Description of Business - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	2 Months Ended	6 Months Ended		1 Months Ended
	Mar. 23, 2013	Jan. 26, 2013	Apr. 27, 2013	May 31, 2013 Restated Purchase and Sale Agreement	Apr. 22, 2013 Asset Sale Agreement	Apr. 27, 2013 Assets (the "Asset Sale") primarily related to the Intelligent Bandwidth Management Business Asset Sale Agreement	May 31, 2013 Sale Agreement to sell its parcel of undeveloped land located in Tyngsborough, MA to Tyngsborough Commons, LLC ("Tyngsborough Commons") Restated Purchase and Sale Agreement
Sale of facilities and assets, value			$ 18.75	$ 3.50		$ 18.75	$ 3.50
Total dispute amount under asset sale agreement					1.4
Undeveloped Land, expected date to complete sale				Aug. 30, 2013
Undeveloped Land, expected period of extension to complete sale				45 days
Cash distribution per share	$ 1.81
Payment of cash distributions to common stockholders	$ 52.3	$ 361.0