Supplemental Cash Flow Disclosures (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Supplemental Cash Flow Disclosures
Interest paid	$ 30,641	$ 34,489
Taxes paid (recovered)	6	(7)
Interest capitalized		2,786
Non-cash (decrease) increase in working capital related to property, plant and equipment expenditures	(324)	4,606
Non-cash earnings distribution and reinvestment	$ 5,947