Retirement Plans-Net Periodic Benefit Costs and Benefit Payments (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
|
| Defined Benefit Plan, Net Periodic Benefit Cost [Abstract] | |||
| Service cost | $ 1,698 | $ 2,667 | |
| Interest cost | 32,655 | 35,269 | |
| Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract] | |||
| 2016 | 43,644 | ||
| 2017 | 44,364 | ||
| 2018 | 44,965 | ||
| 2019 | 45,548 | ||
| 2020 | 46,043 | ||
| 2021-2025 | 233,183 | ||
| Retirement liabilities | |||
| Defined Benefit Plan, Net Periodic Benefit Cost [Abstract] | |||
| Service cost | 1,698 | 2,667 | $ 2,922 |
| Interest cost | 32,655 | 35,270 | 33,309 |
| Expected return on assets | (41,710) | (45,481) | (42,949) |
| Amortization of actuarial loss | 13,371 | 11,828 | 13,263 |
| Net periodic benefit cost | $ 6,014 | $ 4,284 | $ 6,545 |