NET INCOME PER SHARE - Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Aug. 07, 2017
Numerator:
Net income attributable to Innoviva stockholders, basic	$ 45,949	$ 39,809	$ 37,740	$ 33,790	$ 263,760	$ 47,089	$ 54,626	$ 29,581	$ 157,288	$ 395,056	$ 134,143
Add: interest expense on 2023 Notes									4,648	5,661	5,647
Net income attributable to Innoviva stockholders, diluted									$ 161,936	$ 400,717	$ 139,790
Denominator:
Weighted-average shares used to compute basic net income per share attributable to Innoviva stockholders									101,150	100,849	106,945
Dilutive effect of 2023 Notes									12,189	12,189	12,189
Dilutive effect of options and awards granted under equity incentive plan and employee stock purchase plan									70	370	732
Weighted-average shares used to compute diluted net income per share attributable to Innoviva stockholders									113,409	113,408	119,866
Net income per share attributable to Innoviva stockholders
Basic net income per share	$ 0.45	$ 0.39	$ 0.37	$ 0.33	$ 2.61	$ 0.47	$ 0.54	$ 0.29	$ 1.55	$ 3.92	$ 1.25
Diluted net income per share	0.42	$ 0.36	$ 0.34	$ 0.31	2.34	$ 0.43	$ 0.49	$ 0.27	$ 1.43	$ 3.53	$ 1.17
Convertible senior notes | 2025 Notes
Net Income Per Share
Dilutive effect of the assumed conversion premium									0	0
Convertible senior notes | 2025 Notes | Common Stock
Net Income Per Share
Conversion price of convertible notes into common stock (in dollars per share)	$ 17.26				$ 17.26				$ 17.26	$ 17.26		$ 17.26