Share capital (Tables)

3 Months Ended

Mar. 31, 2018

Stockholders' Equity Note [Abstract]

Summary of common shares issued and outstanding

The following table is a summary of the common shares issued and outstanding during the three months endedMarch 31, 2018 and 2017:

	Three Months Ended March 31,
	2018		2017
Common shares issued, beginning of period	161,994,491		161,279,976
Restricted share awards vested, net of shares withheld	7,423		3,440
Restricted share units vested, net of shares withheld	2,055		1,995
Common shares issued, end of period	162,003,969		161,285,411
Treasury shares, end of period	(82,674,941	)	(82,147,821	)
Common shares outstanding, end of period	79,329,028		79,137,590