Comprehensive Income (Details) (USD $)	3 Months Ended		9 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011	Dec. 31, 2010
Comprehensive Income [Abstract]
Comprehensive Income, Net of Tax, Attributable to Parent	$ 76,300,000	$ 101,800,000	$ 251,000,000	$ 293,200,000
Change in unrealized gains and losses on investments, net of tax effect of $97, $1,344, $(332) and $(1,909), respectively.	(1,159,000)	984,000	(5,113,000)	(258,000)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	$ 97,000	$ 1,344,000	$ (332,000)	$ (1,909,000)