SERP Expense and Contributions paid (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Retirement expense	$ 1,100	$ 1,900	$ 2,000
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Retirement expense	1,683	1,580	1,513
Contributions paid	$ 434	$ 367	$ 320