Investments - Summary of Selected Financial Information for KCG (Details) - USD ($) $ in Thousands	3 Months Ended						6 Months Ended
	May 31, 2017	Mar. 31, 2017	Dec. 31, 2016	May 31, 2016	Mar. 31, 2016	Dec. 31, 2015	May 31, 2017	May 31, 2016	Nov. 30, 2016
Schedule of Equity Method Investments [Line Items]
Securities borrowed	$ 7,900,395						$ 7,900,395		$ 7,743,562
Securities loaned	3,446,853						3,446,853		2,819,132
KCG Holdings, Inc [Member]
Schedule of Equity Method Investments [Line Items]
Net gains from our investment in KCG	95,800			$ 55,800			91,200	$ 18,500
Net earnings (loss)		$ 3,200	$ 196,200		$ 37,200	$ (3,000)
Securities borrowed	3,100						3,100		9,200
Securities loaned	$ 1,000						$ 1,000		$ 9,200