Fair Values of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Carrying Amount
Financial Assets:
Cash and cash equivalents	$ 82,793	$ 58,678
Mortgage loan receivable	3,459	3,502
Interest rate swap agreements	1,043	2,021
Financial Liabilities:
Mortgage notes payable	1,111,386	1,097,493
Notes payable to banks	377,000	303,000
Interest rate swap agreements	11,560	8,429
Fair Value
Financial Assets:
Cash and cash equivalents	82,793	58,678
Mortgage loan receivable	3,459	3,502
Interest rate swap agreements	1,043	2,021
Financial Liabilities:
Mortgage notes payable	1,093,863	1,062,648
Notes payable to banks	377,645	302,393
Interest rate swap agreements	$ 11,560	$ 8,429