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The following table summarizes information regarding Restricted Shares: 

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Unvested Restricted Shares outstanding as of December 31, 2019, includes approximately 647,000 units with performance-based vesting provisions. Performance-based units are issuable in common stock and vest upon the achievement of pre-defined performance targets. Performance-based units have performance targets based on our average return on invested capital and our total shareholder return ("TSR") over a three-year period. Most unvested units were granted in three annual grants since January 1, 2017 and have a vesting percentage between 0% and 200% depending on the achievement of the specific performance targets. Except for shares granted under the 55/10 Provision, compensation expense is recognized ratably over a cliff-vesting period of 36 months, based on the fair value of our common stock on the date of grant, as adjusted for actual forfeitures. During the performance period, earned and unearned compensation expense is adjusted based on changes in the expected achievement of the performance targets for all performance-based units granted except for the TSR-based units. Vesting provisions range from 0 to approximately 1,294,000 shares based on performance targets. As of December 31, 2019, we estimate vesting of approximately 466,000 shares based on expected achievement of performance targets. 

## 8. DERIVATIVES AND HEDGING ACTIVITIES 

Our risk management and foreign currency derivatives and hedging policy specifies the conditions under which we may enter into derivative contracts. See Note 1 for additional information on our purpose for entering into derivatives and our overall risk management strategies. We enter into foreign exchange forward contracts to hedge our cash flow risks associated with transactions denominated in currencies other than the local currency of the operation engaging in the transaction. 

Foreign exchange contracts had notional values of $398.5 million and $280.9 million at December 31, 2019 and 2018, respectively. At December 31, 2019, the length of foreign exchange contracts currently in place ranged from 17 days to 32 months. 

We are exposed to risk from credit-related losses resulting from nonperformance by counterparties to our financial instruments. We perform credit evaluations of our counterparties under forward exchange contracts and expect all counterparties to meet their obligations. We have not experienced credit losses from our counterparties. 

The fair values of foreign exchange contracts are summarized below: 

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Current and noncurrent derivative assets are reported in our consolidated balance sheets in prepaid expenses and other and other assets, net, respectively. Current and noncurrent derivative liabilities are reported in our consolidated balance sheets in accrued liabilities and retirement obligations and other liabilities, respectively. 

