Deferred Revenue-Right-to-use contracts and Deferred commission expense - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Deferred Revenue Arrangement [Line Items]
Deferred revenue - right-to-use contracts, as of January 1	$ 68,673	$ 62,979
Right-to-use contracts current period, gross	2,923	2,831
Recognition of Deferred Revenue	(1,776)	(1,791)
Deferred Revenue, Period Increase (Decrease)	1,147	1,040
Deferred revenue - right-to-use contracts, as of June 30	69,820	64,019
Deferred commission expense, as of January 1	25,251	22,842
Increase (Decrease) in Deferred Charges	1,239	1,093
Commission expense recognized related to right-to-use contracts	(684)	(630)
Sales And Marketing Deferred Commissions Net	555	463
Deferred commission expense, as of June 30	$ 25,806	$ 23,305
Minimum [Member]
Deferred Revenue Arrangement [Line Items]
Deferred Revenue Estimated Period Of Recognition	1 year
Maximum [Member]
Deferred Revenue Arrangement [Line Items]
Deferred Revenue Estimated Period Of Recognition	31 years