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SHARE-BASED COMPENSATION PLANS (Details) - USD ($)
$ / shares in Units, $ in Millions
 1 Months Ended 12 Months Ended
Jan. 23, 2017
Jan. 22, 2016
Jan. 23, 2015
Jun. 30, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share Options                
Assumptions used for estimating the fair value of share options using the Black-Scholes option-pricing model                
Risk-free interest rate (as a percent)         2.20% 1.80% 1.50%  
Expected dividend yield (as a percent)         3.50% 2.70% 2.60%  
Volatility (as a percent)         33.00% 33.00% 33.00%  
Weighted average expected life of the options         6 years 6 years 6 years  
Weighted average grant date fair value of options granted per share (in dollars per share)         $ 6.12 $ 7.61 $ 6.23  
Share options, additional general disclosures                
Compensation expense recognized (in dollars)         $ 1.5 $ 1.3 $ 1.0  
Aggregate grant date fair value of share based awards issued (in dollars)         1.8      
Unrecognized compensation cost         $ 1.8      
Unrecognized compensation cost recorded, period         3 years      
Number of Shares Under Option                
Balance at the beginning of the period (in shares)         1,939,690 2,421,944 3,692,301  
Options granted (in shares)         289,104 213,008 202,485  
Options canceled (in shares)             (18,230)  
Options exercised (in shares)         (395,621) (695,262) (1,454,612)  
Balance at the end of the period (in shares)         1,833,173 1,939,690 2,421,944 3,692,301
Vested or expected to vest at the end of the period (in shares)         1,833,173      
Exercisable at the end of the period (in shares)         1,337,280      
Weighted Average Exercise Price                
Balance at the beginning of the period (in dollars per share)         $ 12.94 $ 13.07 $ 11.76  
Options granted (in dollars per share)         26.30 30.32 25.00  
Options canceled (in dollars per share)             19.75  
Options exercised (in dollars per share)         5.98 18.69 11.31  
Balance at the end of the period (in dollars per share)         16.55 $ 12.94 $ 13.07 $ 11.76
Exercisable at the end of the period (in dollars per share)         12.58      
Vested or expected to vest at the end of the period (in dollars per share)         $ 16.55      
Weighted Average Remaining Contractual Term                
Balance at the end of the period         5 years 3 months 4 days 4 years 10 months 6 days 4 years 29 days 4 years 1 month 28 days
Options granted         9 years 26 days 9 years 26 days 9 years 29 days  
Options exercised         1 year 1 month 21 days 3 months 15 days 2 years 4 months 17 days  
Vested or expected to vest at the end of the period         5 years 3 months 4 days      
Exercisable at the end of the period         4 years 15 days      
Aggregate intrinsic value                
Options, vested or expected to vest and exercisable (in dollars)         $ 35.3      
Options exercised (in dollars)         $ 8.8      
Share Options | Minimum                
Share options, additional general disclosures                
Vesting period         3 years      
Restricted Shares                
Share options, additional general disclosures                
Compensation expense recognized (in dollars)         $ 4.1 $ 3.6 $ 2.7  
Aggregate grant date fair value of share based awards issued (in dollars)         4.7 $ 5.2    
Unrecognized compensation cost         $ 5.2      
Unrecognized compensation cost recorded, period         5 years      
Number of Non-Vested Restricted Shares                
Non-vested at the beginning of the period (in shares)         323,022      
Granted (in shares)         165,709 155,000    
Vested (in shares)         (130,500)      
Forfeited (in shares)         (5,769)      
Non-vested at the end of the period (in shares)         352,462 323,022    
Restricted Shares | Minimum                
Share options, additional general disclosures                
Vesting period         3 years      
Restricted Shares | Maximum                
Share options, additional general disclosures                
Vesting period         5 years      
Restricted share units                
Share options, additional general disclosures                
Aggregate grant date fair value of share based awards issued (in dollars) $ 1.8 $ 1.6 $ 1.3          
Number of Non-Vested Restricted Shares                
Granted (in shares) 52,426 37,008 35,614          
Restricted share, additional disclosure                
Period for calculation of total return to shareholders 3 years 3 years 3 years          
2007 Plan                
SHARE-BASED COMPENSATION PLANS                
Additional shares authorized       4,500,000        
Shares reserved for future issuance       991,117        
Shares available for future awards         4,936,124      
Maximum term of options         10 years      
2007 Plan | Maximum                
SHARE-BASED COMPENSATION PLANS                
Maximum number of awards that may be granted to an individual per calendar year (in shares)         1,000,000      
2007 Plan | Maximum | Non Employee Trustee                
SHARE-BASED COMPENSATION PLANS                
Maximum number of awards that may be granted to an individual per calendar year (in shares)         250,000      
2007 Plan | Restricted Shares                
SHARE-BASED COMPENSATION PLANS                
Maximum number of shares reserved for issuance         465,045      
2004 Plan                
SHARE-BASED COMPENSATION PLANS                
Maximum number of shares reserved for issuance           3,000,000    
Number of Shares Under Option                
Balance at the end of the period (in shares)         5,000