Revenue Recognition - Summary of Revenue Disaggregated by Program (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation Of Revenue [Line Items]
Revenues	$ 303,897	$ 151,467	$ 858,369	$ 453,261
Healthcare
Disaggregation Of Revenue [Line Items]
Revenues	159,979	151,467	473,987	453,261
Healthcare \| SilverSneakers
Disaggregation Of Revenue [Line Items]
Revenues	124,602	121,966	370,524	365,187
Healthcare \| Prime Fitness
Disaggregation Of Revenue [Line Items]
Revenues	30,499	25,374	88,993	75,321
Healthcare \| WholeHealth Living
Disaggregation Of Revenue [Line Items]
Revenues	4,752	4,106	13,783	12,550
Healthcare \| Other
Disaggregation Of Revenue [Line Items]
Revenues	$ 126	$ 21	$ 687	$ 203

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130543-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

Name:	us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration