Employee Retirement Plans - Asset Allocation (Details) (Pension plan, USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee retirement plans
Target (as a percent)	100.00%
Actual allocation of pension plan assets	$ 26,046	$ 24,638	$ 21,808
Weighted-average asset allocation (as a percent)	100.00%	100.00%
Large Cap Equity
Employee retirement plans
Target (as a percent)	37.00%
Actual allocation of pension plan assets	9,417	7,373
Weighted-average asset allocation (as a percent)	36.00%	30.00%
Mid Cap Equity
Employee retirement plans
Target (as a percent)	4.00%
Actual allocation of pension plan assets	1,005	938
Weighted-average asset allocation (as a percent)	4.00%	4.00%
Small Cap Equity
Employee retirement plans
Target (as a percent)	3.00%
Actual allocation of pension plan assets	1,019	935
Weighted-average asset allocation (as a percent)	4.00%	4.00%
International Equity
Employee retirement plans
Target (as a percent)	12.00%
Actual allocation of pension plan assets	2,546	2,485
Weighted-average asset allocation (as a percent)	10.00%	10.00%
Emerging markets Equity
Employee retirement plans
Target (as a percent)	2.00%
Actual allocation of pension plan assets	645	617
Weighted-average asset allocation (as a percent)	2.00%	2.00%
Fixed Income and Cash Equivalents
Employee retirement plans
Target (as a percent)	34.00%
Actual allocation of pension plan assets	8,794	9,830
Weighted-average asset allocation (as a percent)	34.00%	40.00%
Real Estate
Employee retirement plans
Target (as a percent)	8.00%
Actual allocation of pension plan assets	$ 2,620	$ 2,460
Weighted-average asset allocation (as a percent)	10.00%	10.00%

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Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Section 35

-Paragraph 50

-URI http://asc.fasb.org/extlink&oid=29635418&loc=d3e12355-114930

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- Definition

Target allocation of investments of this type to total plan assets presented on a weighted average basis.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (d)(i)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 5

-Subparagraph (c)(i)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2446-114920

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- Definition

Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 5

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2446-114920

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (d)(1)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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