Commitments and Contingencies (Details) ft² in Thousands, $ in Millions	Sep. 30, 2015 USD ($) ft² property
Other Commitments [Line Items]
Rentable square feet of commercial real estate properties (in sq feet)	32,500
Atlanta, GA Building Acquisition (09/2015) [Member]
Other Commitments [Line Items]
Number of office properties acquired | property	2
Kansas City, MO Portfolio Disposition [Member]
Other Commitments [Line Items]
Expected severance costs to be incurred | $	$ 2.5
Kansas City, MO Portfolio Disposition [Member] | Retail Rentable Square Feet [Member]
Other Commitments [Line Items]
Rentable square feet of commercial real estate properties (in sq feet)	804
Kansas City, MO Portfolio Disposition [Member] | Office Rentable Square Feet [Member]
Other Commitments [Line Items]
Rentable square feet of commercial real estate properties (in sq feet)	617