Pension Plan and Employee Benefits - Projected Benefit Payments and Projected Receipts (Details) $ in Thousands	Dec. 31, 2018 USD ($)
PENSION BENEFITS
For the year ending Dec. 31,
2019	$ 22,868
2020	24,042
2021	25,180
2022	26,373
2023	27,512
Next five years	154,047
OTHER BENEFITS
For the year ending Dec. 31,
2019	4,215
2020	4,071
2021	3,936
2022	3,856
2023	3,716
Next five years	16,615
SERP BENEFITS
For the year ending Dec. 31,
2019	4,574
2020	4,670
2021	4,755
2022	4,754
2023	4,755
Next five years	$ 24,717