Benefit Plans - (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Components of net periodic benefit cost
Service cost	$ 132	$ 98	$ 396	$ 294
Interest cost	60	59	180	177
Expected return on assets	(122)	(117)	(366)	(351)
Amortization of prior service cost and net loss	45	13	135	39
Pension expense	$ 115	$ 53	$ 345	$ 159