Income Taxes - Reconciliation Between Cash Dividends Paid and Dividends Paid Deduction (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reconciliation Of Dividends Paid And Deductible Dividends [Line Items]
Dividends paid	$ 153,617	$ 75,253	$ 61,204
Plus: Deemed dividends on convertible debt	7,875	0	0
Less: Dividends designated to prior year	(6,967)	(6,967)	(6,967)
Plus: Dividends designated from the following year	7,030	6,967	6,967
Less: Return of capital	(112,612)	(58,861)	(61,204)
Dividends paid deduction	$ 48,943	$ 16,392	$ 0