Stock Option Plans (Summary of Status and Changes in Stock Option Plan) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares
Options outstanding, Beginning balance	304,561
Options granted	0	0	0
Options exercised	65,161	77,600	186,059
Options outstanding, Ending balance	239,400	304,561
Weighted Average Exercise Price
Options Outstanding, Weighted Average Exercise Price, Beginning balance	$ 9.90
Options Exercised, Weighted Average Exercise Price	17.73
Options Outstanding, Weighted Average Exercise Price, Ending balance	$ 7.78	$ 9.90
Weighted- Average Remaining Contractual Life (in years)
Options Outstanding, Weighted-Average Remaining Contractual Life	7 years 7 months 6 days
Aggregate Intrinsic Value
Options Outstanding, Aggregate Intrinsic Value	$ 7,236