Real Estate Assets (Details) ft² in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($) ft²	Mar. 31, 2015 USD ($)
Dispositions [Abstract]
Gains on disposition of discontinued operations	$ 414,496	$ 0
Gains on disposition of property	$ 4,397	$ 1,157
Rentable square feet of building (in sq feet) | ft²	31,200
Division Exit [Member]
Dispositions [Abstract]
Purchase price of real estate	$ 660,000
Gains on disposition of discontinued operations	414,500
Gains on disposition of property	1,300
Disposition closing credits excluded	4,800
Related Party Office Building Disposition [Member]
Dispositions [Abstract]
Purchase price of real estate	4,700
Gains on disposition of property	$ 1,100
Rentable square feet of building (in sq feet) | ft²	32
Buyer occupancy percentage (in hundredths)	79.00%
Disposition closing credits excluded	$ 100
Building Dispositions [Member]
Dispositions [Abstract]
Purchase price of real estate	6,400
Gains on disposition of property	2,000
Disposition closing credits excluded	$ 500