Share-Based Compensation - Option Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based Compensation Expense	$ 4,190	$ 6,349	$ 5,919
Current Year Stock Option Awards [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based Compensation Expense	308	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	332	282	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	276	276	232
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	$ 42	$ 254	$ 257