Acquisitions - Additional Information (Detail) - USD ($) $ in Thousands			3 Months Ended												12 Months Ended
	Dec. 31, 2017	Nov. 04, 2015	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	[1]	Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Business Acquisition [Line Items]
Percentage of ownership interest acquired	100.00%		100.00%												100.00%
Additional borrowing															$ 67,000	$ 76,000		$ 298,000
Operating income (loss)			$ 108,037	$ 11,423	$ (38,443)	$ 3,623	$ 120,343		$ (9,353)		$ (26,572)		$ 136,712		$ 84,640	$ 221,130	[1]	$ 127,948
Restricted Share Awards (RSAs) [Member]
Business Acquisition [Line Items]
Issuance of ACI common stock															560,174	148,322		125,026
Awards granted requisite service period															3 years	3 years		3 years
Revolving Credit Facility [Member]
Business Acquisition [Line Items]
Additional borrowing	$ 181,000
PAY.ON [Member]
Business Acquisition [Line Items]
Total purchase price		$ 186,100													$ 186,141
Acquisition related transaction expenses																		$ 900
Revenue																$ 16,500		2,900
Operating income (loss)																$ 17,100		$ 2,100
PAY.ON [Member] | Restricted Share Awards (RSAs) [Member]
Business Acquisition [Line Items]
Issuance of ACI common stock															476,750
Fair value of shares on grant date	$ 11,300		$ 11,300												$ 11,300
Awards granted requisite service period															2 years
PAY.ON [Member] | Restricted Share Awards (RSAs) [Member] | Vest In Every Six Months
Business Acquisition [Line Items]
Percentage of award vesting increment for every six month															25.00%

[1] The Company adopted ASU 2016-09, Compensation - Stock Compensation: Improvements to Employee Share-Based Payment Accounting, ("ASU 2016-09") during the year ended December 31, 2016. The Company elected to early adopt ASU 2016-09 in the third quarter of 2016, which requires it to reflect any adjustments as of January 1, 2016, the beginning of the annual period that includes the interim period of adoption. The impact of the adoption to the Company's previously reported quarterly results for the quarters ended March 31 and June 30, 2016 are reflected in the table above.