Debt (Schedule of Debt) (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Revolving credit facility	$ 110,000	$ 121,000
Debt:
Total debt	4,974	8,044
Less: current portion	(3,184)	(4,192)
Total long-term debt, net	1,790	3,852
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Revolving credit facility	$ 110,000	121,000
Debt:
Debt, maturity	September 2021
Maximum [Member] \| Revolving Credit Facility [Member]
Debt:
Interest rate	3.15%
Minimum [Member] \| Revolving Credit Facility [Member]
Debt:
Interest rate	3.04%
PST Short-Term Notes [Member]
Debt Instrument [Line Items]
Short-term debt	$ 1,056
Debt:
Debt, maturity	March 2019
Interest rate	11.26%
PST Short-Term Notes [Member] \| Maximum [Member]
Debt:
Interest rate	11.64%
PST Short-Term Notes [Member] \| Minimum [Member]
Debt:
Interest rate	9.00%
PST Long-Term Notes [Member]
Debt:
Total long-term debt, net	$ 3,915	8,016
Debt maturity period range start	2019
Debt maturity period range end	2021
Other [Member]
Debt:
Total debt	$ 3	$ 28

Latest period the outstanding debt instruments are required to be repaid.

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Earliest period the outstanding debt instruments are required to be repaid.

+ References

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- Definition

Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13,16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

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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.

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Description of the maturity date of the debt instrument including whether the debt matures serially and, if so, a brief description of the serial maturities.

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- Definition

Fair value of the amount outstanding under the credit facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13476-108611

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- References

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ 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(19)(a))
-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 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: 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(a)(16)(a)(1))
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