Pension and Employee Benefit Plans - Changes in obligations and plan assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in plan assets, at fair value
Beginning plan assets	$ 14,308
Plan assets - end of year	12,595	$ 14,308
Modified Retirement Plan | Unfunded Plan
Accumulated benefit obligation:
Accumulated benefit obligation - beginning of year	21,705	19,408
Service cost	363	551	$ 382
Interest cost	801	778	740
Plan amendments	412	699
Actuarial (gains) losses	(949)	773
Benefits paid	(596)	(504)
Accumulated benefit obligation - end of year	21,736	21,705	19,408
Change in plan assets, at fair value
Beginning plan assets	0	0
Actual return	0	0
Employer contribution	596	504
Benefits paid	(596)	(504)
Plan assets - end of year	0	0	0
Funded status - end of year (plan assets less benefit obligations)	(21,736)	(21,705)
Funded Plan | Funded Plan
Accumulated benefit obligation:
Accumulated benefit obligation - beginning of year	17,700	18,501
Service cost	0	0	0
Interest cost	647	738	842
Plan amendments	0	0
Actuarial (gains) losses	(839)	1,291
Benefits paid	(1,497)	(2,830)
Accumulated benefit obligation - end of year	16,011	17,700	18,501
Change in plan assets, at fair value
Beginning plan assets	14,308	16,264
Actual return	(216)	874
Employer contribution	0	0
Benefits paid	(1,497)	(2,830)
Plan assets - end of year	12,595	14,308	$ 16,264
Funded status - end of year (plan assets less benefit obligations)	$ (3,416)	$ (3,392)