Revenue Recognition - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 211,315	$ 228,545
Healthcare insurers
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	100,953	112,696
Government payers
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	67,136	77,053
Client payers
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	37,529	33,939
Patients
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 5,697	$ 4,857