GOODWILL AND IDENTIFIABLE INTANGIBLE ASSETS, Schedule of Goodwill (Details) - USD ($)	3 Months Ended			6 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Goodwill [Roll Forward]
Goodwill (beginning of the period)	$ 307,635,000	$ 307,635,000	$ 295,486,000	$ 307,635,000	$ 295,486,000
Foreign currency translation	5,370,000			5,370,000
Impairment losses	0	0	0	0	0
Goodwill (end of the period)	313,005,000	307,635,000	295,486,000	313,005,000	295,486,000
Private client group
Goodwill [Roll Forward]
Goodwill (beginning of the period)	186,733,000	186,733,000	174,584,000	186,733,000	174,584,000
Foreign currency translation	2,622,000			2,622,000
Impairment losses	0		0	0
Goodwill (end of the period)	189,355,000	186,733,000	174,584,000	189,355,000	174,584,000
Capital markets
Goodwill [Roll Forward]
Goodwill (beginning of the period)	120,902,000	120,902,000	120,902,000	120,902,000	120,902,000
Foreign currency translation	2,748,000			2,748,000
Impairment losses	0		0	0
Goodwill (end of the period)	$ 123,650,000	$ 120,902,000	$ 120,902,000	$ 123,650,000	$ 120,902,000