| Income Taxes - Significant Components of Company's Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017 | 
|---|---|---|
| Deferred Tax Assets: | ||
| Asset Reserves | $ 8,808 | $ 7,596 | 
| Deferred Compensation | 5,628 | 6,091 | 
| Capital Lease Basis Difference | 1,743 | 1,002 | 
| State Investment and Research and Development Tax Credit Carryforwards, Net of Federal Tax | 1,066 | 1,379 | 
| Customer Advanced Payments and Deferred Revenue | 875 | 1,007 | 
| State Net Operating Loss Carryforwards and Other | 8,281 | 8,115 | 
| Total Gross Deferred Tax Assets | 26,401 | 25,190 | 
| Valuation Allowance for Foreign Tax Credit, State Deferred Tax Assets and Tax Credit Carryforwards, Net of Federal Tax | (8,098) | (7,823) | 
| Deferred Tax Assets | 18,303 | 17,367 | 
| Deferred Tax Liabilities: | ||
| Depreciation | 11,687 | 9,267 | 
| Goodwill and Intangible Assets | 4,438 | 7,275 | 
| Other | 3,812 | 3,130 | 
| Deferred Tax Liabilities | 19,937 | 19,672 | 
| Net Deferred Tax Liabilities | $ (1,634) | $ (2,305) | 
| X | ||||||||||
| 
- Definition Capital Lease Assets Basis Difference No definition available. 
 | 
| X | ||||||||||
| 
- Definition Deferred tax assets customer advanced payments and deferred revenue. No definition available. 
 | 
| X | ||||||||||
| 
- References No definition available. 
 | 
| X | ||||||||||
| 
- Definition Amount of deferred tax liability attributable to taxable temporary differences. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 | 
| X | ||||||||||
| 
- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 | 
| X | ||||||||||
| 
- Definition Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 | 
| X | ||||||||||
| 
- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible state and local operating loss carryforwards. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 | 
| X | ||||||||||
| 
- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible general business tax credit carryforwards. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 | 
| X | ||||||||||
| 
- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from compensation and benefits costs. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 | 
| X | ||||||||||
| 
- Definition Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary differences from reserves, classified as other. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 | 
| X | ||||||||||
| 
- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 | 
| X | ||||||||||
| 
- Definition Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences without jurisdictional netting. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 | 
| X | ||||||||||
| 
- References No definition available. 
 | 
| X | ||||||||||
| 
- Definition Amount of deferred tax liability attributable to taxable temporary differences from intangible assets including goodwill. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 | 
| X | ||||||||||
| 
- Definition Amount of deferred tax liability attributable to taxable temporary differences classified as other. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 | 
| X | ||||||||||
| 
- Definition Amount of deferred tax liability attributable to taxable temporary differences from property, plant, and equipment. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
 |