Benefit Plans - Change in Net Actuarial Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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	$ 45,579	$ 59,811
Amortization cost	(7,629)	(9,928)	$ (5,163)
Liability loss (gain)	9,653	(8,004)	35,083
Asset loss	3,350	3,700	(1,677)
Change due to the Reorganization Transactions	81
Net actuarial loss at end of year	51,034	45,579	59,811
Other Benefits
Change in net actuarial loss and amortization
Net actuarial loss at beginning of year	619	1,669
Amortization cost		(32)
Liability loss (gain)	(337)	(1,018)	1,471
Net actuarial loss at end of year	$ 282	$ 619	$ 1,669