Employee Benefits (Details Textual) (USD $)	1 Months Ended	9 Months Ended		12 Months Ended
	Feb. 28, 2013	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2008
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum total number of shares issued		3,898,100
Shares remain available for issuance		705,000
Remaining unrecognized compensation cost		$ 25,000,000
Restricted shares granted to employees vesting period		4 years
Non-employee directors' shares vesting period		1 year
Adjusted pre-tax income	27,000,000
Annual growth rate period	5 years
Compound annual growth	10.00%
Non Recurring Performance Fee				8,700,000
Percentage of deferred share units vesting after two years of service		20.00%
Percentage of deferred share units vesting after three years of service		40.00%
Percentage of deferred share units vesting after four years of service		60.00%
Percentage of deferred share units vesting after five years of service		80.00%
Expense related to mutual fund share incentive awards		8,579,000	7,635,000
Accrued Liability		1,900,000
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Remaining unrecognized compensation cost recognized over a remaining weighted average period		2 years 9 months
Performance Based Restricted Share Grants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted shares granted to employees vesting period		4 years
Deferred Compensation, Share-based Payments
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted shares granted to employees vesting period		6 years
Deferred share units, issued and outstanding		2,710
Weighted average grant date fair value of deferred share units		$ 40.83
Mutual funds
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expense related to mutual fund share incentive awards		$ 1,800,000
Service period of mutual fund share incentive award		2 years
Mutual fund vesting period		1 year
Westwood International Advisors Inc
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted shares granted to employees vesting period		3 years
Purchase of treasury stock, shares		20,251