LONG-TERM INCENTIVE COMPENSATION (Details Textual) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) $ / shares shares	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) $ / shares shares	Sep. 30, 2018 CAD ($) shares	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Provision for income taxes	$ 1,783,000	$ 1,620,000	$ 7,236,000		$ 7,013,000
Remaining unrecognized compensation cost recognized over a remaining weighted average period			2 years 2 months	2 years 2 months
Accrued liability	606,000		$ 606,000			$ 1,800,000
Mutual Fund [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Service period of mutual fund share incentive award			3 years	3 years
Expense related to mutual fund share incentive awards	$ 89,000	281,000	$ 274,000		819,000
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	4,848,100		4,848,100
Shares remain available for issuance | shares	409,000		409,000
Remaining unrecognized compensation cost	$ 23,800,000		$ 23,800,000
Nonvested restricted shares | shares	459,008		459,008			519,375
Expense related to mutual fund share incentive awards	$ 3,695,000	$ 4,233,000	$ 11,658,000		$ 12,298,000
Canadian Plan | Westwood International Advisors Inc
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares remain available for issuance | shares	52,064		52,064
Share Based Compensation Arrangement By Share Based Payment Award Available For Grant, Original			$ 7,700,000	$ 10.0
Fund purchases of common stock	$ 46,358		46,358
Purchases of common stock with respect to awards granted			$ 2,700,000	$ 3.5
Share price | $ / shares	$ 51.74		$ 51.74
Amount of shares purchased in the open market	$ 726,000
Purchases of treasury stock, shares | shares			13,031	13,031
Remaining unrecognized compensation cost	$ 800,000		$ 800,000
Remaining unrecognized compensation cost recognized over a remaining weighted average period			1 year 9 months	1 year 9 months
Share-based Compensation Award, First 50% of CEO and CIO Award | Target [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share Pretax Income Goal			$ 20,000,000
Share-based Compensation Award, Second 50% of CEO and CIO Award | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share Pretax Income Goal			$ 32,000,000
Percentage of Pretax income Goal Earned			25.00%	25.00%
Share-based Compensation Award, Second 50% of CEO and CIO Award | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share Pretax Income Goal			$ 44,500,000
Percentage of Pretax income Goal Earned			185.00%	185.00%
Share-based Compensation Award, Second 50% of CEO and CIO Award | Target [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share Pretax Income Goal			$ 36,000,000
Share-based Compensation Award, All Other Performance Grants | Target [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share Pretax Income Goal			$ 20,000,000