Share-Based Compensation - Expense Table (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
Stock Options Compensation Expense [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based Compensation Expense	958	848	730
Nonvested Stock Awards Compensation Expense [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based Compensation Expense	2,935	3,121	2,937
Employee Stock Purchase Plan Compensation Expense [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based Compensation Expense	88	87	75
Matching Stock Contribution 401 K Plan Compensation Expense [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based Compensation Expense	72	2,124	2,052
Directors Stock Ownership Plan Compensation Expense [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based Compensation Expense	$ 137	$ 169	$ 125