Intangible Assets and Goodwill - Intangible Assets Subject to and Not Subject to Amortization (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 08, 2019	[1]	Dec. 31, 2018
Finite Lived Intangible Assets [Line Items]
Total intangible assets, Fair Value	$ 975,729			$ 29,049
Goodwill	780,351			$ 334,680
Nutrisystem, Inc.
Finite Lived Intangible Assets [Line Items]
Intangible assets subject to amortization, Fair Value	148,000
Total intangible assets, Fair Value	948,000
Goodwill	445,671	$ 445,671
Nutrisystem, Inc. | Tradename - Nutrisystem
Finite Lived Intangible Assets [Line Items]
Intangible assets not subject to amortization:	800,000
Tradename - Nutrisystem | Nutrisystem, Inc.
Finite Lived Intangible Assets [Line Items]
Intangible assets subject to amortization, Fair Value	$ 9,000
Intangible assets subject to amortization, Fair Value, Estimated Useful Life	15 years
Customer list | Nutrisystem, Inc.
Finite Lived Intangible Assets [Line Items]
Intangible assets subject to amortization, Fair Value	$ 125,000
Intangible assets subject to amortization, Fair Value, Estimated Useful Life	7 years
Retail customer relationship | Nutrisystem, Inc.
Finite Lived Intangible Assets [Line Items]
Intangible assets subject to amortization, Fair Value	$ 8,000
Intangible assets subject to amortization, Fair Value, Estimated Useful Life	10 years
Noncompetition agreements | Nutrisystem, Inc.
Finite Lived Intangible Assets [Line Items]
Intangible assets subject to amortization, Fair Value	$ 6,000
Intangible assets subject to amortization, Fair Value, Estimated Useful Life	5 years

[1] Goodwill represents the excess of merger consideration over the preliminary fair value of the underlying assets acquired and liabilities assumed. Goodwill is attributable to the assembled workforce of experienced personnel at Nutrisystem and synergies expected to be achieved from the combined operations of Tivity Health and Nutrisystem.