Change In Preferred Stock (Detail) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
5.75% Cumulative Convertible Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding beginning balance	1,497	1,500
5.75% Cumulative Convertible Preferred Stock (Series A)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding beginning balance	1,100	1,100
4.50% Cumulative Convertible Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding beginning balance	2,559	2,559
5.00% Cumulative Convertible Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares outstanding beginning balance	2,096	2,096