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STOCK-BASED COMPENSATION (Tables) | 12 Months Ended
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Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract] |
Schedule of Share-based Compensation, Stock Options and Stock Appreciation Rights Award Activity | The following table sets forth a summary of stock-settled stock appreciation rights and related information for the years indicated:
| 2016 |  | 2015 |  | 2014
| Awards |  | Weighted-Average Exercise Price |  | Weighted-Average Remaining Contractual Life |  | Aggregate Intrinsic Value (In thousands) |  | Awards |  | Weighted-Average Exercise Price |  | Awards |  | Weighted-Average Exercise Price
Beginning of year | 2,567,021 |  |  | $ | 54.47 |  |  |  |  |  |  | 2,480,745 |  |  | $ | 50.91 |  |  | 2,715,651 |  |  | $ | 45.93 |
Granted | 709,999 |  |  | 42.63 |  |  |  |  |  |  | 394,182 |  |  | 69.54 |  |  | 274,508 |  |  | 85.35 |
Exercised | (526,818 | ) |  | 41.54 |  |  |  |  |  |  | (232,542 | ) |  | 35.80 |  |  | (485,469 | ) |  | 41.58 |
Canceled | (310,715 | ) |  | 63.71 |  |  |  |  |  |  | (75,364 | ) |  | 73.59 |  |  | (23,945 | ) |  | 70.30 |
End of year | 2,439,487 |  |  | 52.62 |  |  | 5.6 |  | $ | 40,135 |  |  | 2,567,021 |  |  | 54.47 |  |  | 2,480,745 |  |  | 50.91 |
Exercisable at end of year | 1,549,350 |  |  | $ | 53.35 |  |  | 3.8 |  | $ | 24,903 |  |  | 2,034,263 |  |  | $ | 49.36 |  |  | 1,980,767 |  |  | $ | 44.06 |
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] | WESCO granted the following stock-settled stock appreciation rights at the following weighted-average assumptions:
| 2016 |  | 2015 |  | 2014
Stock-settled stock appreciation rights granted | 709,999 |  | 394,182 |  | 274,508
Risk free interest rate | 1.2% |  | 1.6% |  | 1.5%
Expected life (in years) | 5 |  | 5 |  | 5
Expected volatility | 32% |  | 32% |  | 39%
Schedule of Share-based Compensation, Restricted Stock Units Award Activity | The following table sets forth a summary of time-based restricted stock units and related information for the year ended December 31, 2016:
| Awards |  | Weighted-Average Fair Value
Unvested at December 31, 2015 | 175,411 |  |  | $ | 74.52 |
Granted | 162,256 |  |  | 44.45 |
Vested | (60,015 | ) |  | 72.41 |
Forfeited | (20,556 | ) |  | 59.15 |
Unvested at December 31, 2016 | 257,096 |  |  | $ | 57.47 |
The following table sets forth a summary of performance-based awards for the year ended December 31, 2016:
| Awards |  | Weighted-Average Fair Value
Unvested at December 31, 2015 | 114,520 |  |  | $ | 76.48 |
Granted | 91,768 |  |  | 47.00 |
Vested | — |  |  | — |
Forfeited | (56,968 | ) |  | 71.25 |
Unvested at December 31, 2016 | 149,320 |  |  | $ | 60.36 |
Schedule of Share-based Payment Award, Performance-based Awards, Valuation Assumptions [Table Text Block] | The fair value of the performance shares based on total stockholder return granted during the year ended December 31, 2016 were estimated using the following weighted-average assumptions:
Weighted-Average Assumptions
Grant date share price | $ | 42.44 |
WESCO expected volatility | 26.3 | %
Peer group median volatility | 24.2 | %
Risk-free interest rate | 0.89 | %
Correlation | 121.5 | %

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- Definition Tabular disclosure of the number and weighted-average exercise prices (or conversion ratios) for stock options and stock appreciation rights that were outstanding at the beginning and end of the year, exercisable at the end of the year, and the number of stock options and stock appreciation rights that were granted, exercised or converted, forfeited, and expired during the year. + 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) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + 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) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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