Unsecured Exchangeable Senior Notes (Narrative) (Detail) (USD $)	0 Months Ended		1 Months Ended	9 Months Ended
	Feb. 15, 2012	Feb. 16, 2012	Feb. 20, 2012	Sep. 30, 2012	Jan. 10, 2012
Amount paid for repurchase				225,000,000
2.875% Exchangeable Senior Notes [Member]
Coupon/Stated Rate					2.875%
Debt instrument repurchase date by company				Feb. 15, 2012
Put Right expiration date				Feb. 08, 2012
Notes redemption date				Feb. 20, 2012
Debt instrument in connection with redemption last day to exchange notes				Feb. 16, 2012
Debt instrument redemption price percentage of principal		100.00%	100.00%
Amount paid for repurchase	$ 242,735,000		$ 333,459,000