Notes Payable and Long-Term Debt - Schedule of Long-Term Debt (Details) - USD ($) $ in Thousands		1 Months Ended
	Jun. 30, 2016	Sep. 30, 2015	Aug. 31, 2020	Aug. 31, 2019
Debt Instrument [Line Items]
Notes payable			$ 1,575,491	$ 2,156,108
Total long-term debt			1,750,947
Debt Issuance Costs, Net			(4,771)	(3,569)
Capital Lease Obligations			31,460	28,239
Long-term Debt, Fair Value			1,791,123
Less current portion			189,287	39,210
Long-term portion			$ 1,601,836	1,749,901
Unsecured debt | Minimum
Debt Instrument [Line Items]
Interest rate			0.00%
Unsecured debt | Maximum
Debt Instrument [Line Items]
Interest rate			10.00%
Committed Term Loans, September 2015 [Member] | Secured debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 600,000
Total long-term debt			236,000
Debt Instrument, Term		10 years
Notes Payable, Other Payables [Member] | Notes Payable, Other Payables [Member] | Revolving credit facility
Debt Instrument [Line Items]
Notes payable			763,215	1,330,550
Private placement, payable in equal installments beginning in 2017 through 2021 | Unsecured debt
Debt Instrument [Line Items]
Total long-term debt			20,000	40,000
Private placement, payable in equal installments beginning in 2017 through 2021 | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 100,000
Interest rate			4.00%
Private placement, payable in its entirety in 2021 | Unsecured debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 160,000
Total long-term debt			$ 162,090	161,978
Interest rate			4.52%
Private placement, payable in its entirety in 2023 | Unsecured debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 130,000
Total long-term debt			$ 137,623	136,086
Interest rate			4.67%
Private placement, payable in 2023 152k [Member] [Member] | Unsecured debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 152,000
Total long-term debt			$ 152,000	152,000
Interest rate			4.39%
Private placement, payable in 2025 80k [Member] | Unsecured debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 80,000
Total long-term debt			$ 80,000	80,000
Interest rate			3.85%
Private placement, payable in 2025 100k [Member] | Unsecured debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 100,000
Total long-term debt			$ 100,000	100,000
Interest rate			3.80%
Private placement, payable in 2025 150k [Member] [Member] | Unsecured debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 150,000
Total long-term debt			$ 154,012	151,776
Interest rate			4.58%
Private placement, payable in its entirety in 2026 | Unsecured debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 80,000
Total long-term debt			$ 80,000	80,000
Interest rate			4.82%
Private placement, payable in its entirety in 2027 [Member] | Unsecured debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 58,000
Total long-term debt			$ 58,000	58,000
Interest rate			4.69%
Private placement, payable in its entirety in 2028 [Member] | Unsecured debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 95,000
Total long-term debt			$ 95,000	95,000
Interest rate			4.74%
Private placement, payable in its entirety in 2031 [Member] | Unsecured debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 100,000
Total long-term debt			$ 100,000	100,000
Interest rate			4.89%
Private placement, payable in its entirety 2033 [Member] | Unsecured debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 100,000
Total long-term debt			$ 100,000	100,000
Interest rate			4.71%
Private placement, payable in its entirety in 2036 [Member] | Unsecured debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 125,000
Total long-term debt			$ 125,000	125,000
Interest rate			5.40%
Private Placement [Member]
Debt Instrument [Line Items]
Total long-term debt			$ 1,363,725	1,379,840
Term loans, 430K payable in 2025 [Member] | Unsecured debt
Debt Instrument [Line Items]
Total long-term debt			366,000	366,000
Bank financing [Member]
Debt Instrument [Line Items]
Total long-term debt			366,000	366,000
Other notes and contracts | Secured debt
Debt Instrument [Line Items]
Total long-term debt			34,709	18,601
Committed Term Loans, September 2016 [Member] | Secured debt
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 600,000
Total long-term debt			$ 130,000
Debt instrument, amount available to be paid and re-advanced	$ 300,000
us-gaap_DebtInstrumentName | us-gaap_LongtermDebtType
Debt Instrument [Line Items]
Long-term Debt, Fair Value				1,789,111
Less current portion				$ 39,210
Unsecured term loans | Unsecured debt
Debt Instrument [Line Items]
Interest rate			2.25%