Employer Sponsored Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Components of employer benefit cost
Service cost	$ 30	$ 0	$ 60	$ 0
Interest cost	833	470	1,827	940
Expected return on assets	(744)	(650)	(1,616)	(1,300)
Amortization of actuarial loss	186	256	464	512
Total employer benefit plan cost	305	76	735	152
Settlement loss	25,515	0	25,515	0
Total employer benefit plan cost	$ 25,820	$ 76	$ 26,250	$ 152