Earnings (Loss) Per Share - Reconciliation of the Numerator and Denominator of Basic and Diluted Earnings (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2020	[1]	Sep. 30, 2020		Jun. 30, 2020		Mar. 31, 2020		Dec. 31, 2019	[2]	Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019	[3]	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Numerator [Abstract]
Net income (loss) from discontinued operations attributable to Tivity Health, Inc. - numerator for earnings (loss) per share	$ (26,260)		$ (59,168)		$ 11,309		$ (206,381)		$ (340,943)		$ (2,769)		$ 7,299		$ 4,375		$ (280,500)		$ (332,038)		$ 901
Net income (loss)	(11,618)		(42,418)		28,511		(198,106)		(323,090)		13,919		18,136		4,214		(223,631)		(286,821)		98,803
Income from continuing operations attributable to Tivity Health, Inc. - numerator for earnings (loss) per share	$ 14,642		$ 16,750		$ 17,202		$ 8,275		$ 17,853		$ 16,688		$ 10,837		$ (161)		$ 56,869		$ 45,217		$ 97,902
Denominator [Abstract]
Shares used for basic income (loss) per share																	48,746		46,509		40,078
Effect of dilutive stock options and restricted stock units outstanding [Abstract]
Shares used for diluted income (loss) per share																	49,217		47,103		43,073
Earnings (loss) per share attributable to Tivity Health, Inc. - basic [Abstract]
Continuing operations (in dollars per share)	$ 0.30	[4]	$ 0.34	[4]	$ 0.35	[4]	$ 0.17	[4]	$ 0.37	[4]	$ 0.35	[4]	$ 0.23	[4]			$ 1.17		$ 0.97		$ 2.44
Discontinued operations (in dollars per share)	(0.54)	[4]	(1.21)	[4]	0.23	[4]	(4.25)	[4]	(7.06)	[4]	(0.06)	[4]	0.15	[4]	$ 0.10	[4]	(5.75)		(7.14)		0.02
Net income (loss)	(0.24)	[4]	(0.87)	[4]	0.59	[4]	(4.08)	[4]	(6.69)	[4]	0.29	[4]	0.38	[4]	0.10	[4]	(4.59)	[5]	(6.17)	[5]	2.47	[5]
Earnings (loss) per share attributable to Tivity Health, Inc. - diluted [Abstract]
Continuing operations (in dollars per share)	0.29	[4]	0.34	[4]	0.35	[4]	0.17	[4]	0.37	[4]	0.34	[4]	0.22	[4]			1.16		0.96		2.27
Discontinued operations (in dollars per share)	(0.53)	[4]	(1.20)	[4]	0.23	[4]	(4.22)	[4]	(6.97)	[4]	(0.06)	[4]	0.15	[4]	0.10	[4]	(5.70)		(7.05)		0.02
Net income (loss)	$ (0.23)	[4]	$ (0.86)	[4]	$ 0.58	[4]	$ (4.05)	[4]	$ (6.61)	[4]	$ 0.29	[4]	$ 0.37	[4]	$ 0.10	[4]	$ (4.54)		$ (6.09)		$ 2.29
Non-Qualified Stock Options
Effect of dilutive stock options and restricted stock units outstanding [Abstract]
Effect of dilutive stock options and restricted stock units outstanding (in shares)																	29		90		264
Restricted Stock Units (RSUs)
Effect of dilutive stock options and restricted stock units outstanding [Abstract]
Effect of dilutive stock options and restricted stock units outstanding (in shares)																	412		489		299
Warrants Related to Cash Convertible Notes
Effect of dilutive stock options and restricted stock units outstanding [Abstract]
Effect of dilutive stock options and restricted stock units outstanding (in shares)																					2,013
Market Stock Units
Effect of dilutive stock options and restricted stock units outstanding [Abstract]
Effect of dilutive stock options and restricted stock units outstanding (in shares)																	1				419
Performance-Based Stock Units
Effect of dilutive stock options and restricted stock units outstanding [Abstract]
Effect of dilutive stock options and restricted stock units outstanding (in shares)																	29		15
Non-Qualified Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Dilutive securities outstanding not included in the computation of earnings (loss) per share because their effect is anti-dilutive (in shares)																	186		70		56
Restricted Stock Units (RSUs)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Dilutive securities outstanding not included in the computation of earnings (loss) per share because their effect is anti-dilutive (in shares)																	242		192		36
Restricted Stock Awards
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Dilutive securities outstanding not included in the computation of earnings (loss) per share because their effect is anti-dilutive (in shares)																	26		102
Performance-Based Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Dilutive securities outstanding not included in the computation of earnings (loss) per share because their effect is anti-dilutive (in shares)																	24

[1] Income from continuing operations for the fourth quarter of 2020 includes strategic project costs, CEO transition costs, and acquisition and integration costs of $2.3 million, $1.0 million, and $0.6 million, respectively, each of which were primarily recorded to selling, general, and administrative expenses.

[2] Income from continuing operations for the fourth quarter of 2019 includes acquisition, integration, and project costs totaling $4.3 million, which were primarily recorded to selling, general, and administrative expenses.

[3] The impact of potentially dilutive securities for the three months ended March 31, 2019 was not considered because the impact on continuing operations would be anti-dilutive.

[4] We calculated earnings per share for each of the quarters based on the weighted average number of shares and dilutive securities outstanding for each period. Accordingly, the sum of the quarters may not necessarily be equal to the full year income per share.

[5] Figures may not add due to rounding.