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Shareholders' equity (Tables)

6 Months Ended

Jun. 30, 2015

Stockholders' Equity Note [Abstract]

Common and Preferred Stock Activity

The Common and Preferred Stock Activity table below contains additional information about preferred stock conversions during the six months ended June 30, 2015 and 2014.

Common and Preferred Stock Activity:	Preferred stock			Common stock
(in shares)	Series A convertible			Treasury		Outstanding
Beginning balance as of December 31, 2014	78,141			4,786,521		89,064,582
Repurchase of common stock	—			2,400,000		(2,400,000	)
Conversion of convertible preferred stock	(1,014	)		—		101,327
Issuance for share-based compensation plans	—			—		135,043
Ending balance as of June 30, 2015	77,127			7,186,521		86,900,952
Beginning balance as of December 31, 2013	79,620			4,786,521		88,710,277
Conversion of convertible preferred stock	(394	)		—		39,455
Issuance for share-based compensation plans	—			—		55,029
Ending balance as of June 30, 2014	79,226			4,786,521		88,804,761

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Tabular disclosure of the change in preferred stock, treasury stock and common stock outstanding.

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