Earnings (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2017	[1]	Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016	[2]	Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator [Abstract]
Income from continuing operations attributable to Tivity Health, Inc. - numerator for earnings per share	$ 8,624		$ 19,886		$ 17,240		$ 15,481		$ 12,125		$ 4,799		$ 19,962		$ 19,208		$ 61,230	$ 56,091	$ 43,634
Net income (loss) from discontinued operations attributable to Tivity Health, Inc. - numerator for earnings (loss) per share	(141)		6,519		(3,673)		(220)		(5,225)		48,995		(195,558)		(33,417)		2,485	(185,202)	(74,581)
Net income (loss) attributable to Tivity Health, Inc.	$ 8,483		$ 26,405		$ 13,567		$ 15,261		$ 6,900		$ 53,794		$ (175,596)		$ (14,209)		$ 63,715	$ (129,111)	$ (30,947)
Denominator [Abstract]
Shares used for basic income (loss) per share (in shares)																	39,357	36,999	35,832
Effect of dilutive stock options and restricted stock units outstanding [Abstract]
Shares used for diluted income (loss) per share (in shares)																	42,547	38,075	36,854
Earnings (loss) per share attributable to Tivity Health, Inc. - basic [Abstract]
Continuing operations (in dollars per share)	$ 0.22	[3]	$ 0.50	[3]	$ 0.44	[3]	$ 0.40	[3]	$ 0.31	[3]	$ 0.13	[3]	$ 0.55	[3]	$ 0.53	[3]	$ 1.56	$ 1.52	$ 1.22
Discontinued operations (in dollars per share)	0	[3]	0.17	[3]	(0.09)	[3]	(0.01)	[3]	(0.14)	[3]	1.32	[3]	(5.41)	[3]	(0.93)	[3]	0.06	(5.01)	(2.08)
Net income (loss) (in dollars per share)	0.21	[3],[4]	0.67	[3],[4]	0.35	[3],[4]	0.39	[3],[4]	0.18	[3],[4]	1.45	[3],[4]	(4.85)	[3],[4]	(0.39)	[3],[4]	1.62	(3.49)	(0.86)
Earnings (loss) per share attributable to Tivity Health, Inc. - diluted [Abstract]
Continuing operations (in dollars per share)	0.20	[3]	0.46	[3]	0.41	[3]	0.38	[3]	0.30	[3]	0.12	[3]	0.54	[3]	0.52	[3]	1.44	1.47	1.18
Discontinued operations (in dollars per share)	0	[3]	0.15	[3]	(0.09)	[3]	(0.01)	[3]	(0.13)	[3]	1.28	[3]	(5.25)	[3]	(0.91)	[3]	0.06	(4.86)	(2.02)
Net income (loss) (in dollars per share)	$ 0.20	[3],[4]	$ 0.61	[3],[4]	$ 0.32	[3],[4]	$ 0.38	[3],[4]	$ 0.17	[3],[4]	$ 1.40	[3],[4]	$ (4.72)	[3],[4]	$ (0.39)	[3],[4]	$ 1.50	$ (3.39)	$ (0.84)
Non-Qualified Stock Options [Member]
Effect of dilutive stock options and restricted stock units outstanding [Abstract]
Effect of dilutive stock options and restricted stock units outstanding (in shares)																	436	344	568
Restricted Stock Units [Member]
Effect of dilutive stock options and restricted stock units outstanding [Abstract]
Effect of dilutive stock options and restricted stock units outstanding (in shares)																	549	538	364
Performance Stock Units [Member]
Effect of dilutive stock options and restricted stock units outstanding [Abstract]
Effect of dilutive stock options and restricted stock units outstanding (in shares)																	0	0	25
Market Stock Units [Member]
Effect of dilutive stock options and restricted stock units outstanding [Abstract]
Effect of dilutive stock options and restricted stock units outstanding (in shares)																	496	194	10
Warrants Related to Cash Convertible Notes [Member]
Effect of dilutive stock options and restricted stock units outstanding [Abstract]
Effect of dilutive stock options and restricted stock units outstanding (in shares)																	1,709
CareFirst Warrants [Member]
Effect of dilutive stock options and restricted stock units outstanding [Abstract]
Effect of dilutive stock options and restricted stock units outstanding (in shares)																	0	0	55
Non-Qualified Stock Options [Member]
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)																	4	708	903
Restricted Stock Units [Member]
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)																	12	333	220
Performance Stock Units [Member]
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)																	0	0	1
Market Stock Units [Member]
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)																	6	2	0
Warrants Related to Cash Convertible Notes [Member]
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)																	0	7,707	7,707
CareFirst Convertible Note [Member]
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)																	0	0	892
CareFirst Warrants [Member]
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)																	0	0	263

[1] The Tax Act was signed into law during the fourth quarter of 2017, and we incurred a non-cash charge of $7.4 million during the quarter related to both the re-measurement of our deferred tax assets to the lower tax rate and the requirement to recalculate the impact of repatriation of our foreign earnings, which occurred earlier in the year, under provisions of the new law.

[2] Income from continuing operations for the fourth quarter of 2016 includes the impact of a $2.2 million out of period adjustment to decrease depreciation expense included in continuing operations (with a corresponding increase to depreciation expense included in discontinued operations). This adjustment was recorded after having completed our asset separation analysis and related to the correction of our previous allocation of 2016 depreciation expense between continuing and discontinued operations. The previous interim periods in 2016 were not materially misstated, nor is the correction material to the interim results for the fourth quarter of 2016.

[3] 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.

[4] Figures may not add due to rounding.