Subsequent Event (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Mar. 31, 2012	Apr. 19, 2012
Subsequent Event [Line Items]
Revolving credit agreement initiation date	Apr. 19, 2012
Borrowing limit under the unsecured revolving credit facility		$ 100
Basis spread on variable interest rate		0.50%
Covenant terms, debt coverage ratio		1.75
Covenant terms, interest coverage ratio		3.50
Standby Letters Of Credit [Member]
Subsequent Event [Line Items]
Borrowing limit under the unsecured revolving credit facility		$ 15