Restatement of Previously Issued Consolidated Financial Statements - Narrative (Details) - USD ($)	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
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Other (income) loss	$ 27,015,000	$ 14,622,000	$ 11,364,000	$ 25,014,000	$ 25,407,000	$ 11,952,000	$ 18,083,000	$ 44,509,000	$ 36,378,000	$ 62,592,000	$ 51,000,000	$ 74,544,000	$ 78,015,000	$ 99,951,000	$ 47,609,000
Restatement Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Other (income) loss		$ 0	0	0	$ 743,000	$ 5,000	848,000	7,509,000	$ 0	$ 8,357,000	$ 0	$ 8,361,000		9,105,000	0
Reclassification | Restatement Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
(Gain) loss on investments			(4,100,000)	(2,800,000)			(2,900,000)	7,400,000						(4,600,000)	(9,300,000)
Other (income) loss			$ 4,100	$ 2,800			$ 2,900	$ 7,400						$ 4,600,000	$ 9,300,000