Capital Stock (Dividends Declared) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended										12 Months Ended
	Jun. 30, 2016	Mar. 31, 2016		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Equity [Abstract]
Dividends declared per common share (in usd per share)	$ 0.09	$ 0.09	[1]	$ 0.09	$ 0.09	$ 0.07	$ 0.07	$ 0.07	$ 0.07	$ 0.05	$ 0.09	$ 0.34	$ 0.26
Total amount	$ 13.3	$ 13.2	[1]	$ 13.5	$ 13.3	$ 10.4	$ 10.1	$ 9.8	$ 9.6	$ 6.9	$ 13.3	$ 50.4	$ 36.4
Cash dividends payable		$ 13.2					$ 10.2				$ 0.0	$ 13.2	$ 10.2

[1] As of March 31, 2016, the Company had $13.2 million of cash dividends payable included in accounts payable and accrued liabilities on the consolidated balance sheet (2017 - none).