LONG-TERM INCENTIVE COMPENSATION (Details Textual)	1 Months Ended		3 Months Ended		6 Months Ended
	Feb. 28, 2015 USD ($)	Feb. 28, 2014	Jun. 30, 2015 USD ($) $ / shares shares	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) $ / shares shares	Jun. 30, 2015 CAD shares	Jun. 30, 2014 USD ($)	Jun. 30, 2015 CAD shares	Dec. 31, 2014 USD ($) shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Amount of shares purchased in the open market					$ 1,327,000		$ 0
Accrued liability			$ 1,500,000		$ 1,500,000				$ 844,000
Mutual Fund
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Mutual fund vesting period					1 year	1 year
Service period of mutual fund share incentive award					2 years	2 years
Expense related to mutual fund share incentive awards			$ 317,000	$ 185,000	$ 730,000		310,000
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total number of shares that may be issued under the stock based compensation Plan (including predecessor plans to the Plan) | shares			4,398,100		4,398,100			4,398,100
Shares remain available for issuance | shares			685,000		685,000			685,000
Remaining unrecognized compensation cost			$ 31,600,000		$ 31,600,000
Remaining unrecognized compensation cost recognized over a remaining weighted average period					2 years 7 months 6 days	2 years 7 months 6 days
Restricted shares granted to employees vesting period		5 years
Nonvested restricted shares | shares			573,856		573,856			573,856	496,457
Expense related to mutual fund share incentive awards			$ 4,017,000	$ 2,989,000	$ 7,695,000		$ 6,468,000
Canadian Plan | Westwood International Advisors Inc
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares remain available for issuance | shares			91,000		91,000			91,000
Fund purchases of common stock			$ 8,000,000.0		$ 8,000,000.0			CAD 10,000,000
Purchases of common stock with respect to awards granted					$ 5,500,000	CAD 6,800,000
Share price | $ / shares			$ 59.57		$ 59.57
Number of shares purchased in the open market | shares					21,818	21,818
Amount of shares purchased in the open market					$ 1,300,000
Purchase of treasury stock, shares | shares					53,545	53,545
Remaining unrecognized compensation cost			$ 1,200,000		$ 1,200,000
Remaining unrecognized compensation cost recognized over a remaining weighted average period					2 years 22 days	2 years 22 days
Performance Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Adjusted pre-tax income	$ 46,000,000.0
Compound annual growth rate	5 years
Compound annual growth	10.00%
Performance​ Based​ Restricted​ Shares​ For Future Performance Years
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Nonvested restricted shares | shares			118,939		118,939			118,939