Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Components of Net Periodic Benefit Cost
Service cost	$ 300	$ 300	$ 749	$ 900	$ 1,200
Interest cost	348	310	1,045	931	$ 1,242
Net loss	53	133	158	399
Net periodic pension cost	$ 701	$ 743	$ 1,952	$ 2,230