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Debt (Details Textual) - USD ($) $ in Millions | 6 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Jun. 30, 2016 | Dec. 31, 2017 | Dec. 31, 2016
Debt Instrument [Line Items] |  |  |
Letters of Credit Outstanding, Amount |  | $ 20.9 | $ 23.7
Long-term Line of Credit |  | 79.0 | 59.1
Debt Issuance Costs, Line of Credit Arrangements, Net |  | $ 0.8 |
Debt Instrument Covenant Leveraged Debt Ratio Restriction |  | 2.25 |
Insurance Programe Obligations [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Letters of Credit Outstanding, Amount |  | $ 17.6 | 17.6
Contract Performance Obligations [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Letters of Credit Outstanding, Amount |  | $ 3.3 | $ 6.1
Maximum [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Leveraged debt ratio | 3.0 |  |
Leverage Coverage Ratio Expansion | 3.5 |  |
Maximum [Member] | Revolving Credit Facility [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage |  | 0.375% |
Maximum [Member] | Performance letters of credit [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Letter of credit fee (as a percent) |  | 1.125% |
Maximum [Member] | Non-performance Letters Of Credit [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate margin (as a percent) |  | 2.125% |
Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate margin (as a percent) |  | 2.00% |
Maximum [Member] | Base Rate [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate margin (as a percent) |  | 1.00% |
Minimum [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Interest coverage ratio | 3.0 |  |
Minimum [Member] | Revolving Credit Facility [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage |  | 0.20% |
Minimum [Member] | Performance letters of credit [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Letter of credit fee (as a percent) |  | 0.625% |
Minimum [Member] | Non-performance Letters Of Credit [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate margin (as a percent) |  | 1.125% |
Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate margin (as a percent) |  | 1.00% |
Minimum [Member] | Base Rate [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Interest rate margin (as a percent) |  | 0.00% |
Swing line Loans [Member] | Facility [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Maximum borrowing capacity |  | $ 25.0 |
Syndicated Credit Agreement [Member] | Facility [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Option to increase borrowing capacity | $ 100.0 |  |
Maximum borrowing capacity | $ 250.0 |  |
Syndicated Credit Agreement [Member] | Facility [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Maximum borrowing capacity |  | $ 175.0 |
Credit Agreement [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt, Weighted Average Interest Rate |  | 2.07% |
Credit Agreement [Member] | Facility [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Percentage of Capital Stock From Direct Foreign Subsidiaries | 65.00% |  |
Maximum Acquisition Consideration Under Credit Agreement |  | $ 50.0 |
Credit Agreement [Member] | Foreign Revolving Loans and Letters of Credit [Member] | Facility [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Maximum borrowing capacity | $ 50.0 |  |

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- Definition The Company has the option to expand the debt coverage ratio to 3.5 in the event of an acquisition in excess of $30 million. The expansion occurs in the quarter the acquisition is consummated and shall continue in effect for the next four consecutive quarters. + References No definition available. + Details
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- Definition Amount, after accumulated amortization, of debt issuance costs related to line of credit arrangements. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section S45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=68176171&loc=SL68176184-208336 + Details
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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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