Pension and Postretirement Benefit Plans - Changes in Benefit Obligations and Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SERP I and SERP II
Change in benefit obligations
Benefit obligation at January 1	$ 4,983	$ 4,786
Service cost	0	0	$ 0
Interest cost	160	176	184
Plan participants contribution	0	0
Actuarial loss (gain)	(180)	282
Settlements	0	0
Benefits paid	(276)	(261)
Benefit obligation at December 31	4,687	4,983	4,786
Change in plan assets
Fair value of plan assets at January 1	0	0
Actual return on plan assets	0	0
Settlements	0	0
Excess assets transferred to defined contribution plan	0	0
Employer contribution	278	261
Plan participants’ contribution	0	0
Benefits paid	(278)	(261)
Fair value of plan assets at December 31	0	0	0
Funded status at year end (plan assets less benefit obligations)	(4,687)	(4,983)
Accrued liability	(3,174)	(3,221)
Net actuarial loss	(1,513)	(1,762)
PRBP
Change in benefit obligations
Benefit obligation at January 1	353	418
Service cost	0	0	0
Interest cost	9	11	17
Plan participants contribution	44	44
Actuarial loss (gain)	(61)	(9)
Settlements	0	0
Benefits paid	(104)	(111)
Benefit obligation at December 31	241	353	418
Change in plan assets
Fair value of plan assets at January 1	0	0
Actual return on plan assets	0	0
Settlements	0	0
Excess assets transferred to defined contribution plan	0	0
Employer contribution	60	67
Plan participants’ contribution	44	44
Benefits paid	(104)	(111)
Fair value of plan assets at December 31	0	0	$ 0
Funded status at year end (plan assets less benefit obligations)	(241)	(353)
Accrued liability	(129)	(149)
Net actuarial loss	$ (112)	$ (204)