Benefit Plans - Change in Net Actuarial Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Benefit plans
Percentage of greater of projected benefit obligation or fair value of plan assets for amortization of actuarial gains or losses	5.00%
Amortization period for actuarial gains and losses that exceed threshold	5 years
Pension Benefits
Change in net actuarial loss and amortization
Net actuarial loss at beginning of year	$ 43,547	$ 51,034
Amortization cost	(7,315)	(8,625)	$ (7,629)
Liability loss (gain)	(6,619)	9,757	9,653
Asset (gain) loss	12,209	(8,619)	3,350
Change due to the Reorganization Transactions			81
Net actuarial loss at end of year	41,822	43,547	51,034
Other Benefits
Change in net actuarial loss and amortization
Net actuarial loss at beginning of year	248	282
Liability loss (gain)	(2,755)	(34)	(337)
Net actuarial loss at end of year	$ (2,507)	$ 248	$ 282