Share capital (Tables)

6 Months Ended

Jun. 30, 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 six months endedJune 30, 2018 and 2017:

	Six Months Ended June 30,
	2018		2017
Common shares issued, beginning of period	161,994,491		161,279,976
Restricted share awards vested, net of shares withheld	1,015,069		597,021
Restricted share units vested, net of shares withheld	63,702		14,948
Performance shares vested, net of shares withheld	113,627		42,410
Common shares issued, end of period	163,186,889		161,934,355
Treasury shares, end of period	(82,674,941	)	(82,415,774	)
Common shares outstanding, end of period	80,511,948		79,518,581