Derivative Instruments (Narrative) (Details) (USD $)	0 Months Ended		1 Months Ended	12 Months Ended					1 Months Ended		0 Months Ended
	Sep. 29, 2011	Apr. 15, 2010	Dec. 31, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Jul. 12, 2011	May 31, 2011	Dec. 31, 2011 4.2% Senior Notes, Due December 2021 [Member] years	Dec. 09, 2011 4.2% Senior Notes, Due December 2021 [Member]	Apr. 15, 2010 4.5 % Senior Notes [Member] years	Dec. 31, 2011 4.5 % Senior Notes [Member]	Dec. 06, 2010 4.5 % Senior Notes [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate contract with notional amount	$ 350,000,000	$ 300,000,000					$ 350,000,000
Stated interest rate									4.20%	4.20%	4.50%	4.50%	4.50%
Interest rate contract settlement	34,700,000	31,000,000	38,700,000
Interest rate contract settlement term									10		10
Interest rate contract settlement, interest rate, effective percentage									5.30%		5.80%
Additional interest rate contract settlement			4,000,000
Recognized as other expense			800,000
Interest expense			37,900,000	29,332,000	16,150,000	17,178,000
Notional amount foreign currency exchange contracts								500,000
Accumulated other comprehensive income loss from shareholders' equity			$ 7,600,000	$ 7,600,000