Net income per common share (Details) (USD $) In Thousands, except Share data	3 Months Ended	12 Months Ended
Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2011	Mar. 31, 2010	Mar. 31, 2009
Computation of basic and diluted earnings per share [Abstract]
Net income from continuing operations	$ 130,612	$ 101,930	$ 104,748	$ 91,877	$ 429,167	$ 217,005	$ 245,587
Net income					$ 418,950	$ 217,005	$ 245,587
Weighted average common shares outstanding					187,066,000	183,642,000	183,158,000
Dilutive effect of stock options and RSUs					4,463,000	3,697,000	3,336,000
Dilutive effect of convertible debt					3,185,591		294,445
Weighted average common and common equivalent shares outstanding					194,715,000	187,339,000	186,788,000
Basic net income per common share					$ 2.24	$ 1.18	$ 1.34
Diluted net income per common share - continuing operations	$ 0.65	$ 0.52	$ 0.55	$ 0.48	$ 2.20	$ 1.16	$ 1.31
Number of antidilutive option shares (in shares)					132,084	4,109,841	3,685,806
Weighted average conversion price per share used in calculating dilutive effect of convertible debt (amount per share)					$ 29.61
Diluted net loss per common share - discontinued operations	$ (0.03)	$ (0.01)	$ (0.01)	$ (0.01)	$ (0.05)	$ 0.00	$ 0.00

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Assumption that stock options or restrictive stock units were exercised for computing the dilutive effect of convertible securities.

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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) in the future that were not included in the computation of diluted EPS because to do so would increase EPS amounts or decrease loss per share amounts for the period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 13, 14

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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 171

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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-Paragraph 40
-Subparagraph c

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The amount of net income or loss for the period per each share of common stock outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 21
-Article 9

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 36, 37, 38

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 20
-Article 5

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 18
-Article 7

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This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses and taxes from ongoing operations before extraordinary items, cumulative effects of changes in accounting principles, and noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 95
-Paragraph 28

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 51
-Paragraph 29

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The amount of income (loss) from continuing operations available to each share of common stock outstanding during the reporting period and each share that would have been outstanding assuming the issuance of common shares for all dilutive potential common shares outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 21
-Article 9

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 40
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-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
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-Paragraph 20
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-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 18
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The amount of income (loss) from discontinued operations, net of related tax effect, per each diluted share of common stock outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 5
-Section E
-Paragraph Question 3

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Debt securities outstanding shall be assumed to have been converted at the beginning of the period (or at time of issuance, if later), and the resulting common shares shall be included in common shares used to calculate diluted earnings per shares. The dilutive effect of convertible debt securities shall be reflected in diluted Earnings Per Share by application of the if-converted method.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 26, 27, 28

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The portion of consolidated profit or loss for the period, net of income taxes, which is attributable to the parent. If the entity does not present consolidated financial statements, the amount of profit or loss for the period, net of income taxes.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 19
-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 51
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-Number 210
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-Number 87-21

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-Name Statement of Financial Accounting Standard (FAS)
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The average number of shares issued and outstanding that are used in calculating diluted EPS, determined based on the timing of issuance of shares in the period.

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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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Number of [basic] shares, after adjustment for contingently issuable shares and other shares not deemed outstanding, determined by relating the portion of time within a reporting period that common shares have been outstanding to the total time in that period.

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