Fair Values of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Carrying Amount
Financial Assets:
Cash and cash equivalents	$ 127,857	$ 58,678
Mortgage loan receivable	3,438	3,502
Interest rate swap agreements	1,693	2,021
Financial Liabilities:
Mortgage notes payable	1,107,628	1,097,493
Notes payable to banks	350,000	303,000
Interest rate swap agreements	8,721	8,429
Fair Value
Financial Assets:
Cash and cash equivalents	127,857	58,678
Mortgage loan receivable	3,438	3,502
Interest rate swap agreements	1,693	2,021
Financial Liabilities:
Mortgage notes payable	1,093,419	1,062,648
Notes payable to banks	345,272	302,393
Interest rate swap agreements	$ 8,721	$ 8,429