Stock Option Plans (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Options exercised	65,161	77,600	186,059
Proceeds from stock options exercised	$ 1,200,000	$ 976,000	$ 2,000,000
Options exercised during the period, intrinsic value	$ 1,100,000	$ 911,000	$ 2,200,000
Options granted	0	0	0
2000 Stock Option Plan [Member]
Shares authorized to grant options	141,462
Options granted	0	0
Equity Compensation Plan [Member]
Shares authorized to grant options	352,741
Shares remaining to be granted under plan	58,003