Employee Benefit Plans Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost (1)	$ 0	$ 688	$ 579
Interest cost	3,320	3,520	3,405
Expected return on assets	(1,804)	(2,318)	(3,009)
Net amortization and deferral	2,652	2,420	3,127
Net periodic benefit cost	4,168	4,310	4,102
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Interest cost	68	85	206
Net amortization and deferral	(565)	(551)	(258)
Net periodic benefit cost	$ (497)	$ (466)	$ (52)