Segment Reporting (Details)		3 Months Ended								12 Months Ended
		Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment										2
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue		$ 193,104,000	$ 149,947,000	$ 144,298,000	$ 139,714,000	$ 113,729,000	$ 107,912,000	$ 107,071,000	$ 106,238,000	$ 627,063,000	$ 434,950,000	$ 254,188,000
Adjusted EBITDA										23,225,000	(2,204,000)	(21,407,000)
Operating segments | Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										547,431,000	434,950,000	254,188,000
Adjusted EBITDA										21,310,000	(2,204,000)	(21,407,000)
Operating segments | True Health
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										94,763,000	0	0
Adjusted EBITDA										1,915,000	0	0
Intersegment eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										(15,131,000)	0	0
Adjusted EBITDA										23,225,000	(2,204,000)	(21,407,000)
Transformation services
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										36,571,000	29,466,000	38,434,000
Total revenue	[1]									32,916,000	29,466,000	38,320,000
Transformation services | Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										32,916,000
Transformation services | Operating segments | Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										36,571,000	29,466,000	38,434,000
Transformation services | Operating segments | True Health
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										0	0	0
Transformation services | Intersegment eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										0	0	0
Platform and operations services
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										501,894,000	406,951,000	217,844,000
Total revenue	[1]									500,190,000	405,484,000	215,868,000
Platform and operations services | Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										492,568,000
Platform and operations services | Operating segments | Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										516,219,000	406,951,000	217,844,000
Platform and operations services | Operating segments | True Health
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										0	0	0
Platform and operations services | Intersegment eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										(14,325,000)	0	0
Services Revenue
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										538,465,000	436,417,000	256,278,000
Services Revenue | Operating segments | Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										552,790,000	436,417,000	256,278,000
Services Revenue | Operating segments | True Health
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										0	0	0
Services Revenue | Intersegment eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										(14,325,000)	0	0
Premiums
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										93,957,000	0	0
Balances without adoption of ASC 606
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										632,422,000	436,417,000	256,278,000
Balances without adoption of ASC 606 | Operating segments | Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										552,790,000	436,417,000	256,278,000
Balances without adoption of ASC 606 | Operating segments | True Health
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										94,763,000	0	0
Balances without adoption of ASC 606 | Intersegment eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										(15,131,000)	0	0
Balances without adoption of ASC 606 | Transformation services
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										35,238,000
Balances without adoption of ASC 606 | Platform and operations services
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										497,284,000
Balances without adoption of ASC 606 | Premiums
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										93,957,000
Balances without adoption of ASC 606 | Premiums | Operating segments | Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										0
Balances without adoption of ASC 606 | Premiums | Operating segments | True Health
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										94,763,000
Balances without adoption of ASC 606 | Premiums | Intersegment eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted Revenue										(806,000)
Difference between Revenue Guidance in Effect before and after Topic 606
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										(861,000)	(1,467,000)	(2,090,000)
Difference between Revenue Guidance in Effect before and after Topic 606 | Operating segments | Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										(861,000)	(1,467,000)	(2,090,000)
Difference between Revenue Guidance in Effect before and after Topic 606 | Operating segments | True Health
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										0	0	0
Difference between Revenue Guidance in Effect before and after Topic 606 | Intersegment eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										0	$ 0	0
Difference between Revenue Guidance in Effect before and after Topic 606 | Transformation services | Operating segments | Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										0		100,000
Difference between Revenue Guidance in Effect before and after Topic 606 | Platform and operations services | Operating segments | Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue												$ 2,000,000
Difference between Revenue Guidance in Effect before and after Topic 606 | Premiums | Operating segments | Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										0
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										(4,498,000)
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09 | Operating segments | Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										(4,498,000)
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09 | Operating segments | True Health
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										0
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09 | Intersegment eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										0
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09 | Transformation services
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										(2,322,000)
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09 | Transformation services | Operating segments | Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										3,700,000
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09 | Platform and operations services
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										2,906,000
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09 | Platform and operations services | Operating segments | Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenue										$ 800,000

[1] (1) See Note 17 for amounts related to related parties included in these line items.