Notes Payable and Long-Term Debt - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Aug. 31, 2018	May 31, 2018	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2017	May 31, 2017	Feb. 28, 2017	Nov. 30, 2016	Feb. 28, 2018	Feb. 28, 2017	May 31, 2018	May 31, 2017	Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2016
Debt Instrument [Line Items]
Interest expense		$ 18,984	$ 49,340	$ 40,176	$ 40,702	$ 53,828	$ 39,201	$ 39,945	$ 38,265	$ 80,878	$ 78,210	$ 130,218	$ 117,411	$ 149,202	$ 171,239	$ 113,704
Long-term Debt, Fair Value		1,800,000												1,800,000
Notes payable		2,272,196	$ 2,868,506	$ 3,071,639	$ 2,480,264	1,985,163	$ 3,321,808	$ 3,867,438	$ 3,227,564	$ 3,071,639	$ 3,867,438	$ 2,868,506	$ 3,321,808	2,272,196	1,985,163
Long-term Debt		$ 1,918,689												1,918,689
Capitalized Interest														(6,700)	(6,900)	$ (30,300)
Long-term debt repaid														$ 208,000
Unsecured debt | Minimum
Debt Instrument [Line Items]
Interest rate		1.30%												1.30%
Unsecured debt | Maximum
Debt Instrument [Line Items]
Interest rate		15.25%												15.25%
Five-year revolving facilities | Line of credit | Revolving credit facility
Debt Instrument [Line Items]
Line of credit facility, amount outstanding		$ 0				480,000								$ 0	480,000
Debt Instrument, Term														5 years
Five-year revolving facilities | Line of credit | Revolving credit facility | Minimum
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate														0.00%
Five-year revolving facilities | Line of credit | Revolving credit facility | Maximum
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate														1.45%
Three-year revolving facility | Line of credit | Revolving credit facility
Debt Instrument [Line Items]
Debt Instrument, Term														3 years
Uncommitted lines of credit | Line of credit | Revolving credit facility
Debt Instrument [Line Items]
Long-term Line of Credit, Noncurrent		454,100												$ 454,100
Other international subsidiaries, lines of credit | Line of credit | Revolving credit facility
Debt Instrument [Line Items]
Line of credit facility, amount outstanding		279,400												279,400
Line Of Credit, Collateralized Amount		40,500												40,500
Miscellaneous short-term notes payable | Line of credit | Revolving credit facility
Debt Instrument [Line Items]
Line of credit facility, amount outstanding		7,400												7,400
Master participation agreements | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Short-term bank loans and notes payable current borrowing capacity		36,000												36,000
Notes payable		$ 6,300												$ 6,300
Master participation agreements | Notes Payable, Other Payables [Member] | Minimum
Debt Instrument [Line Items]
Interest rate		2.22%												2.22%
Master participation agreements | Notes Payable, Other Payables [Member] | Maximum
Debt Instrument [Line Items]
Interest rate		3.72%												3.72%
Term loans from cooperative and other banks | Line of credit | Revolving credit facility
Debt Instrument [Line Items]
Interest rate		5.59%												5.59%
Long-term Debt		$ 0				15,000								$ 0	15,000
Private placement, payable in equal installments beginning in 2014 through 2018 | Unsecured debt
Debt Instrument [Line Items]
Interest rate		6.18%												6.18%
Debt Instrument, Face Amount		$ 400,000												$ 400,000
Long-term Debt		$ 0				80,000								$ 0	80,000
Private placement, payable in installments through 2018 | Unsecured debt
Debt Instrument [Line Items]
Interest rate		5.60%												5.60%
Debt Instrument, Face Amount		$ 60,000												$ 60,000
Long-term Debt		0				4,615								0	4,615
Private placement, payable in equal installments beginning in 2014 through 2018 | Unsecured debt
Debt Instrument [Line Items]
Long-term Debt		$ 0				10,000								$ 0	10,000
Private placement, payable in equal installments beginning in 2014 through 2018 | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Interest rate		5.78%												5.78%
Debt Instrument, Face Amount		$ 50,000												$ 50,000
Private placement, payable in equal installments beginning in 2017 through 2021 | Unsecured debt
Debt Instrument [Line Items]
Long-term Debt		$ 60,000				80,000								$ 60,000	80,000
Private placement, payable in equal installments beginning in 2017 through 2021 | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Interest rate		4.00%												4.00%
Debt Instrument, Face Amount		$ 100,000												$ 100,000
Other notes and contracts | Secured debt
Debt Instrument [Line Items]
Long-term Debt		32,607				62,652								32,607	62,652
Notes Payable, Other Payables [Member] | Notes Payable, Other Payables [Member] | Revolving credit facility
Debt Instrument [Line Items]
Notes payable		1,437,264				$ 1,695,423								1,437,264	$ 1,695,423
Recourse loan commitments | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Short-term bank loans and notes payable current borrowing capacity		180,900												180,900
Notes payable		$ 98,300												$ 98,300
Interest rate		3.22%												3.22%
Short-Term Notes Payable, Surplus Funds Program [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Notes payable		$ 69,300												$ 69,300
Short-Term Notes Payable, Surplus Funds Program [Member] | Notes Payable, Other Payables [Member] | Minimum
Debt Instrument [Line Items]
Interest rate		0.10%												0.10%
Short-Term Notes Payable, Surplus Funds Program [Member] | Notes Payable, Other Payables [Member] | Maximum
Debt Instrument [Line Items]
Interest rate		1.40%												1.40%
Committed Term Loans, September 2015 [Member] | Secured debt
Debt Instrument [Line Items]
Debt Instrument, Term	10 years
Debt Instrument, Face Amount		$ 600,000												$ 600,000
Long-term Debt		$ 236,000												$ 236,000