Fair Values of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Carrying Amount [Member]
Financial Assets [Abstract]
Cash and cash equivalents	$ 30,241	$ 81,856
Derivative financial instruments	2,455	0
Financial Liabilities [Abstract]
Mortgage notes payable	724,090	605,890
Notes payable to banks	313,000	262,000
Interest rate swap agreements	9,501	16,237
Fair Value [Member]
Financial Assets [Abstract]
Cash and cash equivalents	30,241	81,856
Derivative financial instruments	2,455	0
Financial Liabilities [Abstract]
Mortgage notes payable	665,446	623,604
Notes payable to banks	314,834	254,215
Interest rate swap agreements	$ 9,501	$ 16,237