Derivative Instruments and Hedging Activities Derivative Instruments Offsetting of derivative assets and liabilities (Details) $ in Thousands	Sep. 30, 2015 USD ($)
Current Assets [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 65,700
Derivative Asset, Fair Value, Gross Liability	0
Derivative Asset	65,700
Noncurrent Assets [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	5,700
Derivative Asset, Fair Value, Gross Liability	(200)
Derivative Asset	5,500
Current Liabilities [Member]
Offsetting Assets [Line Items]
Derivative Liability, Fair Value, Gross Liability	0
Derivative Liability, Fair Value, Gross Asset	0
Derivative Liability	0
Noncurrent Liabilities [Member]
Offsetting Assets [Line Items]
Derivative Liability, Fair Value, Gross Liability	(200)
Derivative Liability, Fair Value, Gross Asset	200
Derivative Liability	$ 0