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Shareholders' equity (Tables)

6 Months Ended

Jun. 30, 2018

Stockholders' Equity Note [Abstract]

Common and Preferred Stock Activity

The Common and Preferred Stock table below contains additional information about preferred stock conversions during the six months ended June 30, 2018 and 2017.

	Preferred stock			Common stock
Common and Preferred Stock Activity (in shares):	Series A convertible			Treasury			Outstanding
Beginning balance as of December 31, 2017	74,364			7,186,521			87,544,777
Conversion of convertible preferred stock	(241	)		—			24,167
Issuance for share-based compensation plans	—			—			32,147
Ending balance as of June 30, 2018	74,123			7,186,521			87,601,091
Beginning balance as of December 31, 2016	75,625			7,186,521			87,250,897
Conversion of convertible preferred stock	(279	)		—			27,904
Issuance for share-based compensation plans	—			—			37,164
Ending balance as of June 30, 2017	75,346			7,186,521			87,315,965

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

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