Net Income Per Share - Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net income attributable to Innoviva stockholders, basic	$ 39,809	$ 47,089	$ 111,339	$ 131,296
Add: interest expense on 2023 Notes	1,157	1,413	3,482	4,242
Net income attributable to Innoviva stockholders, diluted	$ 40,966	$ 48,502	$ 114,821	$ 135,538
Denominator:
Weighted-average shares used to compute basic net income per share attributable to Innoviva stockholders	101,191	100,936	101,134	100,806
Dilutive effect of 2023 Notes	12,189	12,189	12,189	12,189
Dilutive effect of options and awards granted under equity incentive plan and employee stock purchase plan	35	238	71	449
Weighted-average shares used to compute diluted net income per share attributable to Innoviva stockholders	113,415	113,363	113,394	113,444
Net income per share attributable to Innoviva stockholders
Basic net income per share	$ 0.39	$ 0.47	$ 1.10	$ 1.30
Diluted net income per share	$ 0.36	$ 0.43	$ 1.01	$ 1.19
Convertible senior notes | 2025 Notes
Net Income Per Share
Dilutive effect of the assumed conversion premium	0	0	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