Segment and Related Information - Reconciliation of Operating Income from Segments to Consolidated (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Segment operating income	$ 43,447	$ 36,945	$ 116,671	$ 95,901
Amortization of acquired software	(5,473)	(5,598)	(16,243)	(16,737)
Amortization of customer and trade name intangibles	(3,492)	(3,458)	(10,413)	(10,273)
Other expense, net	75	(526)	(216)	(1,713)
Income before income taxes	43,522	36,419	116,455	94,188
Operating segments
Segment Reporting Information [Line Items]
Segment operating income	52,412	46,001	143,327	122,911
Segment reconciling items
Segment Reporting Information [Line Items]
Amortization of acquired software	(5,473)	(5,598)	(16,243)	(16,737)
Amortization of customer and trade name intangibles	(3,492)	(3,458)	(10,413)	(10,273)
Other expense, net	$ 75	$ (526)	$ (216)	$ (1,713)