Real Estate Properties (Details) $ in Thousands	1 Months Ended	3 Months Ended
	Jan. 31, 2016 USD ($) ft² property building	Mar. 31, 2016 USD ($) ft² property	Apr. 28, 2016 USD ($) property	Mar. 31, 2016 building	Mar. 31, 2016 item	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Mar. 31, 2015 property building
Real estate properties
Number of properties owned | property		72
Number of buildings				92	92
Total real estate properties, gross						$ 1,767,637	$ 1,696,132
Number of leases entered | property		20
Expansion of area square foot | ft²		25,579
Square Feet | ft²		522,962
Weighted average lease term		11 years 7 months 6 days
Expenditures committed on leases		$ 20,469
Committed but unspent tenant related obligations estimated						22,752
Continuing operations
Real estate properties
Total real estate properties, gross						1,770,983
Discontinued operations
Real estate properties
Number of properties owned | property		1						1
Number of buildings				1	1			1
Real estate properties, net						$ 12,260
Square foot expansion cost		$ 12,800
Sacramento, CA
Real estate properties
Property leased		86.00%
Sacramento, CA | State of California
Real estate properties
Property leased		71.00%
Number of agencies | item					3
Sacramento, CA | Office
Real estate properties
Square Feet | ft²	337,811
Number of Properties Acquired | property	1
Number of Buildings Acquired | building	1
Purchase Price	$ 79,244
Land	4,658
Buildings and Improvement	61,330
Acquired leases	13,525
Acquired Lease obligation	$ (269)
Atlanta, GA
Real estate properties
Number of properties owned | property			1
Land			$ 1,623