Condensed Consolidated Financial Statements - Summary of Changes in the Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill, gross amount prior to period		$ 957,123
Goodwill, total impairment prior to period		(47,432)
Goodwill [Roll Forward]
Goodwill, beginning of period	$ 909,691
Goodwill from acquisitions	369,781
Goodwill, end of period	1,279,472
ACI On Demand
Goodwill [Line Items]
Goodwill, gross amount prior to period		183,783
Goodwill, total impairment prior to period		0
Goodwill [Roll Forward]
Goodwill, beginning of period	183,783
Goodwill from acquisitions	369,781
Goodwill, end of period	553,564
ACI On Premise
Goodwill [Line Items]
Goodwill, gross amount prior to period		773,340
Goodwill, total impairment prior to period		$ (47,432)
Goodwill [Roll Forward]
Goodwill, beginning of period	725,908
Goodwill from acquisitions	0
Goodwill, end of period	$ 725,908