Supplemental Guarantor Condensed Financial Information (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Cash dividend paid	$ 37,400,000	$ 35,600,000	$ 35,300,000
5.75% Senior Notes due 2022
Debt Instrument [Line Items]
Interest rate on senior convertible notes	5.75%
Parent
Debt Instrument [Line Items]
Cash dividend paid	$ 0	$ 0	$ 0
North America | Parent | 5.75% Senior Notes due 2022
Debt Instrument [Line Items]
Debt principal amount	$ 600,000,000
Debt maturity date	Dec. 31, 2022
North America | Parent | Senior Floating Notes Due In 2015
Debt Instrument [Line Items]
Debt maturity date	Dec. 31, 2015