Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Mar. 31, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Taxes [Line Items]
Minimum Distribution Percentage of Taxable Income to Qualify for Real Estate Investment Trust				90.00%
Minimum distribution Percentage of Taxable Income to avoid Federal Income Taxes				100.00%
Expected net tax benefit			$ 137,700,000
Income tax (expense) benefit	(2,071,000)	(4,571,000)		(5,490,000)	133,253,000
Percentage of tax position benefit maximum than being realized upon ultimate settlement				50.00%
Liabilities for uncertain tax positions	$ 0			$ 0