Pensions and Other Postemployment Benefits (OPEB) - Components of Net Periodic Benefit Cost (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Jun. 30, 2013
Sep. 30, 2014
Sep. 30, 2013
Pension Benefits
         
Defined Benefit Plan Disclosure [Line Items]          
Service cost $ 0 $ 0   $ 0 $ 0
Interest cost 1,551 1,335   4,652 4,005
Expected return on plan assets (2,582) (2,307)   (7,743) (6,921)
Amortization of Unrecognized actuarial net loss 430 598   1,289 1,794
Amortization of Unrecognized prior service cost (credit) 0 0   0 0
Amortization of Curtailment       0 0
Net periodic benefit cost (credit) (601) (374)   (1,802) (1,122)
Other Postemployment Benefits
         
Defined Benefit Plan Disclosure [Line Items]          
Service cost 153 157   459 630
Interest cost 375 329   1,124 1,040
Expected return on plan assets 0 0   0 0
Amortization of Unrecognized actuarial net loss 22 0   65 103
Amortization of Unrecognized prior service cost (credit) (287) (289)   (860) (463)
Amortization of Curtailment     (100) 0 (116)
Net periodic benefit cost (credit) $ 263 $ 197   $ 788 $ 1,194