Intangible Assets and Liabilities - Narratives (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Finite-Lived Intangible Assets
Net amortization of intangibles	$ 9.3	$ 12.9
Below and above market rent intangibles
Finite-Lived Intangible Assets
Increase (decrease) in rental income	$ (0.4)	18.8
Assets held for sale | KBR
Finite-Lived Intangible Assets
Accelerated amortization of intangible liabilities		3.3
Assets held for sale | Below-market rent | KBR
Finite-Lived Intangible Assets
Accelerated amortization of intangible liabilities		$ 15.7