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Shareholders' equity (Tables)

3 Months Ended

Mar. 31, 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 three months ended March 31, 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	(133	)		—			13,343
Issuance for share-based compensation plans	—			—			17,749
Ending balance as of March 31, 2018	74,231			7,186,521			87,575,869
Beginning balance as of December 31, 2016	75,625			7,186,521			87,250,897
Conversion of convertible preferred stock	(48	)		—			4,795
Issuance for share-based compensation plans	—			—			6,423
Ending balance as of March 31, 2017	75,577			7,186,521			87,262,115

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

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