Variable Interest Entity - Financial Position of Variable Interest Entity (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 2,540,156	$ 2,492,516	$ 3,037,747	$ 2,435,115
Merchandise inventories	11,800,185	11,918,508
Property and equipment, net	1,896,943	1,892,424
Goodwill	6,697,547	6,664,272
Other long-term assets	272,428	270,942
TOTAL ASSETS	39,267,823	37,669,838
Long-term debt	176,306	177,453
Other long-term liabilities	85,332	110,352
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Cash and cash equivalents	11,768	26,801
Accounts receivables, net	157,307	144,646
Merchandise inventories	172,153	168,931
Prepaid expenses and other	60,395	61,924
Property and equipment, net	33,567	32,667
Goodwill	82,309	82,309
Other intangible assets	79,482	80,974
Other long-term assets	9,111	8,912
TOTAL ASSETS	606,092	607,164
Accounts payable	145,413	150,102
Accrued expenses and other	58,611	37,195
Short-term debt	117,217	115,461
Long-term debt	44,885	39,704
Deferred income taxes	44,265	46,137
Other long-term liabilities	10,915	31,988
Total liabilities	$ 421,306	$ 420,587