Equity - Share Repurchase Program (Details) $ / shares in Units, $ in Millions, $ in Millions					3 Months Ended		6 Months Ended
	Jun. 21, 2018 $ / shares shares	Dec. 29, 2017 shares	Dec. 28, 2017 USD ($) shares	Dec. 15, 2017 shares	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 CAD ($) shares	Jun. 30, 2018 USD ($) shares	Jun. 30, 2017 USD ($)
Stock Repurchase Program
Common share repurchases (in shares)			100,000
Common stock repurchased, value | $			$ 0.2
Maximum number of share that may be repurchased under the new NCIB		11,308,946
Public float amount used to determine share amount, percent		10.00%
Number of shares that may be purchased per day, under the NCIB				11,789
Number of shares repurchased and cancelled							4,300,000	4,300,000
Cost of shares repurchased and cancelled | $								$ 9.2
Dividends per common share (in dollars per share) | $ / shares	$ 4.85
Shares repurchased and cancelled							237,500	237,500
Net income attributable to preferred shares of a subsidiary company | $					$ (1.6)	$ (2.1)		$ 0.1	$ (4.3)
Series 1 Shares
Stock Repurchase Program
Maximum number of share that may be repurchased under the new NCIB				475,000
Public float amount used to determine share amount, percent				10.00%
Preferred shares public float				4,750,000
Series 2 Shares
Stock Repurchase Program
Maximum number of share that may be repurchased under the new NCIB				233,609
Public float amount used to determine share amount, percent				10.00%
Preferred shares public float				2,338,094
Series 3 Shares
Stock Repurchase Program
Maximum number of share that may be repurchased under the new NCIB				164,790
Public float amount used to determine share amount, percent				10.00%
Number of shares that may be purchased per day, under the NCIB	1,000
Preferred shares public float				1,661,906
Shares repurchased and cancelled							123,095	123,095
Preferred share repurchases | $							$ 4.5
Net income attributable to preferred shares of a subsidiary company | $								$ 4.4