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Stock-Based Compensation - Compensation Expense for Periods Included in Continuing Operations (Detail) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
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Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Restricted Stock Units (RSU) and Performance Share Awards (PSAs) [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Compensation expense | $ 1,146 | $ 1,494 | $ 4,283 | $ 3,293
Stock Only Stock Appreciation Rights (SOSARs) [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Compensation expense | $ 67 | $ 233 | $ 311 | $ 1,038

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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