Capital Stock (Details) - USD ($)		1 Months Ended					2 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Dec. 09, 2016	Jun. 30, 2017	Jan. 31, 2017	Dec. 31, 2016	Nov. 30, 2015	Jun. 30, 2004	Dec. 31, 2015	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Stock-based compensation disclosure
Stock compensation expense (reduction)								$ 3,100,000	$ 4,500,000	$ 5,700,000	$ 11,600,000
Stock options
Stock-based compensation disclosure
Stock options granted to directors (in shares)										1,428
2001 Director Plan
Stock-based compensation disclosure
Stock compensation expense (reduction)								21,000	(35,000)	$ 32,000	(67,000)
Stock units issued (in shares)						0
Compensation Policy for Non-Employee Directors
Stock-based compensation disclosure
Stock compensation expense (reduction)								$ 47,000	$ 10,800	$ 85,000	$ 215,000
Stock options granted to directors (in shares)		80,000
Compensation Policy for Non-Employee Directors | Stock options
Stock-based compensation disclosure
Vesting period							1 year			1 year		1 year
Stock options granted to directors (in shares)				40,000	80,000
Compensation Policy for Non-Employee Directors | Deferred share units
Stock-based compensation disclosure
Stock units issued (in shares)			53,248
Shares issued on annual basis (as a percent)	50.00%
Vesting period	1 year