Note Pension and postretirement benefits - Additional information (Detail) $ in Thousands	3 Months Ended
	Jun. 30, 2016 USD ($)
Other Pension Plans Defined Benefit Member
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plans Estimated Future Employer Contributions In Current Fiscal Year	$ 45,200
Defined Benefit Plan Contributions By Employer	43
Other Postretirement Benefit Plans Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plans Estimated Future Employer Contributions In Current Fiscal Year	6,400
Defined Benefit Plan Contributions By Employer	$ 1,800