Summary of Significant Accounting Policies Earnings per share (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
Accounting Policies [Abstract]
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
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic									0	33
Net Loss Available to Common Stockholders, Basic and Diluted									$ (105,029)	$ 22,147
Weighted Average Number of Shares Outstanding, Basic									49,969,062	50,495,119
Weighted Average Number Diluted Shares Outstanding Adjustment									0	196,893
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
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
Anti-dilutive equity-based incentive awards excluded from the computation of diluted income (loss) per share									3,129,719	4,425,187