Investments - Summary of Selected Financial Information for KCG (Details) - USD ($) $ in Thousands	3 Months Ended							9 Months Ended
	Aug. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Aug. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Aug. 31, 2017	Aug. 31, 2016	Nov. 30, 2016
Schedule of Equity Method Investments [Line Items]
Securities borrowed	$ 7,758,532							$ 7,758,532		$ 7,743,562
Securities loaned	2,763,253							2,763,253		2,819,132
KCG
Schedule of Equity Method Investments [Line Items]
Net gains from our investment in KCG	$ 2,200			$ 6,100				$ 93,400	$ 24,600
Net earnings (loss)		$ 3,200	$ 196,200		$ 33,600	$ 37,200	$ (3,000)
Securities borrowed										9,200
Securities loaned										$ 9,200