18. Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 688	$ 1,711	$ 5,460	$ 3,387	$ 49,203	$ 13,725	$ 6,485	$ 62,093	$ 11,246	$ 131,506
Portfolio operations:
Inventor royalties	192	776	2,623	1,353	11,002	1,181	1,241	21,744	4,944	35,168
Contingent legal fees	4	35	375	177	11,756	2,949	1,037	15,759	591	31,501
Patent acquisition expenses	0	0	0	0	0	0	0	4,000	0	4,000
Litigation and licensing expenses - patents	1,160	987	1,855	3,801	1,689	1,549	2,639	2,989	7,803	8,866
Amortization of patents	857	863	818	656	11,560	4,952	5,278	5,330	3,194	27,120
Other portfolio expenses (income)	1,581	(475)	0	650	400	2,202	0	0	1,756	2,602
Total portfolio expenses	3,794	2,186	5,671	6,637	36,407	12,833	10,195	49,822	18,288	109,257
Net portfolio income (loss)	(3,106)	(475)	(211)	(3,250)	12,796	892	(3,710)	12,271	(7,042)	22,249
General and administrative expenses	4,328	4,630	3,763	3,655	2,754	5,855	6,916	3,301	16,376	18,728
Impairment of patent-related intangible assets	0	0	0	0	0	0	28,210	0	0	28,210
Operating income (loss)	(7,434)	(5,105)	(3,974)	(6,905)	10,042	(4,963)	(38,836)	8,970	(23,418)	(24,689)
Total other income (expense)	5,921	(2,503)	(1,774)	2,821	(21,012)	(27,595)	10,615	(40,890)	4,465	(78,980)
Income (loss) before provision for income taxes	(1,513)	(7,608)	(5,748)	(4,084)	(10,970)	(32,558)	(28,221)	(31,920)	(18,953)	(103,669)
Income tax expense (benefit)	2,147	0	(9)	(314)	(397)	(306)	(285)	(191)	1,824	(1,179)
Net income (loss) including noncontrolling interests in subsidiaries	634	(7,608)	(5,757)	(4,398)	(11,367)	(32,864)	(28,506)	(32,111)	(17,129)	(104,848)
Net (income) loss attributable to noncontrolling interests in subsidiaries	0	0	0	14	(2)	(331)	79	73	14	(181)
Net loss attributable to Acacia Research Corporation	634	(7,608)	(5,757)	(4,384)	(11,369)	(33,195)	(28,427)	(32,038)	(17,115)	(105,029)
Less: Accretion of redeemable preferred stock	(307)	0	0	0	0	0	0	0	(307)	0
Net income (loss) attributable to common shareholders – basic	$ 327	$ (7,608)	$ (5,757)	$ (4,384)	$ (11,369)	$ (33,195)	$ (28,427)	$ (32,038)	$ (17,422)	$ (105,029)
Basic net income (loss) per common share	$ 0.01	$ (0.15)	$ (0.12)	$ (0.09)	$ (0.23)	$ (0.67)	$ (0.57)	$ (0.63)	$ (0.35)	$ (2.10)
Weighted average number of shares outstanding - basic	49,875,750	49,828,361	49,696,016	49,655,881	49,639,172	49,557,748	50,061,812	50,632,958	49,764,002	49,969,062
Add: Accretion of redeemable preferred stock	$ 307	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 307	$ 0
Less: Mark-to-market adjustment for preferred stock embedded derivative	(3,258)	0	0	0	0	0	0	0	(3,258)	0
Net loss attributable to common stockholders - diluted	$ (2,624)	$ (7,608)	$ (5,757)	$ (4,384)	$ (11,369)	$ (33,195)	$ (28,427)	$ (32,038)	$ (20,373)	$ (105,029)
Diluted net loss per share of common stock	$ (0.05)	$ (0.15)	$ (0.12)	$ (0.09)	$ (0.23)	$ (0.67)	$ (0.57)	$ (0.63)	$ (0.40)	$ (2.10)
Weighted average number of shares outstanding - diluted	54,406,835	49,828,361	49,696,016	49,655,881	49,639,172	49,557,748	50,061,812	50,632,958	50,896,773	49,969,062