Retirement Plans- Projected Benefit Obligations and Fair Value of Plan Assets (Details) - USD ($) $ in Thousands |
Dec. 31, 2015 |
Dec. 31, 2014 |
|---|---|---|
| Plans with PBO in Excess of Plan Assets [Abstract] | ||
| Projected benefit obligations | $ 538,507 | $ 806,269 |
| Fair value of plans' assets | 413,204 | 659,875 |
| Plans with Plan Assets in Excess of Benefit Obligations [Abstract] | ||
| Projected benefit obligations | 261,186 | 62,478 |
| Fair value of plans' assets | $ 276,295 | $ 65,895 |