Notes Payable (Details) (USD $)		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2013 Senior Notes Payable Revolving Credit Facility [Member]	Mar. 31, 2012 Senior Notes Payable Revolving Credit Facility [Member]	Sep. 17, 2010 Wells Fargo Non Revolving Line of Credit [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 680,000,000		$ 75,000,000.0
Amount outstanding		400,300,000
Description of variable rate basis		LIBOR
Basis spread on variable rate (in hundredths)		3.00%
Debt instrument interest rate, Minimum (in hundredths)		4.00%
Debt instrument effective interest rate (in hundredths)		4.60%	5.40%
Unused amount available		182,100,000
Additional remaining borrowing capacity		97,600,000
Commitment fee percentage (in hundredths)		0.40%
Expiration date		Nov. 19, 2014
Aggregate annual maturities of notes payable [Abstract]
2014	0
2015	400,250,000
2016	0
2017	0
2018	0
Total long-term debt	$ 400,250,000