Pension and Other Post Retirement Benefit Plans - Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Net periodic pension benefit cost	$ (1,693)	$ 654	$ 509
Amortization of net loss	(2,189)	1,504	(228)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Amortization Cost (Credit), before Tax	287	1,979	1,656
Amortization of prior service cost	87	90	79
Total recognized in other comprehensive income (loss)	(1,815)	3,573	1,507
Total recognized in net periodic pension benefit cost and other comprehensive income (loss)	$ (122)	$ 2,919	$ 998