Retirement Plans - Net Periodic Benefit Plan (Income) Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Pension Plans
Net periodic benefit plan (income) cost included in non-interest expense
Interest cost	$ 1,046	$ 246	$ 1,574	$ 738
Service cost	0	0	0	0
Contractual termination cost	0	0	0	0
Return on plan assets	(949)	(133)	(1,223)	(397)
Amortization of prior service credit	0	0	0	0
Amortization of unrecognized net loss	0	0	0	0
Recognized actuarial (gain) loss			0	0
Net periodic benefit plan (income) cost	97	113	351	341
Postretirement Benefit Plans
Net periodic benefit plan (income) cost included in non-interest expense
Interest cost	41	28	101	83
Service cost	0	0	0	0
Amortization of prior service credit	(11)	(12)	(35)	(35)
Amortization of unrecognized net loss	0	0	0	0
Recognized actuarial (gain) loss	0	0	0	0
Net periodic benefit plan (income) cost	$ 30	$ 16	$ 66	$ 48