Non-Controlling Interests, Preferred Shares, Common Shares and Common Shares in Treasury - Preferred Shares Outstanding (Parenthetical) (Detail) (USD $)	12 Months Ended		1 Months Ended	12 Months Ended		1 Months Ended	12 Months Ended
	Dec. 31, 2012 Class H Preferred Shares [Member]	Dec. 31, 2011 Class H Preferred Shares [Member]	Aug. 30, 2012 Class I Preferred Shares [Member]	Dec. 31, 2011 Class I Preferred Shares [Member]	Dec. 31, 2012 Class I Preferred Shares [Member]	Aug. 30, 2012 Class J Preferred Shares [Member]	Dec. 31, 2012 Class J Preferred Shares [Member]	Dec. 31, 2011 Class J Preferred Shares [Member]
Class of Stock [Line Items]
Preferred stock dividend rate	7.375%	7.375%	7.50%	7.50%		6.50%	6.50%
Cumulative redeemable preferred shares liquidation value	$ 500	$ 500		$ 500		$ 500	$ 500
Cumulative redeemable preferred shares authorized	750,000	750,000		750,000	750,000		750,000	750,000
Cumulative redeemable preferred shares issued and outstanding	410,000	410,000		340,000			400,000