SUPPLEMENTARY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SUPPLEMENTARY FINANCIAL DATA (UNAUDITED)
Net revenue	$ 79,858	$ 61,680	$ 67,086	$ 52,380	$ 69,520	$ 48,643	$ 58,562	$ 40,492	$ 261,004	$ 217,217	$ 133,569
Total operating expenses	2,638	4,019	4,411	11,685	(3,111)	(8,621)	(10,732)	(11,149)	(22,753)	(33,613)	(24,581)
Income from operations	77,220	57,661	62,675	40,695	66,409	40,022	47,830	29,343	238,251	183,604	108,988
Income tax benefit (expense), net	196,073	0	0	0	(4)	0	0	0	196,073	(4)	(95)
Net income	269,215	50,167	56,616	30,330	58,514	23,767	35,146	16,845	406,328	134,272	59,536
Net income attributable to noncontrolling interest	5,455	3,078	1,990	749	129	0	0	0	11,272	129	0
Net income attributable to the Innoviva stockholders	$ 263,760	$ 47,089	$ 54,626	$ 29,581	$ 58,385	$ 23,767	$ 35,146	$ 16,845	$ 395,056	$ 134,143	$ 59,536
Basic net income per share	$ 2.61	$ 0.47	$ 0.54	$ 0.29	$ 0.55	$ 0.22	$ 0.33	$ 0.16	$ 3.92	$ 1.25	$ 0.54
Diluted net income per share	$ 2.34	$ 0.43	$ 0.49	$ 0.27	$ 0.50	$ 0.21	$ 0.30	$ 0.15	$ 3.53	$ 1.17	$ 0.53