Summary of Debt, Net of Discounts (Detail) (USD $) In Thousands, unless otherwise specified			6 Months Ended		12 Months Ended		6 Months Ended	12 Months Ended							6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Revolving Credit Facilities		Dec. 31, 2011 Revolving Credit Facilities		Jun. 30, 2012 2006 Senior Unsecured Notes	Dec. 31, 2011 2006 Senior Unsecured Notes	Jun. 30, 2012 2011 Senior Unsecured Notes	Dec. 31, 2011 2011 Senior Unsecured Notes	Jun. 30, 2012 2012 Senior Unsecured Notes	Feb. 17, 2012 2012 Senior Unsecured Notes	Jun. 30, 2012 Exchangeable Senior Notes	Dec. 31, 2011 Exchangeable Senior Notes	Jun. 30, 2012 Term Loans	Dec. 31, 2011 Term Loans
Debt Instrument [Line Items]
Principal amount					$ 89,600	[1]	$ 125,000	$ 125,000	$ 450,000	$ 450,000	$ 200,000		$ 11,000	$ 11,000
Unamortized discount													(111)	(180)
Debt instrument, net													10,889	10,820	114,315	14,429
Debt, net	$ 900,204	$ 689,849
Interest rate			Variable	[1]	Variable	[1]	Various	Various							Various
Unsecured senior notes, interest rate									6.875%	6.875%	6.375%	6.375%	9.25%	9.25%		6.20%

[1] Our $42 million collateralized revolving credit facility expired in June 2012.