Pension and Employee Benefit Plans - Changes in obligations and plan assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in plan assets, at fair value
Beginning plan assets	$ 12,595
Plan assets - end of year		$ 12,595
Modified Retirement Plan | Unfunded Plan
Accumulated benefit obligation:
Accumulated benefit obligation - beginning of year	21,736	21,705
Service cost	392	363	$ 551
Interest cost	931	801	778
Plan amendments	386	412
Actuarial (gains) losses	2,390	(949)
Benefits paid	(730)	(596)
Accumulated benefit obligation - end of year	25,105	21,736	21,705
Change in plan assets, at fair value
Beginning plan assets	0	0
Actual return	0	0
Employer contribution	730	596
Benefits paid	(730)	(596)
Plan assets - end of year	0	0	0
Funded status - end of year (plan assets less benefit obligations)	(25,105)	(21,736)
Funded Plan | Funded Plan
Accumulated benefit obligation:
Accumulated benefit obligation - beginning of year	16,011	17,700
Service cost	0	0	0
Interest cost	166	647	738
Plan amendments	0	0
Actuarial (gains) losses	1,489	(839)
Benefits paid	(17,666)	(1,497)
Accumulated benefit obligation - end of year	0	16,011	17,700
Change in plan assets, at fair value
Beginning plan assets	12,595	14,308
Actual return	173	(216)
Employer contribution	4,898	0
Benefits paid	(17,666)	(1,497)
Plan assets - end of year	0	12,595	$ 14,308
Funded status - end of year (plan assets less benefit obligations)	$ 0	$ (3,416)