Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Condensed Consolidated Balance Sheets [Abstract]
Allowance for accounts with partners	$ 0.5	$ 0.5
Allowance for value added tax receivable	$ 2.1	$ 6.5
Preferred stock, shares issued	0	0
Preferred stock, shares authorized	500,000	500,000
Preferred stock, par value	$ 25	$ 25
Common stock, par value	$ 0.10	$ 0.10
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	67,092,825	66,443,971
Common stock, shares outstanding	59,538,878	58,862,876
Treasury Stock Shares	7,553,947	7,581,095