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Stock-Based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2017
Restricted Stock Units (RSU) and Performance Share Awards (PSAs) [Member] |
Summary of Share Based Compensation Activity | The following table summarizes RSU and PSA activity during the past three years:
Units | 2017 |  |  |  | 2016 |  |  |  | 2015 |
Balance at January 1, |  | 679,038 |  |  |  |  | 674,523 |  |  |  |  | 888,942 |
Granted |  | 375,435 |  |  |  |  | 302,722 |  |  |  |  | 164,666 |
Forfeited |  | (96,306 | ) |  |  |  | (148,232 | ) |  |  |  | (92,183 | )
Shares delivered |  | (28,781 | ) |  |  |  | (149,975 | ) |  |  |  | (286,902 | )
Balance at December 31, |  | 929,386 |  |  |  |  | 679,038 |  |  |  |  | 674,523 |
Compensation Expense for Stock Option Activity |
| 2017 |  |  |  | 2016 |  |  |  | 2015 |
Compensation expense | $ | 4,843 |  |  |  | $ | 3,154 |  |  |  | $ | 1,758 |
Stock Only Stock Appreciation Rights (SOSARs) [Member] |
Summary of Share Based Compensation Activity | The following table sets forth information related to outstanding SOSARS:
| 2017 |  |  |  | 2016 |  |  | 2015 |  |
SOSARS | Shares |  |  |  | Wtd Avg Exercise Price |  |  |  | Shares |  |  | Wtd Avg Exercise Price |  |  | Shares |  |  | Wtd Avg Exercise Price |  |
Outstanding at January 1, |  | 2,736,616 |  |  |  | $ | 17.64 |  |  |  |  | 2,199,742 |  |  | $ | 17.82 |  |  |  | 1,864,707 |  |  | $ | 16.20 |  |
Granted |  | — |  |  |  |  | — |  |  |  |  | 743,925 |  |  |  | 17.54 |  |  |  | 423,590 |  |  | 24.62 |  |
Exercised |  | (157,140 | ) |  |  |  | 13.76 |  |  |  |  | (61,190 | ) |  |  | 10.70 |  |  |  | (70,347 | ) |  |  | 14.12 |  |
Canceled / forfeited |  | (17,630 | ) |  |  |  | 18.46 |  |  |  |  | (145,861 | ) |  |  | 22.80 |  |  |  | (18,208 | ) |  |  | 25.41 |  |
Outstanding at December 31, |  | 2,561,846 |  |  |  | $ | 17.87 |  |  |  |  | 2,736,616 |  |  | $ | 17.64 |  |  |  | 2,199,742 |  |  | $ | 17.82 |  |
Exercisable at December 31, |  | 2,011,075 |  |  |  |  | 17.56 |  |  |  |  | 1,740,591 |  |  | 16.19 |  |  |  | 1,504,599 |  |  |  | 14.48 |  |
Vested and expected to vest |  | 2,561,846 |  |  |  |  |  |  |  |  |  | 2,725,611 |  |  |  |  |  |  |  | 2,178,708 |  |  |  |  |  |
SOSAR Grants |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted average grant date fair value per share |  | — |  |  |  |  |  |  |  |  | $ | 4.07 |  |  |  |  |  |  | $ | 7.46 |  |  |  |  |  |
Aggregate grant date fair value (in thousands) |  | — |  |  |  |  |  |  |  |  | $ | 3,013 |  |  |  |  |  |  | $ | 3,134 |  |  |  |  |  |
Black-Scholes assumptions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Dividend yield |  | — |  |  |  |  |  |  |  |  |  | 2.85 | % |  |  |  |  |  |  | 1.94 | % |  |  |  |  |
Risk free rate of return |  | — |  |  |  |  |  |  |  |  |  | 1.34 | % |  |  |  |  |  |  | 1.64 | % |  |  |  |  |
Volatility |  | — |  |  |  |  |  |  |  |  |  | 31.97 | % |  |  |  |  |  |  | 36.38 | % |  |  |  |  |
Expected life |  | — |  |  |  |  |  |  |  |  | 6 |  |  |  |  |  |  | 6 |  |  |  |  |  |
Compensation expense (in thousands) | $ | 1,371 |  |  |  |  |  |  |  |  | $ | 2,735 |  |  |  |  |  |  | $ | 2,645 |  |  |  |  |  |

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- Definition Tabular disclosure of components of a stock option or other award plan under which equity-based compensation is awarded to employees, typically comprised of the amount of unearned compensation (deferred compensation cost), compensation expense, and changes in the quantity and fair value of the shares (or other type of equity) granted, exercised, forfeited, and issued and outstanding pertaining to that plan. Disclosure may also include nature and general terms of such arrangements that existed during the period and potential effects of those arrangements on shareholders, effect of compensation cost arising from equity-based payment arrangements on the income statement, method of estimating the fair value of the goods or services received, or the fair value of the equity instruments granted, during the period, cash flow effects resulting from equity-based payment arrangements and, for registrants that accelerate vesting of out of the money share options, reasons for the decision to accelerate. + 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=96867065&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901 + Details
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