Long-Term Borrowings (Details Textual) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended							12 Months Ended
	Nov. 30, 2010	Mar. 31, 2012 Period One [Member]	Mar. 31, 2012 Period Two [Member]	Mar. 31, 2012 Period Three [Member]	Mar. 31, 2012 Period Four [Member]	Mar. 31, 2012 Senior Notes due 2018 [Member] Rate	Mar. 31, 2011 Senior Notes due 2018 [Member]	Jun. 30, 2008 Senior Notes due 2018 [Member] Rate	Mar. 31, 2012 Senior notes due 2022 [Member] Rate	Feb. 29, 2012 Senior notes due 2022 [Member] Rate
Debt Instrument [Line Items]
Interest periods for revolving loans under the credit facility		1 month	2 months	3 months	6 months
Issuance of senior notes								$ 300.0		$ 500.0
Net proceeds after original issuance discount and issuance costs								295.6		493.3
Original issuance discount								1.8		2.7
Interest rate on senior unsecured notes								7.25%		4.25%
Redemption options of senior notes						The greater of: (i) 100% of the principal amount of these senior notes to be redeemed, or (ii) the sum of the present values of the remaining scheduled payments of principal and interest discounted at the applicable United States Treasury rate plus 50 basis points, plus accrued and unpaid interest.			The greater of: (i) 100% of the principal amount of these senior notes to be redeemed, or (ii) the sum of the present values of the remaining scheduled payments of principal and interest discounted at the applicable United States Treasury rate plus 35 basis points, plus accrued and unpaid interest.
Percentage of principal amount of senior notes to be redeemed						100.00%			100.00%
Number of basis points to be added to the discounted present value of remaining scheduled payments						50 basis points			35 basis Points
Unamortized discount						1.1	1.3		2.6
Long-Term Borrowings (Textual) [Abstract]
Maximum amount of credit facility	600.0
Expiration date of credit facility	Nov. 30, 2014
Amount of unsecured revolving credit facility	400.0
Provision for swing line loans (maximum)	25.0
Provision for standby letters of credit (maximum)	$ 50.0