Share-Based Compensation - Option Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based Compensation Expense	$ 3,724	$ 4,190	$ 6,349
Current Year Stock Option Awards [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based Compensation Expense	310	0	0
Unrecognized Compensation Expense, Options	800
Prior Year Stock Option Awards [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based Compensation Expense	367	308	0
Unrecognized Compensation Expense, Options	400
Second Prior Year Stock Option Awards [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based Compensation Expense	332	332	282
Unrecognized Compensation Expense, Options	100
Third Prior Year Stock Option Awards [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based Compensation Expense	$ 44	$ 276	$ 276