Stock-Based Compensation Plan (Summary Of Stock Option Activities) (Details) - Stock Options [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding at beginning of period, Number of Shares	1,428,255	1,189,255	1,420,749
Options granted, Number of Shares	230,500	245,000	183,000
Options exercised, Number of Shares	(799,195)		(414,494)
Options forfeited/cancelled, Number of Shares		(6,000)
Options outstanding at end of period, Number of Shares	859,560	1,428,255	1,189,255
Options exercisable, Number of Shares	443,689
Expected to vest after end of period, Number of Shares	415,871
Options outstanding at beginning of period, Weighted Average Exercise Price	$ 16.31	$ 18.08	$ 15.67
Options granted, Weighted Average Exercise Price	16.80	7.87	21.72
Options exercised, Weighted Average Exercise Price	16.31		11.45
Options forfeited/cancelled, Weighted Average Exercise Price		21.99
Options outstanding at end of period, Weighted Average Exercise Price	16.44	$ 16.31	$ 18.08
Options exercisable, Weighted Average Exercise Price	17.85
Expected to vest after end of period, Weighted Average Exercise Price	$ 14.94
Weighted average remaining term	7 years 2 months 12 days
Weighted average remaining term	5 years 10 months 24 days
Expected to vest after end of period, Weighted Average Remaining Contractual Term (in years)	8 years 8 months 12 days
Options outstanding at end of period, Aggregate Intrinsic Value (in thousands)	$ 10,210
Options exercisable at end of period, Aggregate Intrinsic Value (in thousands)	4,645
Expected to vest after end of period, Aggregate Intrinsic Value (in thousands)	$ 5,565