Benefit Plans - Change in Net Actuarial Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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 (gain) at beginning of year	$ 41,822	$ 43,547
Amortization cost	(6,995)	(7,315)	$ (8,625)
Liability loss (gain)	21,512	(6,619)	9,757
Asset (gain) loss	(16,278)	12,209	(8,619)
Net actuarial loss (gain) at end of year	40,061	41,822	43,547
Other Benefits
Change in net actuarial loss and amortization
Net actuarial loss (gain) at beginning of year	(2,507)	248
Amortization cost	385
Liability loss (gain)	540	(2,755)	(34)
Net actuarial loss (gain) at end of year	$ (1,582)	$ (2,507)	$ 248