Basis of Presentation - Contributions to Revenue and Receivables by Payor (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Net Revenue | Payor A
Accounts Receivable And Net Revenue [Line Items]
Concentration risk	13.70%	11.30%	15.80%
Net Revenue | Payor B
Accounts Receivable And Net Revenue [Line Items]
Concentration risk	12.60%	16.60%	14.30%	15.70%
Net Revenue | Payor C
Accounts Receivable And Net Revenue [Line Items]
Concentration risk	10.50%	11.60%	11.70%	13.30%
Net Revenue | Payor D
Accounts Receivable And Net Revenue [Line Items]
Concentration risk	13.70%	17.90%		14.90%
Accounts Receivable | Payor E
Accounts Receivable And Net Revenue [Line Items]
Concentration risk			29.00%		34.10%
Accounts Receivable | Payor F
Accounts Receivable And Net Revenue [Line Items]
Concentration risk			34.00%		42.20%