Debt (Details) (USD $)	6 Months Ended
	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011
Debt [Abstract]
Long-term debt	$ 125,600,000		$ 0
Credit facility, maximum borrowing capacity		200,000,000	150,000,000
Credit facility, permitted increase in maximum borrowing capacity		100,000,000	150,000,000
Credit facility, expiration date	November 1, 2012
Amount borrowed under the amended credit facility	129,500,000
Restriction on maximum additional borrowing outside amended credit facility	250,000,000
Weighted average interest rate (in hundredths)	1.80%
Interest and fees related to the credit facility	$ 788,000