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Shareholders' equity (Tables)

12 Months Ended

Dec. 31, 2016

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 2016, 2015 and 2014:

Common and Preferred Stock Activity:	Preferred stock		Common stock
(in shares)	Series A Convertible		Treasury		Outstanding
Balance as of December 31, 2013	79,620		4,786,521		88,710,277
Conversion of convertible preferred stock	(1,479	)	—		147,952
Issuance for share-based compensation plans	—		—		206,353
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	(1,602	)	—		160,162
Issuance for share-based compensation plans	—		—		213,306
Balance as of December 31, 2015	76,539		7,186,521		87,038,050
Conversion of convertible preferred stock	(914	)	—		91,362
Issuance for share-based compensation plans	—		—		121,485
Balance as of December 31, 2016	75,625		7,186,521		87,250,897

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