Benefit Plans - Amounts Recognized in Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits
Amounts arising during the year:
Net loss (gain) on pension assets	$ 12,209	$ (8,619)	$ 3,350
Net loss (gain) on pension obligations	(6,619)	9,757	9,653
Change due to the Reorganization Transactions			81
Reclassification adjustments recognized as components of net periodic benefit cost during the year:
Net loss	(7,315)	(8,625)	(7,629)
Amount recognized in other comprehensive income	(1,725)	(7,487)	5,455
Other Benefits
Amounts arising during the year:
Net loss (gain) on pension obligations	(2,755)	(34)	(337)
Reclassification adjustments recognized as components of net periodic benefit cost during the year:
Prior service credit	429	429	429
Amount recognized in other comprehensive income	$ (2,326)	$ 395	$ 92