Retirement Plans - Summary of Fair Values of Pension Plan (Details 8) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair values of pension plan assets
Total fair value of plan assets	$ 259,752	$ 286,539
Equity Securities | U.S.
Fair values of pension plan assets
Total fair value of plan assets	20,469	19,487
Equity Securities | non-U.S.
Fair values of pension plan assets
Total fair value of plan assets	0	1,131
Equity Funds
Fair values of pension plan assets
Total fair value of plan assets	54	1,314
Equity Funds | International LP
Fair values of pension plan assets
Total fair value of plan assets		1,314
Bond funds - government
Fair values of pension plan assets
Total fair value of plan assets	19,146	3,126
Bond funds - other
Fair values of pension plan assets
Total fair value of plan assets	202,393	231,710
Real estate
Fair values of pension plan assets
Total fair value of plan assets	2,652	1,235
Cash and Cash Equivalents
Fair values of pension plan assets
Total fair value of plan assets	5,866	11,145
Partnership
Fair values of pension plan assets
Total fair value of plan assets	9,172	10,787
International hedge funds
Fair values of pension plan assets
Total fair value of plan assets	$ 0	$ 6,604