NET INCOME (LOSS) PER SHARE - Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Aug. 07, 2017
Numerator:
Net income (loss) attributable to Innoviva stockholders, basic	$ 58,385	$ 23,767	$ 35,146	$ 16,845					$ 134,143	$ 59,536	$ (18,760)
Add: interest expense on 2023 Notes									5,647	5,790	0
Net income (loss) attributable to Innoviva stockholders, diluted									$ 139,790	$ 65,326	$ (18,760)
Denominator:
Weighted-average shares used to compute basic net income (loss) per share attributable to Innoviva stockholders									106,945,000	110,280,000	115,372,000
Dilutive effect of 2023 Notes									12,189,000	12,541,000	0
Dilutive effect of options and awards granted under equity incentive plan and employee stock purchase plan									732,000	412,000	0
Weighted-average shares used to compute diluted net income (loss) per share attributable to Innoviva stockholders									119,866,000	123,233,000	115,372,000
Net income (loss) per share attributable to Innoviva stockholders
Basic net income per share	$ 0.55	$ 0.22	$ 0.33	$ 0.16	$ 0.24	$ 0.14	$ 0.13	$ 0.04	$ 1.25	$ 0.54	$ (0.16)
Diluted net income per share	0.50	$ 0.21	$ 0.30	$ 0.15	$ 0.22	$ 0.13	$ 0.13	$ 0.04	$ 1.17	$ 0.53	$ (0.16)
Convertible senior notes | 2025 Notes
Net income (loss) per share
Dilutive effect of 2025 Notes									0
Convertible senior notes | 2025 Notes | Common Stock
Net income (loss) per share
Conversion price of convertible notes into common stock (in dollars per share)	$ 17.26								$ 17.26			$ 17.26