Net Income Per Share (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
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to InterDigital, Inc.	$ 13,754	$ 2,234	$ 7,743	$ (2,803)	$ 2,083	$ 21,752	$ 10,966	$ 30,230	$ 20,928	$ 65,031	$ 176,220
Weighted-average shares outstanding: basic (in shares)									31,546	34,491	34,605
Dilutive effect of stock options, RSUs and convertible securities (in shares)									239	816	1,174
Weighted-average shares outstanding: diluted (in shares)									31,785	35,307	35,779
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
Dilutive effect of stock options, RSUs and convertible securities									0	(0.05)	(0.16)
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
Antidilutive securities excluded from computation of earnings per share amount (in shares)									11,118	4,429	19
Restricted stock units and stock options
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Antidilutive securities excluded from computation of earnings per share amount (in shares)									128	25	19
Convertible securities
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Antidilutive securities excluded from computation of earnings per share amount (in shares)									5,495	0	0
Warrants
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Antidilutive securities excluded from computation of earnings per share amount (in shares)									5,495	4,404	0