Net income per common share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011	Dec. 31, 2010
Computation of basic and diluted earnings per share [Abstract]
Net income from continuing operations	$ 77,489	$ 101,930	$ 256,069	$ 298,555
Weighted average common shares outstanding	191,640,000	187,488,000	190,854,000	186,444,000
Dilutive effect of stock options and RSUs	4,266,000	4,335,000	4,311,000	4,423,000
Dilutive effect of convertible debt	7,385,008	4,431,774	7,521,453	1,477,258
Weighted average common and common equivalent shares outstanding	203,291,000	196,255,000	202,686,000	192,344,000
Basic net income per common share	$ 0.40	$ 0.54	$ 1.34	$ 1.60
Diluted net income per common share - continuing operations	$ 0.38	$ 0.52	$ 1.26	$ 1.55
Weighted average conversion price per share used in calculating dilutive effect of convertible debt (amount per share)	$ 28.36		$ 28.64
Diluted net loss per common share - discontinued operations	$ 0.00	$ (0.01)	$ 0.00	$ (0.03)
Number of antidilutive option shares (in shares)	62,541	134,598	53,374	235,667