Stock Based Compensation and Stock Options (Details 1) (USD $)	3 Months Ended		6 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Stock compensation expense for time based options and performance based options
Cost of revenues	$ 82,622,000	$ 78,940,000	$ 164,047,000	$ 155,704,000
General and administrative	11,981,000	12,592,000	24,155,000	24,886,000
Total cost of stock-based compensation included in income before income tax provision	10,855,000	13,020,000	21,862,000	26,270,000
Amount of income tax benefit recognized	4,225,000	5,139,000	8,636,000	10,191,000
Effect on diluted net income per share	$ 0.58	$ 0.68	$ 1.16	$ 1.37
Time Based Options [Member] | Performance Shares [Member]
Stock compensation expense for time based options and performance based options
Cost of revenues	115,000	125,000	228,000	250,000
General and administrative	(26,000)	546,000	159,000	1,079,000
Total cost of stock-based compensation included in income before income tax provision	89,000	671,000	387,000	1,329,000
Amount of income tax benefit recognized	(35,000)	(262,000)	(150,000)	(520,000)
Amount charged against net income	$ 54,000	$ 409,000	$ 237,000	$ 809,000
Effect on diluted net income per share	$ 0.00	$ (0.04)	$ (0.02)	$ (0.07)