Share-based payments (Tables)

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Statement [Line Items]

Disclosure of number and weighted average exercise prices of share options [Table Text Block]

	Year ended				Year ended
	Dec. 31, 2017				Dec. 31, 2016
	Number			Weighted	Number			Weighted
	of shares			average	of shares			average
	subject			exercise	subject			exercise
	to option			price	to option			price
				C$				C$
Balance, beginning of year	1,470,377		$	19.24	1,904,185		$	17.57
Forfeited	(20,002	)		15.86	(125,677	)		17.52
Expired	(927,023	)		21.22	(308,131	)		9.70
Balance, end of year	523,352		$	15.86	1,470,377		$	19.24

Disclosure of range of exercise prices of outstanding share options [Table Text Block]

Dec. 31, 2017
		Weighted-		Weighted-			Weighted-
		average		average	Number of		average
Range of	Number of	remaining		exercise	options		exercise
exercise prices	options	contractual life		price	exercisable		price
C$	outstanding	(years)		C$			C$
$15.86	523,352	0.2	$	15.86	523,352	$	15.86

Dec. 31, 2016
		Weighted-
		average		Weighted-	Number of		Weighted-
Range of exercise	Number of	remaining		average	options		average
prices	options	contractual life		exercise price	exercisable		exercise price
C$	outstanding	(years)		C$			C$
$15.86 - 18.33	543,354	1.2	$	15.86	543,354	$	15.86
18.34 - 21.28	757,023	0.2		20.80	757,023		20.80
21.29 - 21.98	10,000	0.1		21.75	10,000		21.75
21.99 - 22.97	60,000	0.9		22.20	60,000		22.20
22.98 - 23.74	100,000	0.6		23.74	100,000		23.74
$15.86 - 23.74	1,470,377	0.6	$	19.24	1,470,377	$	19.24

Deferred Share Unit [Member]

Statement [Line Items]

Disclosure of number and weighted average exercise prices of other equity instruments [Table Text Block]

		Year ended
		Dec. 31, 2017		Dec. 31, 2016
Granted during the year:
Number of units		130,964		231,867
Weighted average price (C$/unit)	$	8.59	$	5.81
Expenses recognized during the year 1 (notes 5c, 18)	$	2,982	$	2,111
Payments made during the year (note 18)	$	638	$	1,078

Restricted Share Unit [Member]

Statement [Line Items]

Disclosure of number and weighted average exercise prices of other equity instruments [Table Text Block]

		Year ended
		Dec. 31, 2017			Dec. 31, 2016
Number of units, beginning of year		3,492,408			1,943,507
Number of units granted during the year		987,194			2,576,957
Credits for dividends		8,156			14,776
Number of units forfeited during the year		(201,946	)		(133,329	)
Number of units vested 1		(880,099	)		(909,503	)
Number of units, end of year		3,405,713			3,492,408
Weighted average price - granted (C$/unit)	$	10.60		$	4.01
Expenses recognized during the year 2 (note 5c)	$	12,937		$	7,776
Payments made during the year (note 18)	$	5,491		$	2,736