Contributions to Revenue and Receivables by Payor (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Net Revenue | Payor A
Accounts Receivable And Net Revenue [Line Items]
Concentration risk	12.00%	14.80%	14.30%	13.40%
Net Revenue | Payor B
Accounts Receivable And Net Revenue [Line Items]
Concentration risk	11.70%	18.40%	13.30%	16.90%
Net Revenue | Payor C
Accounts Receivable And Net Revenue [Line Items]
Concentration risk		12.70%	10.00%	13.10%
Net Revenue | Payor D
Accounts Receivable And Net Revenue [Line Items]
Concentration risk	12.00%	16.70%		15.60%
Net Revenue | Payor E
Accounts Receivable And Net Revenue [Line Items]
Concentration risk	19.90%		11.00%
Accounts Receivable | Payor E
Accounts Receivable And Net Revenue [Line Items]
Concentration risk			18.10%
Accounts Receivable | Payor F
Accounts Receivable And Net Revenue [Line Items]
Concentration risk			28.00%		34.10%
Accounts Receivable | Payor G
Accounts Receivable And Net Revenue [Line Items]
Concentration risk			29.10%		42.20%