Notes Payable and Unsecured Credit Facility (Schedule of Future Principal Payments Due on Debt) (Details) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Six months ending December 31, 2015		$ 6,519
2016		26,450
2017		325,419
2018		150,590
2019		197,685
Thereafter		51,162
Total debt outstanding		757,825	$ 565,909
Principal Payments [Member]
Debt Instrument [Line Items]
Six months ending December 31, 2015		6,519
2016		13,009
2017		12,381
2018		10,277
2019		3,548
Thereafter		2,540
Total debt outstanding		48,274
Balloon Payments [Member]
Debt Instrument [Line Items]
Six months ending December 31, 2015	[1]	0
2016	[1]	13,441
2017	[1]	313,038
2018	[1]	140,313
2019	[1]	194,137
Thereafter	[1]	48,622
Total debt outstanding	[1]	$ 709,551

[1] Includes unsecured credit facility.