Employee Benefit Plans - Funded status of Retirement Income Plan and amounts recognized in consolidated balance sheets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation at end of year	$ 48,519	$ 43,417
Retirement Income Plan
CHANGE IN PROJECTED BENEFIT OBLIGATION:
Benefit obligation at beginning of year	43,417	46,397
Service cost	0	0	$ 0
Interest cost	1,960	1,832	1,932
Amendments	0	0
Actuarial loss (gain)	5,521	(2,658)
Benefits paid	(2,379)	(2,154)
Projected benefit obligation at end of year	48,519	43,417	46,397
CHANGE IN PLAN ASSETS:
Fair value of plan assets at beginning of year	38,364	38,050
Actual return (loss) on plan assets	4,157	(2,532)
Employer contribution	0	5,000
Benefits paid	(2,379)	(2,154)
Fair value of plan assets at end of year	40,142	38,364	38,050
Funded status at end of year	(8,377)	(5,053)
AMOUNTS (PRE-TAX) RECOGNIZED IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) CONSIST OF:
Net loss	27,693	24,650
Prior service cost (credit)	0	0
Net transition obligation (asset)	0	0	$ 0
Before-tax amount	$ 27,693	$ 24,650