Pension and postretirement benefits - Additional information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Sep. 30, 2014
Pensions And Benefit Restoration Plans [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	$ 51
Defined Benefit Plan Contributions By Employer	13
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	6,200
Defined Benefit Plan Contributions By Employer	$ 1,500