Employee Benefit Plans - Net Pension Cost (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Components of net pension cost
Net periodic pension cost for the three months ended March 31, (actual)		$ 464	$ 379
Pension Benefits
Components of net pension cost
Service cost - benefits earned during the year		1,857	1,516
Interest costs on projected benefit obligations	[1]	1,159	1,168
Expected return on plan assets	[1]	(1,572)	(1,393)
Expected administrative expenses	[1]	110	100
Amortization of prior service cost	[1]	50	79
Amortization of unrecognized net loss	[1]	218	0
Net periodic pension cost		1,822	1,470
Net periodic pension cost for the three months ended March 31, (actual)		$ 464	$ 379

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