Retirement Plans - Summary of Categories in Fair Value Hierarchy (Details 9) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	$ 259,752	$ 286,539
Equity Securities | U.S.
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	20,469	19,487
Equity Securities | non-U.S.
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	0	1,131
Equity Funds
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	54	1,314
Equity Funds | International LP
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount		1,314
Bond funds - government
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	19,146	3,126
Bond funds - other
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	202,393	231,710
Real estate
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	2,652	1,235
Cash and Cash Equivalents
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	5,866	11,145
Partnership
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	9,172	10,787
International hedge funds
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	0	6,604
Quoted Prices in Active Markets (Level 1)
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	26,335	31,763
Quoted Prices in Active Markets (Level 1) | Equity Securities | U.S.
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	20,469	19,487
Quoted Prices in Active Markets (Level 1) | Equity Securities | non-U.S.
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount		1,131
Quoted Prices in Active Markets (Level 1) | Cash and Cash Equivalents
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	5,866	11,145
Significant Other Observable Inputs (Level 2)
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	0	0
Significant Other Observable Inputs (Level 2) | Equity Securities | non-U.S.
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount		0
Significant Other Observable Inputs (Level 2) | Equity Funds
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	0
Significant Other Observable Inputs (Level 2) | Equity Funds | International LP
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount		0
Significant Other Observable Inputs (Level 2) | Bond funds - government
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	0	0
Significant Other Observable Inputs (Level 2) | Bond funds - other
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	0	0
Significant Other Observable Inputs (Level 2) | Real estate
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	9,172	10,787
Significant Unobservable Inputs (Level 3) | Partnership
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount	$ 9,172	10,787	$ 12,862
Significant Unobservable Inputs (Level 3) | International hedge funds
Fair values of pension plan assets
Defined Benefit Plan, Plan Assets, Amount		$ 0