Short-Term Borrowings and Long-Term Debt (Schedule of Maturities of Long-term Debt) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Due in 2018	$ 35,000	$ 20,000
Due in 2019		25,000
Due in 2020	10,000
Due in 2021		10,000
Due in 2022	10,302
Thereafter	196	10,559
Long-term debt, total	55,498	65,559	$ 55,617
Fixed Rate [Member]
Debt Instrument [Line Items]
Due in 2018	25,000	20,000
Due in 2019		15,000
Due in 2022	10,302
Thereafter	196	10,559
Long-term debt, total	35,498	45,559
Fixed Rate Convertible [Member]
Debt Instrument [Line Items]
Due in 2018	10,000
Due in 2019		10,000
Long-term debt, total	10,000	10,000
Variable Rate [Member]
Debt Instrument [Line Items]
Due in 2020	10,000
Due in 2021		10,000
Long-term debt, total	$ 10,000	$ 10,000