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STOCKHOLDERS' EQUITY - Stock Based Compensation (Details) - USD ($) |  | 12 Months Ended
--- | --- | ---
Jan. 18, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Total charge to operations: |  |  |  |
Share based compensation charged to operations |  | $ 3,133,000 | $ 2,983,000 | $ 2,334,000
Compensation costs related to non-vested awards that have not yet been recognized |  | $ 7,098,000 |  |
Restricted stock |  |  |  |
Stock Based Compensation |  |  |  |
Vesting period |  | 5 years |  |
Summary of the activity of the incentive plans |  |  |  |
Number of shares |  | 140,100 | 139,225 | 129,975
Average per share grant price (in dollars per share) |  | $ 24.75 | $ 21.74 | $ 24.60
Deferred compensation to be recognized over vesting period |  | $ 3,467,000 | $ 3,027,000 | $ 3,197,000
Number of non-vested shares: |  |  |  |
Non-vested beginning of year (in shares) |  | 591,750 | 538,755 | 480,995
Grants (in shares) |  | 140,100 | 139,225 | 129,975
Vested during year (in shares) |  | (118,450) | (85,730) | (72,215)
Forfeitures (in shares) |  | (500) | (500) |
Non-vested end of year (in shares) |  | 612,900 | 591,750 | 538,755
Restricted stock and RSU grants: |  |  |  |
Weighted average per share value of non-vested shares (based on grant price) (in dollars per share) |  | $ 22.89 | $ 17.95 | $ 17.12
Value of stock vested during the year (based on grant price) |  | $ 3,008,000 | $ 1,451,500 | $ 612,000
Weighted average per share value of shares forfeited during the year (based on grant price) (in dollars per share) |  | $ 8.37 | $ 21.05 |
Total charge to operations: |  |  |  |
Share based compensation charged to operations |  | $ 2,966,000 | $ 2,692,000 | $ 2,204,000
Approximate weighted average vesting period |  | 2 years 2 months 12 days |  |
RSUs |  |  |  |
Stock Based Compensation |  |  |  |
Percentage of units to be vested on satisfaction of performance criteria of average total stockholder return |  | 50.00% |  |
Percent of number of units to be vested on satisfaction of performance criteria related to average annual return on capital |  | 50.00% |  |
Summary of the activity of the incentive plans |  |  |  |
Number of shares |  | 76,250 |  |
Average per share grant price (in dollars per share) |  | $ 24.03 |  |
Deferred compensation to be recognized over vesting period |  | $ 1,004,000 |  |
Number of non-vested shares: |  |  |  |
Non-vested beginning of year (in shares) |  | 200,000 | 200,000 | 200,000
Grants (in shares) |  | 76,250 |  |
Vested during year (in shares) |  | (113,584) |  |
Forfeitures (in shares) |  | (86,416) |  |
Non-vested end of year (in shares) |  | 76,250 | 200,000 | 200,000
Total charge to operations: |  |  |  |
Share based compensation charged to operations |  | $ 167,000 | $ 291,000 | $ 130,000
Approximate weighted average vesting period |  | 2 years 6 months |  |
TSR awards |  |  |  |
Stock Based Compensation |  |  |  |
Expected life |  | 3 years |  |
Dividend rate |  | 7.16% |  |
Risk-free interest rate minimum |  | 1.14% |  |
Risk-free interest rate maximum |  | 1.64% |  |
Expected price volatility minimum |  | 16.57% |  |
Expected price volatility maximum |  | 19.16% |  |
2016 Incentive Plan |  |  |  |
Stock Based Compensation |  |  |  |
Number of shares authorized for issuance |  | 750,000 |  |
Aggregate value of restricted shares granted | $ 3,664,000 |  |  |
Summary of the activity of the incentive plans |  |  |  |
Number of shares | 144,750 |  |  |
Number of non-vested shares: |  |  |  |
Grants (in shares) | 144,750 |  |  |
2016 Incentive Plan | Restricted stock |  |  |  |
Summary of the activity of the incentive plans |  |  |  |
Number of shares |  | 140,100 |  |
Number of non-vested shares: |  |  |  |
Grants (in shares) |  | 140,100 |  |
Vested during year (in shares) |  | (3,000) |  |
Forfeitures (in shares) |  | (100) |  |
2016 Incentive Plan | RSUs |  |  |  |
Summary of the activity of the incentive plans |  |  |  |
Number of shares |  | 76,250 |  |
Number of non-vested shares: |  |  |  |
Grants (in shares) |  | 76,250 |  |
Non-vested end of year (in shares) |  | 76,250 |  |
2012 Incentive Plan |  |  |  |
Stock Based Compensation |  |  |  |
Shares issued pursuant to plan |  | 500,700 |  |
Shares forfeited pursuant to Plan |  | 3,350 |  |
Shares vested pursuant to plan |  | 21,450 |  |
Pay-for-performance program | RSUs | General and administrative expense |  |  |  |
Summary of the activity of the incentive plans |  |  |  |
Deferred compensation to be recognized over vesting period |  | $ 1,004,000 |  |

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