Benefit Plans - Components of Net Periodic Benefit Cost and Other Amounts Recognized in Other Comprehensive Income (Loss) (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Components of net periodic benefit cost
Service cost	$ (4,331,000)us-gaap_DefinedBenefitPlanServiceCost	$ (4,817,000)us-gaap_DefinedBenefitPlanServiceCost	$ (4,271,000)us-gaap_DefinedBenefitPlanServiceCost
Interest cost	(4,577,000)us-gaap_DefinedBenefitPlanInterestCost	(4,223,000)us-gaap_DefinedBenefitPlanInterestCost	(4,048,000)us-gaap_DefinedBenefitPlanInterestCost
Expected return on plan assets	10,869,000	9,536,000	8,742,000
Net periodic benefit income (cost)	(1,942,000)	2,227,000	1,305,000
Other amounts recognized in other comprehensive (Loss)
Change to net actuarial (loss) gain for the period	(14,276,000)	30,409,000	(11,236,000)
Amortization of prior service cost	(19,000)	(20,000)	(20,000)
Defined Benefit Plan, Future Amortization of Gain (Loss)	0	(2,703,000)	(1,708,000)
Amortization of net loss	0	2,703,000	1,708,000
Total recognized in other comprehensive (loss) income	(14,257,000)	33,132,000	(9,508,000)
Total recognized in net benefit cost and other comprehensive (loss) income	$ (12,315,000)	$ 30,905,000	$ (10,813,000)

Total recognized in net benefit cost and other comprehensive (loss)/income.

No definition available.

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- Definition

The amount of gains or losses recognized in net periodic benefit cost.

+ References

+ Details

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- Definition

The amount of the prior service cost or credit recognized in net periodic benefit cost relating to benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation.

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- Definition

Amount before tax, after reclassification adjustments, of actuarial gain (loss) that has not been recognized in the income statement.

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- Definition

An amount calculated as a basis for determining the extent of delayed recognition of the effects of changes in the fair value of assets. The expected return on plan assets is determined based on the expected long-term rate of return on plan assets and the market-related value of plan assets.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Glossary Expected Return on Plan Assets

-URI http://asc.fasb.org/extlink&oid=6512136

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 60

-Glossary Expected Return on Plan Assets

-URI http://asc.fasb.org/extlink&oid=6512171

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (h)(3)

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

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- Definition

Amount included in accumulated other comprehensive income (AOCI) related to gain (loss) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position.

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No definition available.

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- Definition

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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- Definition

The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments.

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- Definition

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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (h)(1)

-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

-Glossary Service Cost (Component of Net Periodic Pension Cost)

-URI http://asc.fasb.org/extlink&oid=6525008

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-Publisher FASB

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- Definition

Amount before tax of cost (credit) of benefit changes attributable to plan participants' prior service resulting from a plan amendment or plan initiation that has not been recognized in net periodic benefit cost (credit).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 11

-URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e637-108580

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