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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 |  |  |

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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iv)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The risk-free interest rate assumption that is used in valuing an option on its own shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iv) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iv)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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