Transactions with Related Parties - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Related Party Transaction [Line Items]
Lease payments	$ 1.4	$ 0.9	$ 1.0
Percentage of ownership interests in Previleged Access	91.60%	91.80%
Lease agreement, term	The leases entered into between the customer and us for the rental of a Site are generally month-to-month or for a period of one to ten years, renewable upon the consent of the parties or, in some instances, as provided by statute.
Chief Executive Officer [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party	$ 0.3