Summary of Significant Accounting Policies - Credit Risk, Restricted Cash, and Allowance for Doubtful Accounts (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) financial_institution	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Concentrations of Credit Risk and Other Risks and Uncertainties
Number of major financial institutions with which the company's cash and cash equivalents are deposited (in financial institutions) | financial_institution	1
Restricted Cash
Long term deposit consisting of letter of credit serving as security for lease | $	$ 603	$ 603	$ 603
Revenue | Revenue concentration risk
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentration risk	37.00%	41.00%	40.00%
Revenue | Revenue concentration risk | Medicare
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentration risk	26.00%	29.00%	26.00%
Revenue | Revenue concentration risk | United Healthcare
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentration risk	11.00%	12.00%	14.00%
Accounts receivable | Gross receivables concentration risk | Medicare
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentration risk	15.00%	20.00%
Accounts receivable | Gross receivables concentration risk | Johnson and Johnson Services, Inc.
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentration risk	10.00%	0.00%
Accounts receivable | Gross receivables concentration risk | United Healthcare
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentration risk	9.00%	11.00%