Debt (Details Textual) - USD ($) $ in Thousands	1 Months Ended	6 Months Ended	12 Months Ended
Jun. 15, 2015	Jun. 30, 2015	Dec. 31, 2014
Current Unsecured Bank Credit Facility [Member]
Debt
Line of Credit Facility, Expiration Date		Jul. 30, 2019
Debt Instrument, Increase (Decrease), Other, Net	$ 75,000
Senior Notes 2015 [Member]
Debt
Debt Instrument, Increase (Decrease), Other, Net	$ (75,000)
Senior Notes 2015 [Member] \| Senior Note 6.05 % [Member]
Debt
Unaccrued discount		$ 0	$ 11
Senior Notes		6.05%
Aggregate principal amount		$ 75,000	$ 75,000
Maturity date of Senior note		Jun. 15, 2015	Jun. 15, 2015
Imputed rate		6.10%	6.10%
Senior Notes 2016 [Member] \| Senior Note 6.85 % [Member]
Debt
Unaccrued discount		$ 31	$ 50
Senior Notes		6.85%
Aggregate principal amount		$ 125,000	$ 125,000
Maturity date of Senior note		Apr. 15, 2016	Apr. 15, 2016
Imputed rate		6.90%	6.90%

No definition available.

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

+ Details

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- Definition

Net increase or decrease in the carrying amount of the debt instrument for the period for reasons other than accrued but unpaid interest, additional borrowings, forgiveness and repayments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(f))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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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

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(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

+ Details

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- Definition

The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 1A

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28541-108399

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-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

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Balance Type:	debit
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- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ References

+ Details

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