Segment and Related Information - Reconciliation of Operating Income from Segments to Consolidated (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment operating income									$ 101,226	$ 73,723	$ 62,744
Amortization of acquired software									(1,858)	(2,078)	(1,888)
Amortization of customer and trade name intangibles									(6,400)	(6,800)	(6,500)
Other expense, net									(355)	(1,309)	(2,709)
Income before income taxes	24,760	26,698	23,406	19,603	19,062	17,572	15,053	14,132	94,467	65,819	53,868
Segment Reconciling Items [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Amortization of acquired software									(1,858)	(2,078)	(1,888)
Amortization of customer and trade name intangibles									(4,546)	(4,517)	(4,279)
Other expense, net									$ (355)	$ (1,309)	$ (2,709)