Acquisitions - Purchase Price of PAY.ON (Detail) - PAY.ON [Member] - USD ($) $ in Thousands		12 Months Ended
	Nov. 04, 2015	Dec. 31, 2017
Business Acquisition [Line Items]
Cash payments to PAY.ON shareholders		$ 180,994
Issuance of ACI common stock		5,379
Working capital adjustment		(232)
Total purchase price	$ 186,100	$ 186,141