Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Carrying Amount
Financial Assets:
Cash and cash equivalents	$ 80,165	$ 116,241
Mortgage loan receivable	3,353	3,417
Interest rate swap agreements	0	1,131
Financial Liabilities:
Mortgage notes payable	1,193,953	1,339,450
Notes payable to banks	550,000	481,500
Interest rate swap agreements	12,641	11,077
Fair Value
Financial Assets:
Cash and cash equivalents	80,165	116,241
Mortgage loan receivable	3,353	3,417
Interest rate swap agreements	0	1,131
Financial Liabilities:
Mortgage notes payable	1,211,887	1,327,637
Notes payable to banks	553,947	477,967
Interest rate swap agreements	$ 12,641	$ 11,077