Pension, Savings, and Other Employee Benefits - Schedule of Benefit Obligation and Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in benefit obligation
Plan Amendments	$ 0	$ 0
Premium paid for annuity purchase		0
Change in plan assets
Premium paid for annuity purchase		0
Pension Benefits
Change in benefit obligation
Benefit obligation, beginning of year	765,309	840,884
Service cost	30	41	$ 37
Interest cost	30,207	27,877	29,380
Actuarial (gain)/loss	102,775	(68,724)
Actual benefits paid	(38,450)	(34,769)
Premium paid for annuity purchase	(23,997)
Benefit obligation, end of year	835,874	765,309	840,884
Change in plan assets
Fair value of plan assets, beginning of year	730,953	811,244
Actual return on plan assets	154,054	(49,470)
Employer contributions	3,510	3,948
Actual benefits paid – settlement payments	0	0
Actual benefits paid – other payments	(38,450)	(34,769)
Premium paid for annuity purchase	(23,997)
Fair value of plan assets, end of year	826,070	730,953	811,244
Funded (unfunded) status of the plans	(9,804)	(34,356)
Amounts recognized in the Statements of Condition
Other assets	27,433	1,911
Other liabilities	(37,237)	(36,267)
Net asset/(liability) at end of year	(9,804)	(34,356)
Other Benefits
Change in benefit obligation
Benefit obligation, beginning of year	35,174	39,562
Service cost	94	133	107
Interest cost	1,413	1,309	1,305
Plan Amendments	408
Actuarial (gain)/loss	6,848	(3,648)
Actual benefits paid	(1,641)	(2,182)
Premium paid for annuity purchase	0	0
Benefit obligation, end of year	42,296	35,174	39,562
Change in plan assets
Fair value of plan assets, beginning of year	17,432	18,753
Actual return on plan assets	3,355	(928)
Employer contributions	1,259	1,789
Actual benefits paid – settlement payments	(1,641)	(2,182)
Actual benefits paid – other payments	0	0
Premium paid for annuity purchase	0	0
Fair value of plan assets, end of year	20,405	17,432	$ 18,753
Funded (unfunded) status of the plans	(21,891)	(17,742)
Amounts recognized in the Statements of Condition
Other assets	17,240	14,356
Other liabilities	(39,131)	(32,098)
Net asset/(liability) at end of year	$ (21,891)	$ (17,742)