Segment Information - Selected Financial Data (Details) - USD ($) $ 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	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues									$ 1,258,294	$ 1,009,780	$ 1,024,191
Depreciation and amortization									(122,569)	(97,350)	(102,224)
Stock-based compensation expense									(36,763)	(20,360)	(13,683)
Corporate and unallocated expenses									(104,718)	(92,296)	(144,715)
Interest, net									(52,066)	(30,388)	(38,449)
Other, net	$ 3,399	$ (2,369)	$ 1,402	$ (1,912)	$ (688)	$ (1,304)	$ (1,677)	$ (55)	520	(3,724)	(2,619)
Income before income taxes	$ 90,652	$ 36,950	$ (16,806)	$ (38,586)	$ 108,744	$ 17,245	$ (10,810)	$ (23,380)	72,210	91,799	43,572
Operating Segments | ACI On Premise
Segment Reporting Information [Line Items]
Revenues									579,334	576,755	598,590
Segment Adjusted EBITDA									321,305	323,902	347,094
Depreciation and amortization									(11,992)	(11,634)	(13,094)
Stock-based compensation expense									(7,651)	(4,348)	(2,234)
Operating Segments | ACI On Demand
Segment Reporting Information [Line Items]
Revenues									678,960	433,025	425,601
Segment Adjusted EBITDA									66,501	12,015	(1,832)
Depreciation and amortization									(34,395)	(31,541)	(34,171)
Stock-based compensation expense									(7,995)	(4,338)	(2,230)
Corporate and other
Segment Reporting Information [Line Items]
Depreciation and amortization									(76,182)	(54,175)	(54,959)
Stock-based compensation expense									$ (21,117)	$ (11,674)	$ (9,219)