Employee Retirement and Postretirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plans
Components of net periodic benefit cost:
Service cost	$ 672	$ 732	$ 2,016	$ 2,196
Interest cost	3,084	2,828	9,252	8,484
Expected return on plan assets	(3,996)	(4,411)	(11,988)	(13,233)
Amortizations:
Prior service cost	108	108	324	324
Unrecognized net loss	2,440	2,130	7,320	6,390
Net periodic benefit cost	2,308	1,387	6,924	4,161
Postretirement Benefits
Components of net periodic benefit cost:
Service cost	154	170	462	510
Interest cost	281	235	843	705
Amortizations:
Prior service cost	23	23	69	69
Unrecognized net loss	(151)	(118)	(453)	(354)
Net periodic benefit cost	$ 307	$ 310	$ 921	$ 930