Capital Stock (Details) - USD ($)		1 Months Ended					3 Months Ended		9 Months Ended
	Dec. 09, 2016	Jun. 30, 2017	Jan. 31, 2017	Dec. 31, 2016	Nov. 30, 2015	Jun. 30, 2004	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Stock-based compensation disclosure
Stock compensation expense (reduction)							$ 2,600,000	$ 4,400,000	$ 8,300,000	$ 16,000,000
Stock options
Stock-based compensation disclosure
Stock options granted to directors (in shares)									1,533
2001 Director Plan
Stock-based compensation disclosure
Stock compensation expense (reduction)							3,000	(3,000)	$ 36,000	(69,000)
Stock units issued (in shares)						0
Compensation Policy for Non-Employee Directors
Stock-based compensation disclosure
Stock compensation expense (reduction)							$ 61,000	$ 10,800	$ 146,000	$ 323,000
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
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