Fair Values of Financial Instruments (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Carrying Amount
Financial Assets [Abstract]
Cash and cash equivalents	$ 152,236,000	$ 58,678,000
Mortgage loan	3,481,000	3,502,000
Derivative financial instruments	1,809,000	2,021,000
Financial Liabilities [Abstract]
Mortgage notes payable	1,093,428,000	1,097,493,000
Notes payable to banks	245,000,000	303,000,000
Interest rate swap agreements	8,202,000	8,429,000
Fair Value
Financial Assets [Abstract]
Cash and cash equivalents	152,236,000	58,678,000
Mortgage loan	3,481,000	3,502,000
Derivative financial instruments	1,809,000	2,021,000
Financial Liabilities [Abstract]
Mortgage notes payable	1,058,279,000	1,062,648,000
Notes payable to banks	243,288,000	302,393,000
Interest rate swap agreements	$ 8,202,000	$ 8,429,000