Net Income Per Share Computations (Narrative) (Details) - $ / shares	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Number of common stock shares to purchase under stock options	191,002	223,002	255,252
Average price of common shares under stock options	$ 9.08	$ 9.30	$ 9.63
Excluded From Diluted Net Income Computation [Member]
Number of common stock shares to purchase under stock options	45,000	75,000
Average price of common shares under stock options	$ 12.80	$ 13.45