Condensed Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Non-Controlling Interest
Beginning balance (in shares) at Dec. 31, 2018		71,134				37,605
Beginning balance at Dec. 31, 2018	$ 938,013	$ 711	$ 685,512	$ 1,435,970	$ (2,471)	$ (1,182,993)	$ 1,284
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss (income) attributable to InterDigital, Inc.	(2,803)			(2,803)
Proceeds from and increases in noncontrolling interests	12,834						12,834
Net loss attributable to noncontrolling interest	(1,411)						(1,411)
Net change in unrealized gain (loss) on short-term investments	1,045				1,045
Dividends declared ($0.35 per share)	(11,180)		103	(11,283)
Exercise of common stock options	2		2
Issuance of common stock, net (in shares)		116
Issuance of common stock, net	(4,097)	$ 1	(4,098)
Amortization of unearned compensation	2,096		2,096
Repurchase of common stock (in shares)						1,585
Repurchase of common stock	(108,986)					$ (108,986)
Ending balance (in shares) at Mar. 31, 2019		71,250				39,190
Ending balance at Mar. 31, 2019	825,513	$ 712	683,615	1,421,884	(1,426)	$ (1,291,979)	12,707
Beginning balance (in shares) at Dec. 31, 2019		71,268				40,567
Beginning balance at Dec. 31, 2019	786,281	$ 712	727,402	1,412,779	(74)	$ (1,379,262)	24,724
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss (income) attributable to InterDigital, Inc.	116			116
Proceeds from and increases in noncontrolling interests	0
Net loss attributable to noncontrolling interest	(1,777)						(1,777)
Net change in unrealized gain (loss) on short-term investments	32				32
Dividends declared ($0.35 per share)	(10,763)		84	(10,847)
Exercise of common stock options (in shares)		27
Exercise of common stock options	778	$ 1	777
Issuance of common stock, net (in shares)		27
Issuance of common stock, net	(725)		(725)
Amortization of unearned compensation	2,003		2,003
Repurchase of common stock (in shares)						6
Repurchase of common stock	(349)					$ (349)
Ending balance (in shares) at Mar. 31, 2020		71,322				40,573
Ending balance at Mar. 31, 2020	$ 775,596	$ 713	$ 729,541	$ 1,402,048	$ (42)	$ (1,379,611)	$ 22,947