Capital Stock (Details) - USD ($)	1 Months Ended	6 Months Ended	12 Months Ended
	Jan. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2001
Stock-based compensation disclosure
Compensation expense		$ 8,100,000	$ 11,100,000	$ 21,900,000	$ 15,300,000
Aggregate number of common shares reserved for future issuance			17,700,000
Proceeds from stock options exercised			$ 650,000	$ 5,161,000	4,429,000
Stock options
Stock-based compensation disclosure
Stock options granted to directors (in shares)		3,536,000	1,589,000	3,340,000
Options exercised (in shares)			191,000	555,000
Exercise price (in dollars per share)			$ 2.68
Exercise price (in dollars per share)			$ 6.11
Proceeds from stock options exercised			$ 650,000	$ 5,161,000	$ 4,429,000
Exercisable at the end of the period (in shares)		7,898,000	7,996,000	6,453,000	5,380,000
Weighted-Average Exercise Price (in dollars per share)		$ 13.15	$ 12.16	$ 12.63	$ 11.89
Deferred share units
Stock-based compensation disclosure
Compensation expense		$ 215,000	$ 206,000	$ 380,000	$ 389,000
2001 Director Plan
Stock-based compensation disclosure
Aggregate number of common shares reserved for future issuance						50,000
2001 Director Plan | Deferred share units
Stock-based compensation disclosure
Compensation expense		$ (7,000)	$ 28,000	$ (72,000)	$ 16,000
Stock units issued (in shares)			0
Stock units outstanding (in shares)			6,000
2016 Plan | Stock options
Stock-based compensation disclosure
Options exercised (in shares)			191,000
Compensation Policy for Non-Employee Directors | Stock options
Stock-based compensation disclosure
Stock options granted to directors (in shares)		40,000	80,000	80,000	80,000
Compensation Policy for Non-Employee Directors | Deferred share units
Stock-based compensation disclosure
Compensation expense		$ 215,000	$ 206,000	$ 380,000	$ 389,000
Stock units issued (in shares)	53,248	37,000	47,000	41,000	31,000
Common stock issued when a director ceases to be a member (in shares)			1
Stock units previously granted (in shares)		12,000	12,000	12,000	15,000
Non-employee directors-initial grant | Deferred share units
Stock-based compensation disclosure
Vesting period			3 years
Stock options granted to directors (in shares)			6,500
Non-employee directors-first anniversary | Deferred share units
Stock-based compensation disclosure
Stock options granted to directors (in shares)			3,000
Non-employee directors-after year one | Deferred share units
Stock-based compensation disclosure
Vesting period			1 year
Stock options granted to directors (in shares)			3,000
Annual stock option awards | Stock options
Stock-based compensation disclosure
Vesting period			1 year
Stock options granted to directors (in shares)			10,000
Off-Cycle initial awards | Stock options
Stock-based compensation disclosure
Stock options granted to directors (in shares)			10,000