Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
U.S. statutory tax rate	21.00%		35.00%
Federal income tax expense	$ 14.5	$ 12.3
Foreign income tax expense (benefit)	$ (1.7)	$ 1.5