| Share-Based Compensation and Cash-Based Incentive Compensation - Summary of Incentive Compensation Expense under Share-Based Payment Arrangements and Related Tax Benefit (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
| Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017 | |
| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] | ||||
| Share-based compensation | $ 1,374 | $ 1,984 | $ 3,808 | $ 6,324 | 
| Tax benefit computed at the statutory rate | 289 | 694 | 800 | 2,213 | 
| Restricted Stock Units (RSUs) | ||||
| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] | ||||
| Share-based compensation | 1,304 | 1,914 | 3,598 | 6,114 | 
| Restricted Shares | ||||
| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] | ||||
| Share-based compensation | $ 70 | $ 70 | $ 210 | $ 210 | 
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- Definition The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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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. No definition available. 
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- Definition Share-based compensation paid in shares and cash. No definition available. 
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- Details 
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- Details 
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