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 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, 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 income attributable to InterDigital, Inc.	4,940
Net loss attributable to noncontrolling interest	(2,776)
Net change in unrealized gain (loss) on short-term investments	2,121
Ending balance (in shares) at Jun. 30, 2019		71,260				40,134
Ending balance at Jun. 30, 2019	800,240	$ 712	724,170	1,418,628	(350)	$ (1,354,262)	11,342
Beginning balance (in shares) at Mar. 31, 2019		71,250				39,190
Beginning balance at Mar. 31, 2019	825,513	$ 712	683,615	1,421,884	(1,426)	$ (1,291,979)	12,707
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to InterDigital, Inc.	7,743			7,743
Net loss attributable to noncontrolling interest	(1,365)						(1,365)
Net change in unrealized gain (loss) on short-term investments	1,076				1,076
Dividends declared ($0.35 per share)	(10,895)		104	(10,999)
Issuance of common stock, net (in shares)		10
Issuance of common stock, net	(40)		(40)
Amortization of unearned compensation	2,116		2,116
Repurchase of common stock (in shares)						944
Repurchase of common stock	(62,283)					$ (62,283)
Equity component of debt, net of tax	56,917		56,917
Net convertible note hedge transactions, net of tax	(49,740)		(49,740)
Net warrant transactions	43,416		43,416
Deferred financing costs allocated to equity, net of tax	(1,569)		(1,569)
Reacquisition of equity component of debt due to prepayment, net of tax	(10,649)		(10,649)
Ending balance (in shares) at Jun. 30, 2019		71,260				40,134
Ending balance at Jun. 30, 2019	800,240	$ 712	724,170	1,418,628	(350)	$ (1,354,262)	11,342
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 income attributable to InterDigital, Inc.	116			116
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
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 income attributable to InterDigital, Inc.	22,367
Net loss attributable to noncontrolling interest	(3,437)
Net change in unrealized gain (loss) on short-term investments	444
Ending balance (in shares) at Jun. 30, 2020		71,377				40,573
Ending balance at Jun. 30, 2020	790,706	$ 713	734,565	1,413,382	370	$ (1,379,611)	21,287
Beginning balance (in shares) at Mar. 31, 2020		71,322				40,573
Beginning balance at Mar. 31, 2020	775,596	$ 713	729,541	1,402,048	(42)	$ (1,379,611)	22,947
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to InterDigital, Inc.	22,251			22,251
Net loss attributable to noncontrolling interest	(1,660)						(1,660)
Net change in unrealized gain (loss) on short-term investments	412				412
Dividends declared ($0.35 per share)	(10,781)		136	(10,917)
Exercise of common stock options (in shares)		19
Exercise of common stock options	1,014		1,014
Issuance of common stock, net (in shares)		36
Issuance of common stock, net	(755)		(755)
Amortization of unearned compensation	4,629		4,629
Ending balance (in shares) at Jun. 30, 2020		71,377				40,573
Ending balance at Jun. 30, 2020	$ 790,706	$ 713	$ 734,565	$ 1,413,382	$ 370	$ (1,379,611)	$ 21,287