Employee Benefit Plans - Net Pension Cost (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Components of net pension cost
Net periodic pension cost for the three and six months ended june 30		$ 343	$ 336	$ 807	$ 715
Pension Benefits
Components of net pension cost
Service cost - benefits earned during the year				1,614	1,431
Interest costs on projected benefit obligations	[1]			1,127	1,168
Expected return on plan assets	[1]			(1,598)	(1,467)
Expected administrative expenses	[1]			110	122
Amortization of prior service cost	[1]			50	79
Amortization of unrecognized net loss	[1]			164	0
Net periodic pension cost				1,467	1,333
Net periodic pension cost for the three and six months ended june 30		$ 343	$ 336	$ 807	$ 715

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