Retirement Plans Retirement Plans Level 4 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used in Calculation, Description	0.5
Defined Benefit Plan, Interest Cost	$ 1,067	$ 1,179	$ 1,198
Defined Benefit Plan, Amortization of Gain (Loss)	879	259	(1,327)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	1,946	1,438	(129)
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation	30,078	32,305
Defined Benefit Plan, Interest Cost	1,067	1,179	1,198
Defined Benefit Plan, Actuarial Net (Gains) Losses	879	259
Defined Benefit Plan, Benefit Obligation, Benefits Paid	3,343	3,665
Defined Benefit Plan, Benefit Obligation	28,681	30,078	32,305
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Defined Benefit Plan, Plan Assets, Contributions by Employer	3,343	3,665
Defined Benefit Plan, Fair Value of Plan Assets	0	0	$ 0
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(28,681)	(30,078)
Defined Benefit Plan, Accumulated Benefit Obligation	28,681	30,078
Liability, Defined Benefit Pension Plan, Current	(3,265)	(3,448)
Liability, Defined Benefit Pension Plan, Noncurrent	(25,416)	(26,630)
Liability, Defined Benefit Pension Plan	(28,681)	(30,078)
Defined Benefit Plan, Estimated Future Retirement Benefits Covered by Insurance Contract, Amount	46,500	47,500
Cash Surrender Value of Life Insurance, Retirement Plans	$ 36,400	$ 37,000
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.41%	3.76%	3.86%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	3.86%	3.96%	2.47%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase	0.00%
Year One	$ 3,265
Year Two	3,192
Year Three	2,760
Year Four	2,447
Year Five	2,369
Years 2023 through 2027	9,379
Defined Contribution Plan, Cost	33,200	$ 32,500	$ 30,800
Defined Benefit Plan, Plan Assets, Benefits Paid	$ 3,343	$ 3,665