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Shareholders' equity - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions | Mar. 20, 2015 | Jul. 14, 2014 | Dec. 19, 2013 | Mar. 20, 2013 | Mar. 19, 2013
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Equity forward transaction |  |  |  |  |
Public offering related to equity forward transaction (in shares) |  |  |  |  | 6.1
Sale of common stock related to equity forward transaction (in dollars per share) |  |  |  |  | $ 26.75
Closing price of common stock (in dollar per share) |  |  |  |  | $ 27.01
Offering related to underwriters exercising their over-allotment option under equity forward transaction (in shares) |  |  |  | 0.9 |
Shares borrowed by forward counterparty from third party |  |  |  |  | 7.0
Underwriting discount (in dollars per share) |  |  |  |  | $ 1.00312
Forward sale price (in dollars per share) |  |  |  |  | 25.74688
Initial fair value (in dollars per share) |  |  |  |  | $ 0
Delivery of net shares on settlement | 4.7 | 1.0 | 1.3 |  |
Delivery of cash on settlement | $ 104.5 | $ 23.9 | $ 32.1 |  |
Underwriting discount | $ 4.7 | $ 1.0 | $ 1.3 |  |

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- Definition -- None. No documentation exists for this element. -- + References No definition available. + Details
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- Definition Represents the amount of delivery of cash to forward counterparty on settlement of equity forward transaction. + References No definition available. + Details
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- Definition Represents the amount of delivery of net shares to forward counterparty on settlement of equity forward transaction. + References No definition available. + Details
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- Definition Represents the forward sale price determined at the time of entering the equity forward transaction. + References No definition available. + Details
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- Definition Represents the initial fair value of common stock related to equity forward transaction. + References No definition available. + Details
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- Definition Represents the number of shares in connection with public offering under the equity forward transaction. + References No definition available. + Details
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- Definition Represents the number of shares in connection with underwriters exercising their over-allotment option under the equity forward transaction. + References No definition available. + Details
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- Definition Equity Forward Transaction Underwriting Discount, Per Share + References No definition available. + Details
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- Definition Price of a single share of a number of saleable stocks of a company. + References No definition available. + Details
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