Schedule (Narrative) (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation Disclosure [Abstract]
Real estate, federal income tax cost basis	$ 3,302.7	$ 3,174.7
Real estate, federal income tax depreciated basis	$ 2,353.4	$ 2,284.0