Net income per common share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Jun. 30, 2013	Jun. 30, 2012
Earnings Per Share [Abstract]
Net income	$ 78,579	$ 78,710
Weighted Average Number of Shares Outstanding, Basic	196,950,000	193,452,000
Dilutive effect of stock options and RSUs	3,672,000	3,546,000
Dilutive effect of convertible debt	11,644,236	6,702,184
Weighted average common and common equivalent shares outstanding	212,266,000	203,700,000
Earnings Per Share, Basic	$ 0.40	$ 0.41
Earnings Per Share, Diluted	$ 0.37	$ 0.39
Weighted average conversion price per share used in calculating dilutive effect of convertible debt (amount per share)	$ 26.66	$ 27.79
Number of antidilutive option shares (in shares)	50,198	110,125

The weighted average price per share of the conversion feature embedded in the debt instrument.

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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