Non-Controlling Interests, Preferred Shares, Common Shares and Common Shares in Treasury - Preferred Shares Outstanding (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Aug. 30, 2012	Dec. 31, 2011
Class of Stock [Line Items]
Cumulative redeemable preferred shares	$ 405,000		$ 375,000
Class H Preferred Shares [Member]
Class of Stock [Line Items]
Cumulative redeemable preferred shares	205,000		205,000
Class I Preferred Shares [Member]
Class of Stock [Line Items]
Cumulative redeemable preferred shares	0		170,000
Class J Preferred Shares [Member]
Class of Stock [Line Items]
Cumulative redeemable preferred shares	$ 200,000	$ 200,000	$ 0