Equity (Parenthetical) (Details) - USD ($) $ / shares in Units, $ in Millions		Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Jan. 01, 2017
Class of Stock [Line Items]
Cumulative-effect adjustment	[1]				$ 2.5
Retained Earnings [Member]
Class of Stock [Line Items]
Cumulative-effect adjustment		$ 0.7
Accumulated Other Comprehensive Loss [Member]
Class of Stock [Line Items]
Cumulative-effect adjustment		$ (0.7)
$25 Par Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, par value		$ 25	$ 25	$ 25

[1] The Company recognized a $2.5 million net cumulative-effect adjustment to equity as of January 1, 2017, due to the adoption of ASU 2016-09, Improvements to Employee Share-Based Payment Accounting.