Share capital (Tables)

12 Months Ended

Dec. 31, 2016

Stockholders' Equity Note [Abstract]

Summary of preferred shares issued and outstanding

The following table is a summary of the Preferred shares issued and outstanding:

	Preferred Shares
Preferred shares issued and outstanding, beginning of year	—
Preferred shares issued	6,000
Preferred shares issued and outstanding, end of year	6,000

Summary of common shares issued and outstanding

The following table is a summary of the common shares issued and outstanding during the years ended December 31, 2016, 2015 and 2014:

	Years Ended December 31,
	2016		2015		2014
Common shares issued, beginning of year	160,570,772		155,554,224		154,488,497
Restricted share awards vested, net of shares withheld	612,100		614,945		615,659
Restricted share units vested, net of shares withheld	18,486		13,260		10,265
Options exercised	30,530		782,465		412,656
Warrants exercised	—		3,593,715		—
Direct issuance of common stock	—		639		1,380
Performance shares vested, net of shares withheld	48,088		11,524		25,767
Common shares issued, end of year	161,279,976		160,570,772		155,554,224
Treasury shares, end of year	(82,147,724	)	(77,670,155	)	(71,684,379	)
Common shares outstanding, end of year	79,132,252		82,900,617		83,869,845