Schedule (Narrative) (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
SEC Schedule III, Real Estate and Accumulated Depreciation Disclosure [Abstract]
Real estate, federal income tax cost basis	$ 3,662.8	$ 3,340.2
Real estate, federal income tax depreciated basis	$ 2,660.7	$ 2,362.2