Shareholders' equity (Tables)

9 Months Ended

Sep. 30, 2017

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 nine months ended September 30, 2017 and 2016.

Common and Preferred Stock Activity:	Preferred stock		Common stock
(in shares)	Series A convertible		Treasury	Outstanding
Beginning balance as of December 31, 2016	75,625		7,186,521	87,250,897
Conversion of convertible preferred stock	(326	)	—	32,619
Issuance for share-based compensation plans	—		—	43,436
Ending balance as of September 30, 2017	75,299		7,186,521	87,326,952
Beginning balance as of December 31, 2015	76,539		7,186,521	87,038,050
Conversion of convertible preferred stock	(161	)	—	16,109
Issuance for share-based compensation plans	—		—	21,428
Ending balance as of September 30, 2016	76,378		7,186,521	87,075,587