Long Term Debt (Indebtedness Table) (Details) (USD $) In Thousands, unless otherwise specified		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011 Line of Credit [Member] Twenty Sixteen [Member] Two Point Nine Percent [Member]	Dec. 31, 2012 Line of Credit [Member] Twenty Sixteen [Member] Four Point Three Percent [Member]	Dec. 31, 2012 Unsecured Debt [Member] Twenty Eighteen [Member] Eight Point Eight Seven Five Percent [Member]	Dec. 31, 2011 Unsecured Debt [Member] Twenty Eighteen [Member] Eight Point Eight Seven Five Percent [Member]	Dec. 31, 2011 Unsecured Debt [Member] Twenty Eighteen [Member] Seven Point One Two Five Percent [Member]	Dec. 31, 2012 Unsecured Debt [Member] Twenty Twenty two [Member] Seven Point One Two Five Percent [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 1,036,305	$ 85,000	$ 71,000	$ 715,305	$ 713,409		$ 250,000
Line of Credit Facility, Interest Rate During Period		2.90%	4.30%
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate				8.75%		7.125%
Debt Instrument, Unamortized Discount (Premium), Net	$ (9,695)			$ 9,700	$ 11,600