Segment and Related Information - Reconciliation of Operating Income from Segments to Consolidated (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment operating income	$ 160,930	$ 131,305	$ 108,043
Amortization of acquired software	(21,686)	(22,235)	(4,440)
Amortization of customer and trade name intangibles	(36,000)	(36,400)	(10,300)
Other income (expense), net	698	(1,998)	381
Income before income taxes	161,628	129,307	108,424
Operating segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment operating income	196,528	167,271	118,388
Segment Reconciling Items
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Amortization of acquired software	(21,686)	(22,235)	(4,440)
Amortization of customer and trade name intangibles	(13,912)	(13,731)	(5,905)
Other income (expense), net	$ 698	$ (1,998)	$ 381