Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Taxes [Line Items]
REIT, minimum percentage of taxable income required to be distributed			90.00%
Expected net tax benefit			$ 137,700,000
Income tax (expense) benefit	(4,571,000)	(24,025,000)	133,253,000	(65,634,000)
Percentage of tax position benefit maximum than being realized upon ultimate settlement			50.00%
Liabilities for uncertain tax positions	$ 0		$ 0