Commitments and Contingencies - Unconditional Purchase Obligations (Details) (USD $)	May 31, 2013
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation, Minimum Amount Required	$ 505,000,000
Unrecorded Unconditional Purchase Obligation, Long-Term	600,716,000
Unrecorded Unconditional Purchase Obligation, Long-Term, Due in Next Twelve Months	63,778,000
Unrecorded Unconditional Purchase Obligation, Long-Term, Due Within Two to Three Years	137,051,000
Unrecorded Unconditional Purchase Obligation, Long-Term, Due Within Four to Five Years	122,140,000
Unrecorded Unconditional Purchase Obligation, Long-Term, Due after Five Years	$ 277,747,000