Debt (Schedule of Debt) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Debt [Abstract]
Revolving credit facility - unsecured	$ 167,000	$ 64,000
Bank term loans - unsecured	370,000	120,000
Bank term loans - secured	0	19,250
Fannie Mae term loans - secured (including a premium of $1,756)	80,080	0
Debt, Long-term and Short-term, Combined Amount	$ 617,080	$ 203,250