Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
QUARTERLY FINANCIAL DATA (unaudited) [Abstract]
Revenues	$ 3,458	$ 36,633	$ 16,457	$ 8,854	$ 21,969	$ 64,658	$ 41,351	$ 24,721
Inventor royalties	13	0	4,273	666	3,313	17,844	0	1,573	$ 4,952	$ 22,730	$ 18,462
Contingent legal fees	646	12,173	3,236	627	4,238	7,709	10,418	4,109	16,682	26,474	16,169
Litigation and licensing expenses - patents	3,626	4,073	4,134	6,386	5,463	7,348	7,324	7,723	18,219	27,858	39,373
Amortization of patents	5,443	5,625	5,571	5,515	6,222	6,467	10,759	10,760	22,154	34,208	53,067
Marketing, general and administrative expenses (including non-cash stock compensation expense)	335	(12,715)	(6,734)	(6,916)	(9,056)	(8,334)	(7,535)	(7,994)	(26,030)	(32,919)	(38,176)
Other expenses - business development	195	241	433	320	557	666	1,334	522	1,189	3,079	3,391
Impairment of Patent-Related Intangible Assets	0	2,248	0	0	2,175	0	40,165	0	2,248	42,340	74,731
Impairment of Goodwill									0	0	30,149
Other	1,200	0	0	0	0	0	(1,242)	1,742	1,200	500	4,141
Total operating costs and expenses	10,788	37,075	24,381	20,430	31,024	48,368	76,293	34,423	92,674	190,108	277,659
Operating loss	(7,330)	(442)	(7,924)	(11,576)	(9,055)	16,290	(34,942)	(9,702)	(27,272)	(37,409)	(152,622)
Total other income (expense)	(102,950)	159,027	(4,862)	696	592	261	(52)	(3)	51,911	798	(56)
Income (loss) from operations before (provision for) benefit from income taxes	(110,280)	158,585	(12,786)	(10,880)	(8,463)	16,551	(34,994)	(9,705)	24,639	(36,611)	(152,678)
(Provision) benefit for income taxes	(20)	(216)	(1,478)	(1,241)	(2,414)	(9,655)	(5,927)	(192)	(2,955)	(18,188)	(4,800)
Net income (loss) including noncontrolling interests in subsidiaries	(110,300)	158,369	(14,264)	(12,121)	(10,877)	6,896	(40,921)	(9,897)	21,684	(54,799)	(157,478)
Net (income) loss attributable to noncontrolling interests in subsidiaries	(97)	(96)	(12)	(291)	(266)	(186)	(348)	68	(496)	(732)	2,558
Net income (loss) attributable to Acacia Research Corporation	$ (110,203)	$ 158,465	$ (14,252)	$ (11,830)	$ (10,611)	$ 7,082	$ (40,573)	$ (9,965)	$ 22,180	$ (54,067)	$ (160,036)
Earnings Per Share, Basic and Diluted	$ (2.18)	$ 3.13	$ (0.28)	$ (0.24)	$ (0.21)	$ 0.14	$ (0.81)	$ (0.20)	$ 0.44	$ (1.08)	$ (3.25)
Weighted Average Number of Shares Outstanding, Basic and Diluted	50,590,460	50,554,234	50,499,948	50,333,056	50,237,784	50,124,302	50,015,869	49,925,550
Weighted Average Number of Shares Outstanding, Diluted	50,590,460	50,599,974	50,499,948	50,333,056	50,237,784	50,618,757	50,015,869	49,925,550	50,692,012	50,075,847	49,505,817