Benefit Plans - Plan Assets and Benefit Obligation Activity (Details) (USD $) In Thousands, unless otherwise specified	1 Months Ended	12 Months Ended
Jan. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Change in fair value of plan assets
Fair value at beginning of measurement period	$ 117,768	$ 152,739	$ 117,768
Actual return on plan assets		15,511	31,518
Company contributions	12,638	0	12,638
Benefits paid		(7,652)us-gaap_DefinedBenefitPlanBenefitsPaid	(9,185)us-gaap_DefinedBenefitPlanBenefitsPaid
Fair value at end of measurement period		160,598	152,739	117,768
Change in benefit obligation
Projected benefit obligation at beginning of measurement period	97,653	89,179	97,653
Service cost		4,331us-gaap_DefinedBenefitPlanServiceCost	4,817us-gaap_DefinedBenefitPlanServiceCost	4,271us-gaap_DefinedBenefitPlanServiceCost
Interest cost		4,577us-gaap_DefinedBenefitPlanInterestCost	4,223us-gaap_DefinedBenefitPlanInterestCost	4,048us-gaap_DefinedBenefitPlanInterestCost
Actuarial (gains) loss		18,893	(8,329)
Benefits paid		(7,652)us-gaap_DefinedBenefitPlanBenefitsPaid	(9,185)us-gaap_DefinedBenefitPlanBenefitsPaid
Projected benefit obligation at the end of measurement period		109,328	89,179	97,653
Funded status at end of year (fair value of plan assets less benefit obligation)		$ 51,270	$ 63,560

The difference between fair value of plan assets at the end of the period and the fair value at the beginning of the period, adjusted for contributions and payments of benefits during the period, and after adjusting for taxes and other expenses, as applicable.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Actual Return on Plan Assets (Component of Net Periodic Postretirement Benefit Cost)

-URI http://asc.fasb.org/extlink&oid=6504192

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)(1)

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

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Actual Return on Plan Assets (Component of Net Periodic Pension Cost)

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- Definition

Amount of gain (loss) related to change in benefit obligation resulting from changes in actuarial assumptions, for example, but not limited to, interest, mortality, employee turnover, salary, and temporary deviation from the substantive plan.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

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-URI http://asc.fasb.org/extlink&oid=6514294

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1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date.

+ References

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

-Publisher FASB

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-Publisher FASB

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-URI http://asc.fasb.org/extlink&oid=6522206

Reference 3: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

-Glossary Accumulated Postretirement Benefit Obligation

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The amount of payments made for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment. Also includes payments made under a postretirement benefit plan, including prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. This item represents a periodic decrease to the plan obligations and a decrease to plan assets.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Postretirement Benefits

-URI http://asc.fasb.org/extlink&oid=6521376

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- Definition

The increase in the fair value of plan assets from contributions made by the employer.

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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.

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The funded status is measured as the difference between the fair value of plan assets and the benefit obligation. Will normally be the same as the net Defined Benefit Plan, Amounts Recognized in Balance Sheet, Total.

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The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

+ References

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