Employee Benefit Plans - Net Pension 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 net pension cost
Net periodic pension cost for the three and six months ended June 30, (actual)		$ 336	$ 405	$ 715	$ 810
Pension Benefits
Components of net pension cost
Service cost - benefits earned during the year				1,431	1,707
Interest costs on projected benefit obligations	[1]			1,168	1,037
Expected return on plan assets	[1]			(1,467)	(1,327)
Expected administrative expenses	[1]			122	93
Amortization of prior service cost	[1]			79	79
Amortization of unrecognized net loss	[1]			0	140
Net periodic pension cost				1,333	1,729
Net periodic pension cost for the three and six months ended June 30, (actual)		$ 336	$ 405	$ 715	$ 810

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