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Revolving Credit Facility - Additional Information (Detail) (Unsecured Debt [Member], Revolving Credit Facility [Member], USD $)
In Millions, unless otherwise specified
12 Months Ended
Mar. 31, 2013
Line of Credit Facility [Line Items]  
Unsecured revolving credit facility $ 125
Credit facility maturities date Mar. 20, 2018
Available increase in revolving commitments 100
Borrowings outstanding $ 0
Minimum [Member]
 
Line of Credit Facility [Line Items]  
Unused commitment fee percentage 0.20%
Minimum [Member] | Base Rate [Member]
 
Line of Credit Facility [Line Items]  
Basis spread on variable rate 0.25%
Minimum [Member] | LIBO rate [Member]
 
Line of Credit Facility [Line Items]  
Basis spread on variable rate 1.25%
Maximum [Member]
 
Line of Credit Facility [Line Items]  
Unused commitment fee percentage 0.35%
Maximum [Member] | Base Rate [Member]
 
Line of Credit Facility [Line Items]  
Basis spread on variable rate 1.00%
Maximum [Member] | LIBO rate [Member]
 
Line of Credit Facility [Line Items]  
Basis spread on variable rate 2.00%