Retirement Plans - Reconciliation of Level 3 Hedge Fund Asset Within Fair Value Hierarchy (Details 11) $ in Thousands	12 Months Ended
Dec. 31, 2016 USD ($)
Reconciliation of Level 3 fund assets
Beginning Balance	$ 290,795
Ending Balance	293,567
International hedge funds
Reconciliation of Level 3 fund assets
Beginning Balance	25,191
Ending Balance	23,542
Significant Unobservable Inputs (Level 3)
Reconciliation of Level 3 fund assets
Beginning Balance	13,360
Ending Balance	12,862
Significant Unobservable Inputs (Level 3) \| International hedge funds
Reconciliation of Level 3 fund assets
Beginning Balance	0
Ending Balance	$ 0

Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

Reference 1: 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=64937038&loc=d3e12355-114930

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)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Plan Assets
-URI http://asc.fasb.org/extlink&oid=6749337

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Plan Assets
-URI http://asc.fasb.org/extlink&oid=6520858

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Balance Type:	debit
Period Type:	instant