Senior Unsecured Notes Repurchases (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Unsecured Senior Notes [Line Items]
Principal amount repurchased	$ 91,578
Purchase Price	93,960
2014 Notes [Member]
Unsecured Senior Notes [Line Items]
Principal amount repurchased	9,000
Purchase Price	9,439
2017 Notes [Member]
Unsecured Senior Notes [Line Items]
Principal amount repurchased	4,223
Purchase Price	4,632
2028 Notes [Member]
Unsecured Senior Notes [Line Items]
Principal amount repurchased	55,955
Purchase Price	57,041
2032 Notes [Member]
Unsecured Senior Notes [Line Items]
Principal amount repurchased	22,400
Purchase Price	$ 22,848