Net Income (Loss) Per Share - Numerator and Denominator of Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net income applicable to InterDigital, Inc.	$ 22,251	$ 116	$ 7,743	$ (2,803)	$ 22,367	$ 4,940
Denominator:
Weighted-average shares outstanding: Basic (in shares)	30,757		31,547		30,740	32,076
Dilutive effect of stock options, RSUs, convertible securities and warrants (in shares)	288		229		242	290
Weighted-average shares outstanding: Diluted (in shares)	31,045		31,776		30,982	32,366
Earnings Per Share:
Net income per common share: Basic (in USD per share)	$ 0.72		$ 0.25		$ 0.73	$ 0.15
Dilutive effect of stock options, RSUs, convertible securities and warrants (in USD per share)	0		(0.01)		(0.01)	0
Net income per common share: Diluted (in USD per share)	$ 0.72		$ 0.24		$ 0.72	$ 0.15