Restatement of Previously Issued Consolidated Financial Statements - Summary of Impacts of the Restatement Adjustments on Previously Reported Consolidated Capital Reserves and Total Equities (Details) - USD ($) $ in Thousands	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	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	Aug. 31, 2015
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Capital reserves	$ 1,482,003	$ 1,559,040	$ 1,450,326	$ 1,324,372	$ 1,267,808	$ 1,397,834	$ 1,560,498	$ 1,592,434	$ 1,450,326	$ 1,560,498	$ 1,559,040	$ 1,397,834	$ 1,482,003	$ 1,267,808		$ 1,485,433
Stockholders' equity	8,165,028	7,920,836	7,866,357	7,742,948	7,705,640	7,680,371	7,808,580	7,819,516	7,866,357	7,808,580	7,920,836	7,680,371	8,165,028	7,705,640	$ 7,759,159	7,551,439
Income (loss) before income taxes	248,332	236,839	(21,729)	207,788	(109,088)	(238,612)	18,302	219,232	186,059	237,534	422,898	(1,078)	671,230	(110,166)	402,125
Net income (loss)	$ 240,545	181,620	165,959	187,182	(74,327)	(72,488)	14,617	203,156	353,141	217,773	534,761	145,285	$ 775,306	70,958	383,026
As Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Capital reserves		1,803,078	1,646,837	1,520,218	1,471,217	1,577,469	1,713,784	1,691,603	1,646,837	1,713,784	1,803,078	1,577,469		1,471,217		1,604,670
Stockholders' equity		8,162,533	8,061,960	7,937,775	7,905,825	7,858,956	7,961,594	7,931,280	8,061,960	7,961,594	8,162,533	7,858,956		7,905,825	7,866,250	7,669,411
Income (loss) before income taxes		289,484	(14,550)	199,555	(94,845)	(209,158)	23,597	225,554	185,005	249,151	474,490	39,994		(54,852)	419,878
Net income (loss)		229,146	166,626	179,619	(50,552)	(46,140)	14,973	208,942	346,245	223,915	575,391	177,775		127,223	423,969
Restatement Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Capital reserves		(244,038)	(196,511)	(195,846)	(203,409)	(179,635)	(153,286)	(99,169)	(196,511)	(153,286)	(244,038)	(179,635)		(203,409)		(119,237)
Stockholders' equity		(241,697)	(195,603)	(194,827)	(200,185)	(178,585)	(153,014)	(111,764)	(195,603)	(153,014)	(241,697)	(178,585)		(200,185)	(107,091)	$ (117,972)
Income (loss) before income taxes		(52,645)	(7,179)	8,233	(14,243)	(29,454)	(5,295)	(6,322)	1,054	(11,617)	(51,592)	(41,072)		(55,314)	(17,753)
Net income (loss)		$ (47,526)	$ (667)	$ 7,563	$ (23,775)	$ (26,348)	$ (356)	$ (5,786)	$ 6,896	$ (6,142)	$ (40,630)	$ (32,490)		$ (56,265)	$ (40,943)