Employee Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Pension Plan
Net periodic benefit cost
Service cost	$ 1,997	$ 2,175	$ 5,991	$ 6,525
Interest cost	2,080	1,875	6,240	5,625
Expected return on plan assets	(2,696)	(2,626)	(8,088)	(7,877)
Amortization of prior service credit	0	0	0	0
Amortization of net loss	901	1,072	2,703	3,215
Net periodic benefit cost	2,282	2,496	6,846	7,488
Estimated 2019 pension plan contribution, disclosed in prior year 10K					$ 4,000
Contribution by employer			4,000
Postretirement Benefit Plan
Net periodic benefit cost
Service cost	456	750	1,368	2,249
Interest cost	319	502	956	1,506
Expected return on plan assets	0	0	0	0
Amortization of prior service credit	(2,221)	(1,352)	(6,463)	(4,056)
Amortization of net loss	224	589	671	1,767
Net periodic benefit cost	$ (1,222)	$ 489	$ (3,468)	$ 1,466