Pensions and Other Postemployment Benefits - Components of Net Periodic Benefit Cost (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 6 Months Ended
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
Jun. 30, 2013
Pension Benefits
        
Defined Benefit Plan Disclosure [Line Items]        
Service cost $ 0 $ 0 $ 0 $ 0
Interest cost 1,550 1,335 3,101 2,670
Expected return on plan assets (2,580) (2,307) (5,161) (4,614)
Amortization of Unrecognized actuarial net loss 430 598 859 1,196
Amortization of Unrecognized prior service cost (credit) 0 0 0 0
Amortization of Curtailment 0 0 0 0
Net periodic benefit cost (credit) (600) (374) (1,201) (748)
Other Postemployment Benefits
        
Defined Benefit Plan Disclosure [Line Items]        
Service cost 153 224 306 473
Interest cost 374 349 749 711
Expected return on plan assets 0 0 0 0
Amortization of Unrecognized actuarial net loss 21 45 43 103
Amortization of Unrecognized prior service cost (credit) (286) (111) (573) (174)
Amortization of Curtailment 0 (116) 0 (116)
Net periodic benefit cost (credit) $ 262 $ 391 $ 525 $ 997