Stock-Based Compensation and Stock Repurchases (Schedule Of Stock Options Outstanding And Exercisable) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Equity And Stock-Based Compensation [Line Items]
Weighted Average Exercise Price of Options Outstanding, Granted	$ 11.87	$ 13.30	$ 8.56
Weighted average remaining years of contractual life	2 years 7 months 10 days	2 years 10 months 21 days	2 years 4 months 24 days	4 years 8 months 12 days
Aggregate Intrinsic Value, Beginning balance	$ 2,188,011	$ 4,197,000	$ 938,503
Aggregate Intrinsic Value, Exercised	220,002	327,170	374,022
Aggregate Intrinsic Value, Ending balance	$ 3,615,191	$ 2,188,011	$ 4,197,000	$ 938,503
Class A [Member]
Equity And Stock-Based Compensation [Line Items]
Common Stock Options Outstanding, Beginning balance	486,565	568,250	709,850
Common Stock Options Outstanding, Granted	169,327	112,000	80,000
Common Stock Options Outstanding, Exercised	(46,815)	(185,685)	(157,600)
Common Stock Options Outstanding, Expired	(74,000)	(8,000)	(64,000)
Common Stock Options Outstanding, Ending balance	535,077	486,565	568,250	709,850
Weighted Average Exercise Price of Options Outstanding, Beginning price	$ 8.68	$ 6.88	$ 6.66
Weighted Average Exercise Price of Options Outstanding, Granted	11.87	13.30	8.56
Weighted Average Exercise Price of Options Outstanding, Exercised	9.50	6.09	6.21
Weighted Average Exercise Price of Options Outstanding, Expired	7.02	6.23	6.83
Weighted Average Exercise Price of Options Outstanding, Ending price	$ 9.84	$ 8.68	$ 6.88	$ 6.66
Class B [Member]
Equity And Stock-Based Compensation [Line Items]
Common Stock Options Outstanding, Beginning balance		185,100	185,100
Common Stock Options Outstanding, Granted
Common Stock Options Outstanding, Exercised		(185,100)
Common Stock Options Outstanding, Ending balance			185,100	185,100
Weighted Average Exercise Price of Options Outstanding, Beginning price		$ 9.90	$ 9.90
Weighted Average Exercise Price of Options Outstanding, Exercised		$ 9.90
Weighted Average Exercise Price of Options Outstanding, Ending price			$ 9.90	$ 9.90