Stock Compensation - Restricted Stock and Performance Share Grants - Compensation Costs (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	$ 7,605
Stock compensation costs	5,832	5,507	(2,944)
1998 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation costs, expensed	5,054	5,016	(2,944)
Stock compensation costs, capitalized	392	166	0
Stock compensation costs	5,446	5,182	(2,944)
NDSI Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation costs, expensed	$ 386	$ 325	$ 0