Postretirement Benefits (Details 10) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair value measurements of pension plan assets:
Total	$ 592,544	$ 551,491	$ 547,788
Employee pension plan
Fair value measurements of pension plan assets:
Total	592,544	551,491
Employee pension plan | Level 1
Fair value measurements of pension plan assets:
Total	5,948	5,906
Employee pension plan | Level 2
Fair value measurements of pension plan assets:
Total	586,596	545,585
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	333,399	308,966
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	333,399	308,966
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	225,446	201,021
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	225,446	201,021
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	107,953	107,945
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	107,953	107,945
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	253,197	236,619
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	253,197	236,619
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	5,948	5,906
Employee pension plan | Other | Level 1
Fair value measurements of pension plan assets:
Total	5,948	5,906
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