Segment and Related Information - Reconciliation of Revenue from Segments to Consolidated (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment operating income									$ 73,723	$ 62,744	$ 50,973
Amortization of acquired software									(2,078)	(1,888)	(1,125)
Amortization of customer and trade name intangibles									(4,517)	(4,279)	(3,331)
Other expense, net									(1,309)	(2,709)	(2,404)
Income before income taxes	19,062	17,572	15,053	14,132	15,035	17,810	11,682	9,341	65,819	53,868	44,113
Operating segments [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment operating income									73,723	62,744	50,973
Segment Reconciling Items [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Amortization of acquired software									(2,078)	(1,888)	(1,125)
Amortization of customer and trade name intangibles									(4,517)	(4,279)	(3,331)
Other expense, net									$ (1,309)	$ (2,709)	$ (2,404)