Financial instruments and fair value measurement Financial Assets & Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Jun. 30, 2015
Derivatives
Liabilities:
Derivative Liability	$ 15,028	$ 1,970
Derivatives | Quoted Prices In Active Markets (Level 1)
Liabilities:
Derivative Liability	0	0
Derivatives | Significant Other Observable Inputs (Level 2)
Liabilities:
Derivative Liability	15,028	1,970
Derivatives | Significant Unobservable Inputs (Level 3)
Liabilities:
Derivative Liability	0	0
Equity Securities
Assets:
Investments	1,452
Equity Securities | Quoted Prices In Active Markets (Level 1)
Assets:
Investments	1,452
Equity Securities | Significant Other Observable Inputs (Level 2)
Assets:
Investments	0
Equity Securities | Significant Unobservable Inputs (Level 3)
Assets:
Investments	0
Government bonds
Assets:
Investments	25,094	60,512
Government bonds | Quoted Prices In Active Markets (Level 1)
Assets:
Investments	25,094	60,512
Government bonds | Significant Other Observable Inputs (Level 2)
Assets:
Investments	0	0
Government bonds | Significant Unobservable Inputs (Level 3)
Assets:
Investments	0	0
Corporate Bonds
Assets:
Investments	187,946	145,717
Corporate Bonds | Quoted Prices In Active Markets (Level 1)
Assets:
Investments	187,946	145,717
Corporate Bonds | Significant Other Observable Inputs (Level 2)
Assets:
Investments	0	0
Corporate Bonds | Significant Unobservable Inputs (Level 3)
Assets:
Investments	0	0
Asset backed and mortgage backed securities
Assets:
Investments	9,164	10,970
Asset backed and mortgage backed securities | Quoted Prices In Active Markets (Level 1)
Assets:
Investments	0	0
Asset backed and mortgage backed securities | Significant Other Observable Inputs (Level 2)
Assets:
Investments	9,164	10,970
Asset backed and mortgage backed securities | Significant Unobservable Inputs (Level 3)
Assets:
Investments	0	0
Derivatives
Assets:
Derivative Asset	15,231	23,598
Derivatives | Quoted Prices In Active Markets (Level 1)
Assets:
Derivative Asset	0	0
Derivatives | Significant Other Observable Inputs (Level 2)
Assets:
Derivative Asset	15,231	23,598
Derivatives | Significant Unobservable Inputs (Level 3)
Assets:
Derivative Asset	0	0
Fixed income mutual funds
Assets:
Investments	$ 516,889	$ 187,534