Real Estate Properties (Details) $ in Thousands		3 Months Ended	6 Months Ended
	Jul. 06, 2016 USD ($) property	Jun. 30, 2016 USD ($) ft² property building item $ / shares	Jun. 30, 2016 USD ($) ft² property building item $ / shares	Apr. 28, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jun. 30, 2015 property building
Real estate properties
Number of properties | property		72	72
Number of buildings | building		92	92
Total real estate properties, gross		$ 1,776,591	$ 1,776,591		$ 1,696,132
Number of leases entered | property		15	35
Square Feet | ft²		566,640	1,089,602
Square feet expansion | ft²			25,579
Weighted average lease term		10 years 1 month 6 days	10 years 9 months 18 days
Expenditures committed on leases		$ 11,136	$ 31,605
Committed but unspent tenant related obligations estimated		$ 23,891	$ 23,891
Purchase Price	$ 1,623
Continuing operations
Real estate properties
Number of properties | property		72	72
Number of buildings | building		92	92
Total real estate properties, gross		$ 1,779,937	$ 1,779,937
Discontinued operations
Real estate properties
Number of properties | property		1	1			1
Number of buildings | building		1	1			1
Real estate properties, net		$ 12,260	$ 12,260
Square foot expansion cost			$ 12,800
Sacramento, CA
Real estate properties
Number of properties | $ / shares		1	1
Number of buildings | $ / shares		1	1
Square Feet | ft²			337,811
Property leased			86.00%
Purchase Price			$ 79,235
Land		$ 4,688	4,688
Buildings and Improvement		61,722	61,722
Other assumed assets		2,167	2,167
Acquired leases		11,245	11,245
Acquired Lease obligation		$ (587)	$ (587)
Sacramento, CA | State of California
Real estate properties
Property leased			71.00%
Number of agencies | item		3	3
Atlanta, GA
Real estate properties
Number of properties | property	1
Land				$ 1,623