Debt (Debt Outstanding) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Secured Debt	$ 279,474	$ 376,278
Senior Notes	250,000	0
Unsecured Debt	150,000	150,000
Long-term Debt	812,974	716,778
Weighted average interest rate	3.80%	3.70%
Fixed Rate Debt [Member]
Debt Instrument [Line Items]
Secured Debt	271,374	376,278
Secured Debt Weighted Average Interest Rate	4.90%	5.40%
Long-term Debt	521,374	376,278
Weighted average interest rate	4.70%	5.40%
Fixed Rate Debt Unsecured Notes [Member] [Domain]
Debt Instrument [Line Items]
Senior Notes	250,000	0
Unsecured Debt Weighted Average Interest Rate	4.40%	0.00%
Fixed Rate Debt Hedged [Member]
Debt Instrument [Line Items]
Unsecured Debt Weighted Average Interest Rate	3.00%
Weighted average interest rate	3.00%
Variable Rate Debt Hedged [Member]
Debt Instrument [Line Items]
Unsecured Debt		125,000
Unsecured Debt Weighted Average Interest Rate		1.90%
Long-term Debt		125,000
Weighted average interest rate		1.90%
Variable Rate Debt Unhedged [Member]
Debt Instrument [Line Items]
Secured Debt	8,100	0
Secured Debt Weighted Average Interest Rate	1.50%	0.00%
Long-term Debt	166,600	215,500
Weighted average interest rate	1.50%	1.70%
Variable Rate Debt Unhedged Revolver [Member] [Member]
Debt Instrument [Line Items]
Unsecured Debt	133,500	190,500
Unsecured Debt Weighted Average Interest Rate	1.50%	1.70%
Variable Rate Debt Unhedged Term Loan [Member] [Domain]
Debt Instrument [Line Items]
Unsecured Debt	$ 25,000	$ 25,000
Unsecured Debt Weighted Average Interest Rate	1.90%	1.90%