Summary of Debt (Detail) (USD $) In Thousands, unless otherwise specified			12 Months Ended												12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Revolving Credit Facilities	Dec. 31, 2011 Revolving Credit Facilities	Dec. 31, 2012 2006 Senior Unsecured Notes	Dec. 31, 2011 2006 Senior Unsecured Notes	Dec. 31, 2012 2011 Senior Unsecured Notes	Dec. 31, 2011 2011 Senior Unsecured Notes	Dec. 31, 2012 2012 Senior Unsecured Notes	Feb. 17, 2012 2012 Senior Unsecured Notes	Dec. 31, 2012 Exchangeable Senior Notes	Dec. 31, 2011 Exchangeable Senior Notes	Sep. 30, 2011 Exchangeable Senior Notes	Apr. 30, 2008 Exchangeable Senior Notes	Dec. 31, 2012 Term Loans	Dec. 31, 2011 Term Loans
Debt Instrument [Line Items]
Principal amount			$ 125,000	$ 89,600	$ 125,000	$ 125,000	$ 450,000	$ 450,000	$ 200,000		$ 11,000	$ 11,000			$ 14,200
Unamortized discount											(37)	(180)
Debt instrument, net											10,963	10,820			114,197	14,429
Debt, net	$ 1,025,160	$ 689,849
Unsecured senior notes, interest rate							6.875%	6.875%	6.375%	6.375%	9.25%	9.25%	9.25%	9.25%	6.20%	6.20%
Interest rate			Variable	Variable	Various	Various									Various