Pensions and Other Post-Employment Benefits (Details 5) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Summary of fair values of the Company's defined benefit pension plan assets
DefinedBenefitPlanFairValueofPlanAssetsExcludingNetAssetValueInvestments	$ 178,803	$ 175,112
Fair Value of Plan Assets	234,976	199,992
Cash
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	10,604	10,124
U.S. Equities
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	54,376	53,983
International Equities
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	39,010	30,732
Emerging Markets Equities
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	15,843	11,792
Intermediate-term bonds
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	34,187	48,138
Short-term bonds
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	612	3,150
Global bonds
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	7,492	2,121
Real estate fund
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	6,617	5,929
Alternative Strategies
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	9,948	9,036
Accrued Interest and Dividends
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	114	107
Pooled Investment Fund
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	21,378	20,418
Multi-strategy hedge funds
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	3,970	4,320
Common/Collective trusts
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	8,942
Intermediate-term bonds at NAV
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	21,771
Private equity funds
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	112	142
Level 1
Summary of fair values of the Company's defined benefit pension plan assets
DefinedBenefitPlanFairValueofPlanAssetsExcludingNetAssetValueInvestments	161,795	146,504
Level 1 | Cash
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	10,604	10,124
Level 1 | U.S. Equities
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	53,659	53,358
Level 1 | International Equities
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	35,016	27,304
Level 1 | Emerging Markets Equities
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	15,586	11,562
Level 1 | Intermediate-term bonds
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	25,653	29,429
Level 1 | Short-term bonds
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	0	0
Level 1 | Global bonds
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	4,986	0
Level 1 | Real estate fund
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	6,284	5,639
Level 1 | Alternative Strategies
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	9,893	8,981
Level 1 | Accrued Interest and Dividends
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	114	107
Level 2
Summary of fair values of the Company's defined benefit pension plan assets
DefinedBenefitPlanFairValueofPlanAssetsExcludingNetAssetValueInvestments	17,008	28,608
Level 2 | Cash
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	0	0
Level 2 | U.S. Equities
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	717	625
Level 2 | International Equities
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	3,994	3,428
Level 2 | Emerging Markets Equities
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	257	230
Level 2 | Intermediate-term bonds
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	8,534	18,709
Level 2 | Short-term bonds
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	612	3,150
Level 2 | Global bonds
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	2,506	2,121
Level 2 | Real estate fund
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	333	290
Level 2 | Alternative Strategies
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	55	55
Level 2 | Accrued Interest and Dividends
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	0	0
Level 3
Summary of fair values of the Company's defined benefit pension plan assets
DefinedBenefitPlanFairValueofPlanAssetsExcludingNetAssetValueInvestments	0	0
Level 3 | Cash
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	0	0
Level 3 | U.S. Equities
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	0	0
Level 3 | International Equities
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	0	0
Level 3 | Emerging Markets Equities
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	0	0
Level 3 | Intermediate-term bonds
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	0	0
Level 3 | Short-term bonds
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	0	0
Level 3 | Global bonds
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	0	0
Level 3 | Real estate fund
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	0	0
Level 3 | Alternative Strategies
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	0	0
Level 3 | Accrued Interest and Dividends
Summary of fair values of the Company's defined benefit pension plan assets
Fair Value of Plan Assets	$ 0	$ 0