Employee Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Pension Plan
Net periodic benefit cost
Service cost	$ 1,997	$ 2,175
Interest cost	2,080	1,875
Expected return on plan assets	(2,696)	(2,625)
Amortization of prior service credit	0	0
Amortization of net loss	901	1,071
Net periodic benefit cost	2,282	2,496
Estimated 2019 pension plan contribution, disclosed in prior year 10K			$ 4,000
Contribution by employer	1,000
Postretirement Benefit Plan
Net periodic benefit cost
Service cost	456	749
Interest cost	319	502
Expected return on plan assets	0	0
Amortization of prior service credit	(2,021)	(1,352)
Amortization of net loss	223	589
Net periodic benefit cost	$ (1,023)	$ 488