Postretirement Benefits (Details 10) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair value measurements of pension plan assets:
Total	$ 551,491	$ 547,788	$ 462,322
Employee pension plan
Fair value measurements of pension plan assets:
Total	551,491	547,788
Employee pension plan | Level 1
Fair value measurements of pension plan assets:
Total	5,906	3,325
Employee pension plan | Level 2
Fair value measurements of pension plan assets:
Total	545,585	544,463
Employee pension plan | Level 3
Fair value measurements of pension plan assets:
Total	0	0
Employee pension plan | Total equity securities
Fair value measurements of pension plan assets:
Total	308,966	308,061
Employee pension plan | Total equity securities | Level 1
Fair value measurements of pension plan assets:
Total	0	0
Employee pension plan | Total equity securities | Level 2
Fair value measurements of pension plan assets:
Total	308,966	308,061
Employee pension plan | Total equity securities | Level 3
Fair value measurements of pension plan assets:
Total	0	0
Employee pension plan | U.S. equity securities
Fair value measurements of pension plan assets:
Total	201,021	202,036
Employee pension plan | U.S. equity securities | Level 1
Fair value measurements of pension plan assets:
Total	0	0
Employee pension plan | U.S. equity securities | Level 2
Fair value measurements of pension plan assets:
Total	201,021	202,036
Employee pension plan | U.S. equity securities | Level 3
Fair value measurements of pension plan assets:
Total	0	0
Employee pension plan | Non-U.S. equity securities
Fair value measurements of pension plan assets:
Total	107,945	106,025
Employee pension plan | Non-U.S. equity securities | Level 1
Fair value measurements of pension plan assets:
Total	0	0
Employee pension plan | Non-U.S. equity securities | Level 2
Fair value measurements of pension plan assets:
Total	107,945	106,025
Employee pension plan | Non-U.S. equity securities | Level 3
Fair value measurements of pension plan assets:
Total	0	0
Employee pension plan | Debt securities
Fair value measurements of pension plan assets:
Total	236,619	236,402
Employee pension plan | Debt securities | Level 1
Fair value measurements of pension plan assets:
Total	0	0
Employee pension plan | Debt securities | Level 2
Fair value measurements of pension plan assets:
Total	236,619	236,402
Employee pension plan | Debt securities | Level 3
Fair value measurements of pension plan assets:
Total	0	0
Employee pension plan | Other
Fair value measurements of pension plan assets:
Total	5,906	3,325
Employee pension plan | Other | Level 1
Fair value measurements of pension plan assets:
Total	5,906	3,325
Employee pension plan | Other | Level 2
Fair value measurements of pension plan assets:
Total	0	0
Employee pension plan | Other | Level 3
Fair value measurements of pension plan assets:
Total	$ 0	$ 0