Retirement Plans, Fair Value of Pension Plan Investments Table (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Pension Plan Investments
Money market account	$ 9,577	$ 3,624
Common /collective trust funds	133,210	126,741
Mutual funds	188,823	165,353
Total Retirement Account Plan Investments	331,610	295,718
Fair Value, Inputs, Level 1
Pension Plan Investments
Money market account	9,577	3,624
Common /collective trust funds	133,210	126,741
Mutual funds	188,823	165,353
Total Retirement Account Plan Investments	331,610	295,718
Fair Value, Inputs, Level 2
Pension Plan Investments
Money market account	0	0
Common /collective trust funds	0	0
Mutual funds	0	0
Total Retirement Account Plan Investments	0	0
Fair Value, Inputs, Level 3
Pension Plan Investments
Money market account	0	0
Common /collective trust funds	0	0
Mutual funds	0	0
Total Retirement Account Plan Investments	$ 0	$ 0