Selected Quarterly Results (unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Effect of Fourth Quarter Events [Line Items]
Revenues	$ 102,161	$ 72,523	$ 75,609	$ 68,631	$ 75,326	$ 75,079	$ 69,555	$ 87,444	$ 318,924	$ 307,404	$ 532,938
Net income applicable to InterDigital, Inc.'s common shareholders	$ 13,754	$ 2,234	$ 7,743	$ (2,803)	$ 2,083	$ 21,752	$ 10,966	$ 30,230	$ 20,928	$ 65,031	$ 176,220
Net income per share — basic (in usd per share)	$ 0.44	$ 0.07	$ 0.25	$ (0.09)	$ 0.06	$ 0.63	$ 0.32	$ 0.87	$ 0.66	$ 1.89	$ 5.09
Net income per share — diluted (in usd per share)	$ 0.44	$ 0.07	$ 0.24	$ (0.09)	$ 0.06	$ 0.61	$ 0.31	$ 0.85	$ 0.66	$ 1.84	$ 4.93
Non-Current Patent Royalties
Effect of Fourth Quarter Events [Line Items]
Revenues									$ 19,782	$ 26,329
As Reported
Effect of Fourth Quarter Events [Line Items]
Net income applicable to InterDigital, Inc.'s common shareholders					$ 1,830					$ 63,868	$ 174,293
Net income per share — basic (in usd per share)					$ 0.05					$ 1.85	$ 5.04
Net income per share — diluted (in usd per share)					$ 0.05					$ 1.81	$ 4.87