Long-Term Debt (Schedule of Long-Term Debt) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010
Maximum borrowing capacity	$ 280,000
Total debt	451,507	456,704	399,537
Less current portion	19,773	24,433	25,493
Total long-term debt	431,734	432,271	374,044
Domestic and Multi-Currency Line of Credit up to $280,000 Due 2015 [Member]
Maximum borrowing capacity	280,000
Total debt	184,256
Debt instrument maturity, year	2015
USD line of credit up to $300,000 due 2012 [Member]
Maximum borrowing capacity	300,000
Total debt		215,025	139,799
Debt instrument maturity, year	2012
6.21% Senior Unsecured Notes Due 2021 [Member]
Total debt	25,000	25,000	25,000
Debt instrument maturity, year	2021
Debt instrument, interest rate	6.21%
6.09% Senior Unsecured Notes Due 2016 [Member]
Total debt	35,000	35,000	35,000
Debt instrument maturity, year	2016
Debt instrument, interest rate	6.09%
6.12% Senior Unsecured Notes Due 2012 [Member]
Total debt	26,667	26,667	40,000
Debt instrument maturity, year	2012
Debt instrument, interest rate	6.12%
7.26% Senior Unsecured Notes Due 2017 [Member]
Total debt	25,000	25,000	25,000
Debt instrument maturity, year	2017
Debt instrument, interest rate	7.26%
Variable Rate Senior Unsecured Note Due 2015 [Member]
Total debt	50,000
Debt instrument maturity, year	2015
Variable Rate Senior Unsecured Note Due 2012 [Member]
Total debt		25,840	31,920
Debt instrument maturity, year	2012
5.25% Convertible Senior Unsecured Notes Due 2029 [Member]
Total debt	$ 105,584	$ 104,172	$ 102,818
Debt instrument maturity, year	2029
Debt instrument, interest rate	5.25%