Employee Benefit Plans - Net Pension Cost (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Components of net pension cost
Net periodic pension cost for the three and nine months ended September 30, (actual)		$ 379	$ 405
Pension Benefits
Components of net pension cost
Service cost - benefits earned during the year		1,516	1,707
Interest costs on projected benefit obligations	[1]	1,168	1,037
Expected return on plan assets	[1]	(1,393)	(1,327)
Expected administrative expenses	[1]	100	93
Amortization of prior service cost	[1]	79	79
Amortization of unrecognized net loss	[1]	0	140
Net periodic pension cost		1,470	1,729
Net periodic pension cost for the three and nine months ended September 30, (actual)		$ 379	$ 405

[1] The components of net periodic pension cost other than the service cost component are included in other non-interest expense.