Commitments and Contingencies - Purchase Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Aug. 31, 2017	Aug. 31, 2016	Aug. 31, 2015
Unrecorded Unconditional Purchase Obligation [Line Items]
Long-term unconditional purchase obligations, period amount purchase	$ 70,500	$ 88,000	$ 66,800
Minimum
Unrecorded Unconditional Purchase Obligation [Line Items]
Long-term unconditional purchase obligations, Total	716,181
Long-term unconditional purchase obligations, Less than 1 Year	54,409
Unrecorded Unconditional Purchase Obligation, Due within Two Years	55,280
Unrecorded Unconditional Purchase Obligation, Due within Three Years	57,367
Unrecorded Unconditional Purchase Obligation, Due within Four Years	57,916
Unrecorded Unconditional Purchase Obligation, Due within Five Years	58,478
Long-term unconditional purchase obligations, More than 5 Years	$ 432,731