Noncontrolling Interests (Redeemable Preferred Units) (Narrative) (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended	1 Months Ended		9 Months Ended										9 Months Ended		1 Months Ended	0 Months Ended	9 Months Ended	1 Months Ended
	Sep. 30, 2012	Aug. 29, 2012 680 Folsom Street [Member]	Sep. 30, 2012 Noncontrolling Interests [Member]	Sep. 30, 2012 Redemption Year Two Thousand Thirteen [Member]	Sep. 30, 2012 Redemption Year Two Thousand Fourteen [Member]	Sep. 30, 2012 Series Two Preferred Units [Member]	Sep. 30, 2012 Series Two Preferred Units [Member] Noncontrolling Interests [Member]	Aug. 15, 2012 Series Two Preferred Units [Member] Noncontrolling Interests [Member]	May 15, 2012 Series Two Preferred Units [Member] Noncontrolling Interests [Member]	Feb. 15, 2012 Series Two Preferred Units [Member] Noncontrolling Interests [Member]	Dec. 31, 2011 Series Two Preferred Units [Member] Noncontrolling Interests [Member]	Dec. 31, 2010 Series Two Preferred Units [Member] Noncontrolling Interests [Member]	Dec. 31, 2009 Series Two Preferred Units [Member] Noncontrolling Interests [Member]	Sep. 30, 2012 OP Units [Member]	Sep. 30, 2012 Series Four Preferred Units [Member]	Aug. 29, 2012 Series Four Preferred Units [Member] 680 Folsom Street [Member]	Aug. 31, 2012 Series Four Preferred Units [Member] Noncontrolling Interests [Member]	Sep. 30, 2012 Series Four Preferred Units [Member] Noncontrolling Interests [Member]	Aug. 29, 2012 Series Four Preferred Units [Member] Noncontrolling Interests [Member] 680 Folsom Street [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Series Two preferred units			995,997				995,997
Liquidation preference percentage							6.00%											2.00%
Preferred units liquidation preference						$ 50.00	$ 50.00								$ 50.00	$ 50.00		$ 50.00
Operating units liquidation preference							$ 38.10
OP Units for each preferred unit						1.312336	1.312336
Maximum redeemable Preferred Units				1,007,662	1,007,662
Dates Series Two Preferred holders can require Operating Partnership to redeem their units for cash				May 14, 2013	May 12, 2014
Series Two Preferred Units redemption price per unit				$ 50.00	$ 50.00
Maximum portion that may be required for redemption of total				0.1666666667	0.1666666667
Number of holders exercising redemption rights							0				0	0	0
Units converted						117,047								153,605
Distributions to Series Two Preferred Units								$ 0.75616	$ 0.73151	$ 0.75616					$ 0.25	$ 0.25
Series Four preferred units			1,221,527															1,221,527
Issuance of redeemable preferred stock		1,588,100																	1,588,100
Redemption of redeemable preferred units, shares																	366,573
Redemption of redeemable preferred units, value	$ 18,329																$ 18,300