Credit Arrangements - Note Purchase Agreement (Details) (USD $)	3 Months Ended			0 Months Ended
	Mar. 31, 2012	Jun. 30, 2013	Jun. 30, 2012	Jul. 25, 2013 Subsequent Event [Member] Senior Notes [Member] 3.11% Senior Notes due in 2020 [Member]	Jul. 25, 2013 Revolving Credit Facility [Member] Subsequent Event [Member] 2013 Credit Agreement [Member]	May 31, 2013 Treasury Lock [Member] agreement	May 31, 2013 Treasury Lock 1 [Member] Treasury Lock [Member]	May 31, 2013 Treasury Lock 2 [Member] Treasury Lock [Member]	May 31, 2013 Treasury Lock 3 [Member] Treasury Lock [Member]
Debt Instrument [Line Items]
Principal amount of debt				$ 100,000,000.0
Interest rate				3.11%
Proceeds from Issuance of Long-term Debt	107,500,000			100,000,000
Repayments of Long-term Lines of Credit					100,000,000
Prepayment of aggregate principal amount, minimum percent				10.00%
Number of treasury lock agreements						3
Notional Amount		$ 509,947,000	$ 319,326,000				$ 25,000,000	$ 25,000,000	$ 25,000,000