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						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net income applicable to InterDigital, Inc.	$ 23,784	$ 22,251	$ 116	$ 2,234	$ 7,743	$ (2,803)	$ 46,151	$ 7,174
Denominator:
Weighted-average shares outstanding: basic (in shares)	30,804			31,130			30,762	31,757
Dilutive effect of stock options, RSUs, convertible securities and warrants (in shares)	315			178			267	253
Weighted-average shares outstanding: diluted (in shares)	31,119			31,308			31,029	32,010
Earnings Per Share:
Net income per common share: basic (in USD per share)	$ 0.77			$ 0.07			$ 1.50	$ 0.23
Dilutive effect of stock options, RSUs, convertible securities and warrants (in USD per share)	(0.01)			0			(0.01)	(0.01)
Net income per common share: diluted (in USD per share)	$ 0.76			$ 0.07			$ 1.49	$ 0.22