Real Estate Transactions (Details) ft² in Thousands, $ in Millions	Jun. 15, 2017 USD ($) ft²	Oct. 25, 2017 ft² property
Discontinued Operations, Disposed of by Sale | The ACS Center
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of property (in sq ft) | ft²	996
Gross sales price of property sold | $	$ 166.0
Gain from sale of business | $	$ 119.8
Discontinued Operations, Held-for-sale | Properties in Orlando, Florida | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of property (in sq ft) | ft²		1,038
Number of properties | property		3