Components of Change in Deferred Revenue-Entry of Right-to-Use Contracts and Deferred Commission Expense (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deferred Revenue Arrangement [Line Items]
Deferred revenue - entry of right-to-use contracts, beginning balance	$ 68,673	$ 62,979
Right To Use Contracts Current Period Gross	13,892	13,815	14,025
Recognition of Deferred Revenue	(8,391)	(8,121)	(7,331)
Net increase in deferred revenue	5,501	5,694
Deferred revenue - entry of right-to-use contracts, ending balance	74,174	68,673	62,979
Deferred commission expense, beginning balance	25,251	22,841
Costs deferred	(6,272)	(5,011)	(5,465)
Deferred commission expense	6,272	5,011
Commission expense recognized	(2,934)	(2,601)	(2,310)
Net increase in deferred commission expense	3,338	2,410
Deferred commission expense, ending balance	$ 28,589	$ 25,251	$ 22,841