Assets Held for Sale - Summary of Assets Held for Sale (Detail) ft² in Thousands, $ in Thousands	Sep. 30, 2015 USD ($) ft² Property		Dec. 31, 2014 USD ($) ft² Property	Sep. 30, 2014 ft² Property
Long Lived Assets Held For Sale [Line Items]
Number of properties | Property	1,342		1,278	1,494
Square feet	275,000		260,700	301,800
Total assets held for sale | $	$ 369,382	[1]	$ 43,934
Total liabilities associated with assets held for sale – included in Other Liabilities in the Consolidated Balance Sheets | $	$ 7,230
Disposal Group Heldforsale Not Discontinued Operations
Long Lived Assets Held For Sale [Line Items]
Number of properties | Property	19		7
Square feet	5,538		457

[1] Includes two parcels of land held for sale at September 30, 2015