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Commitments and Contingencies - Rental Expense and Letters of Credit (Details) | 12 Months Ended
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Dec. 31, 2017 USD ($) item | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Operating Lease Obligations |  |  |
Rental expense under operating leases | $ 1,785,000 | $ 1,907,000 | $ 1,691,000
Obligations related to health insurance and self-insured workers' compensation |  |  |
Number of letters of credit issued | item | 3 |  |
Insurance Obligations |  |  |
Obligations related to health insurance and self-insured workers' compensation |  |  |
Letters of credit issued | $ 1,767,000 |  |
Workers' Compensation Insurance |  |  |
Obligations related to health insurance and self-insured workers' compensation |  |  |
Letters of credit issued | 583,000 |  |
Performance Obligations |  |  |
Obligations related to health insurance and self-insured workers' compensation |  |  |
Letters of credit issued | 75,000 |  |
Letter Of Credit |  |  |
Obligations related to health insurance and self-insured workers' compensation |  |  |
Funds borrowed under Line of Credit | $ 0 |  |

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- Definition Represents the number of letters of credit issued and outstanding. + References No definition available. + Details
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Balance Type: | na
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- Definition Operating Lease Obligations [Line Items] + References No definition available. + Details
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- Definition Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line. + References No definition available. + Details
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Balance Type: | debit
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- Definition The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. + References No definition available. + Details
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Balance Type: | credit
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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
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- Details
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- Details
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