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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net income attributable to Innoviva stockholders, basic	$ 47,089	$ 23,767	$ 131,296	$ 75,758
Add: interest expense on 2023 Notes	1,413	1,410	4,242	4,231
Net income attributable to Innoviva stockholders, diluted	$ 48,502	$ 25,177	$ 135,538	$ 79,989
Denominator:
Weighted-average shares used to compute basic net income per share attributable to Innoviva stockholders	100,936	106,841	100,806	107,236
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	238	766	449	695
Weighted-average shares used to compute diluted net income per share attributable to Innoviva stockholders	113,363	119,796	113,444	120,120
Net income per share attributable to Innoviva stockholders
Basic net income per share	$ 0.47	$ 0.22	$ 1.30	$ 0.71
Diluted net income per share	$ 0.43	$ 0.21	$ 1.19	$ 0.67
Convertible senior notes | 2025 Notes
Net Income Per Share
Dilutive effect of 2025 Notes	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