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Retirement and Benefit Plans (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Pension contributions [Abstract]    
Pension contributions $ 630 $ 2,340
Estimated remaining 2017 contributions 1,600  
Pension Plan [Member]    
Net periodic benefit cost [Abstract]    
Service cost 301 285
Interest cost 4,376 4,782
Expected return on plan assets (4,740) (5,103)
Amortization of actuarial loss 395 478
Plan settlement loss 0 297
Net periodic benefit expense $ 332 $ 739