Retirement Plans - Summary of Categories in Fair Value Hierarchy (Details 9) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	$ 282,696	$ 259,752
Equity Securities
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	24,586	20,469
Equity Funds
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	0	54
Bond funds - government
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	33,991	19,146
Bond funds - other
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	207,901	202,393
Real estate
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	2,979	2,652
Cash and Cash Equivalents
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	5,700	5,866
Partnership
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	7,539	9,172
Quoted Prices in Active Markets (Level 1)
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	30,286	26,335
Quoted Prices in Active Markets (Level 1) | Equity Securities
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	24,586	20,469
Quoted Prices in Active Markets (Level 1) | Cash and Cash Equivalents
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	5,700	5,866
Significant Other Observable Inputs (Level 2)
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	0	0
Significant Unobservable Inputs (Level 3)
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	7,539	9,172
Significant Unobservable Inputs (Level 3) | Partnership
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	7,539	9,172	$ 10,787
UNITED STATES
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	281,276	258,327	284,762
Foreign Plan
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	$ 1,419	$ 1,425	$ 1,777