LONG-TERM INCENTIVE COMPENSATION (Details Textual) $ / shares in Units, CAD in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2016 CAD shares	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Amount of shares purchased in the open market			$ 5,629,000		$ 0
Purchases of treasury stock, shares | shares	24,199		117,452	117,452
Remaining unrecognized compensation cost recognized over a remaining weighted average period			2 years 5 months 12 days	2 years 5 months 12 days
Accrued liability	$ 1,400,000		$ 1,400,000			$ 2,000,000
Mutual Fund [Member]
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	$ 313,000	$ 149,000	$ 933,000		879,000
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
Shares remain available for issuance | shares	346,000		346,000
Remaining unrecognized compensation cost	$ 27,300,000		$ 27,300,000
Nonvested restricted shares | shares	647,556		647,556			580,469
Expense related to mutual fund share incentive awards	$ 4,082,000	$ 4,865,000	$ 12,164,000		$ 12,560,000
Canadian Plan | Westwood International Advisors Inc
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares remain available for issuance | shares	85,494		85,494
Share Based Compensation Arrangement By Share Based Payment Award Available For Grant, Original			$ 7,600,000	CAD 10.0
Fund purchases of common stock	$ 43,648		43,648
Purchases of common stock with respect to awards granted			$ 4,500,000	CAD 6.0
Share price | $ / shares	$ 53.11		$ 53.11
Amount of shares purchased in the open market			$ 600,000
Purchases of treasury stock, shares | shares			10,474	10,474
Remaining unrecognized compensation cost	$ 1,000,000		$ 1,000,000
Remaining unrecognized compensation cost recognized over a remaining weighted average period			1 year 7 months 13 days	1 year 7 months 13 days
Performance​ Based​ Restricted​ Shares​ For Future Performance Years
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Nonvested restricted shares | shares	51,258		51,258