SCHEDULE III-Consolidated Real Estate and Accumulated Depreciation (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Real Estate and Accumulated Depreciation [Line Items]
Balance, beginning of period	$ 1,687,276		$ 1,165,097		$ 968,332
Property acquisitions	270,082		563,858		188,971
Improvements	41,303	[1]	13,595	[1]	8,383	[1]
Cost of Real Estate Sold	(57,188)		(37,599)
Other	(2,797)	[1],[2]	(17,675)	[1],[2]	(589)	[1],[2]
Balance, end of period	1,938,676		1,687,276		1,165,097
Balance, beginning of period	234,595		221,997		194,124
Additions-depreciation	47,792	[1]	42,498	[1]	28,462	[1]
Cost of Real Estate Sold	(9,216)		(12,225)
Other	(2,677)	[1],[2]	(17,675)	[1],[2]	(589)	[1],[2]
Balance, end of period	$ 270,494		$ 234,595		$ 221,997

[1] Includes discontinued operations for 160 King Street, which was sold on December 4, 2012 and Valencia Corporate Center, which was sold on August 30, 2011.

[2] Other deductions for the years ended December 31, 2012, 2011 and 2010 represent the write-off of fully depreciated assets