Notes Payable and Unsecured Credit Facility (Schedule of Future Principal Payments Due on Notes Payable and Unsecured Credit Facility) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2016 USD ($)
Debt Instrument [Line Items]
Six months ending December 31, 2016	$ 19,503
2017	409,060	[1]
2018	149,074
2019	170,180
2020	136,160
Thereafter	50,002
Total	933,979
Revolving Line of Credit [Member]
Debt Instrument [Line Items]
2017	$ 218,000
Credit facility, maturity date	May 28, 2017
Credit facility, available extension period	12 months

[1] Of this amount, $218,000,000 relates to the revolving line of credit under the unsecured credit facility. The maturity date on the revolving line of credit under the unsecured credit facility is May 28, 2017, subject to the Company's right to a 12-month extension.