Debt - Interest Expense Related to Senior Notes (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Short And Long Term Debt [Line Items]
Coupon rate	$ 580,787	$ 500,019	$ 435,289
Amortization of discount	(36,687)	228	47,136
Amortization of deferred loan costs	16,781	20,476	32,402
Interest expense	507,484	468,072	461,166
Exchangeable Senior Notes [Member]
Short And Long Term Debt [Line Items]
Coupon rate	14,312	24,810	37,562
Amortization of discount	18,425	32,393	48,128
Amortization of deferred loan costs	1,280	2,071	2,691
Interest expense	$ 34,017	$ 59,274	$ 88,381
Effective interest rate	4.60%	4.80%	4.90%