Derivative Instruments and Hedging Activities (Details Textual) (Interest rate swap [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Dec. 31, 2011 5-year 1.75% notes [Member]	Dec. 31, 2010 10-year 3.25% notes [Member]	Dec. 31, 2011 10-year 3.125% notes [Member]	Dec. 31, 2010 30-year 5.00% notes [Member]	Jun. 30, 2012 4.55% notes due April 15, 2013 [Member]
Debt Instrument [Line Items]
Financial instruments related to hedges, issuing amount	$ 500,000	$ 700,000	$ 1,000,000	$ 300,000	$ 200,000
Financial instruments related to hedges, interest rate	1.75%	3.25%	3.125%	5.00%	4.55%
Financial instruments related to hedges, maturity period	5 years	10 years	10 years	30 years
Financial instruments related to hedges, maturity date					Apr. 15, 2013