Employee Benefit Plans - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Defined pension plan benefits
Defined Benefit Plan Disclosure [Line Items]
Settlement expense	$ (11,732)	$ (8,200)	$ 0	$ (19,900)	$ 0
Benefits paid	1,300	$ 1,600
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Settlement expense	$ 0		$ 0	0	$ 0
Benefits paid				$ 234
Estimated other postretirement benefits to be paid in 2017						$ 400