Investments - KCG - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Feb. 28, 2017	Dec. 31, 2016	Feb. 29, 2016	Dec. 31, 2015	Nov. 30, 2016
Schedule of Equity Method Investments [Line Items]
Securities borrowed	$ 6,886,436				$ 7,743,562
Securities loaned	$ 2,522,846				$ 2,819,132
KCG Holdings, Inc [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage	24.00%				24.00%
Changes in fair value of investment	$ (4,600)		$ (37,300)
Net income (loss) in earnings		$ 196,200		$ (3,000)
Securities borrowed	2,100				$ 9,200
Securities loaned	$ 2,200				$ 9,200