Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
QUARTERLY FINANCIAL DATA (unaudited) [Abstract]
Revenues	$ 49,203	$ 13,725	$ 6,485	$ 62,093	$ 3,458	$ 36,633	$ 16,457	$ 8,854	$ 131,506	$ 65,402
Inventor royalties	11,002	1,181	1,241	21,744	13	0	4,273	666	35,168	4,952
Contingent legal fees	11,756	2,949	1,037	15,759	646	12,173	3,236	627	31,501	16,682
Patent acquisition expenses	0	0	0	4,000	0	0	0	0	4,000	0
Litigation and licensing expenses - patents	1,689	1,549	2,639	2,989	3,626	4,073	4,134	6,386	8,866	18,219
Amortization of patents	11,560	4,952	5,278	5,330	5,443	5,625	5,571	5,515	27,120	22,154
Marketing, general and administrative expenses (including non-cash stock compensation expense)	(2,778)	(5,855)	(6,916)	(3,301)	140	(12,956)	(7,167)	(7,236)	(18,850)	(27,219)
Impairment of Patent-Related Intangible Assets	0	0	28,210	0	0	2,248	0	0	28,210	2,248
Other	400	2,202	0	0	1,200	0	0	0	2,602	1,200
Total portfolio operations	36,407	12,833	38,405	49,822	10,928	24,119	17,214	13,194
Operating loss	10,018	(4,963)	(38,836)	8,970	(7,330)	(442)	(7,924)	(11,576)	(24,811)	(27,272)
Net portfolio income (loss)	12,796	892	(31,920)	12,271	(7,470)	12,514	(757)	(4,340)	(5,961)	(53)
Total other income (expense)	(20,988)	(27,595)	10,615	(40,890)	(102,950)	159,027	(4,862)	696	(1,629)	1,000
Income (loss) from operations before (provision for) benefit from income taxes	(10,970)	(32,558)	(28,221)	(31,920)	(110,280)	158,585	(12,786)	(10,880)	(103,669)	24,639
(Provision) benefit for income taxes	(397)	(306)	(285)	(191)	(20)	(216)	(1,478)	(1,241)	(1,179)	(2,955)
Net income (loss) including noncontrolling interests in subsidiaries	(11,367)	(32,864)	(28,506)	(32,111)	(110,300)	158,369	(14,264)	(12,121)	(104,848)	21,684
Net (income) loss attributable to noncontrolling interests in subsidiaries	2	331	(79)	(73)	(97)	(96)	(12)	(291)	181	(496)
Net income (loss) attributable to Acacia Research Corporation	$ (11,369)	$ (33,195)	$ (28,427)	$ (32,038)	$ (110,203)	$ 158,465	$ (14,252)	$ (11,830)	$ (105,029)	$ 22,180
Earnings Per Share, Basic and Diluted	$ (0.23)	$ (0.67)	$ (0.57)	$ (0.63)	$ (2.18)	$ 3.13	$ (0.28)	$ (0.24)	$ (2.10)	$ 0.44
Weighted Average Number of Shares Outstanding, Basic and Diluted	49,639,172	49,557,748	50,061,812	50,632,958	50,590,460	50,554,234	50,499,948	50,333,056
Weighted Average Number of Shares Outstanding, Diluted	49,639,172	49,557,748	50,061,812	50,632,958	50,590,460	50,599,974	50,499,948	50,333,056	49,969,062	50,692,012