Stock-Based Compensation And Stock Repurchases (Schedule Of Stock Options Outstanding And Exercisable) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity And Stock-Based Compensation [Line Items]
Number of Stock Options, Granted	219,408
Weighted Average Exercise Price of Options Outstanding, Granted	$ 16.12
Class A [Member]
Equity And Stock-Based Compensation [Line Items]
Number of Stock Options, Beginning balance	586,469	524,589
Number of Stock Options, Granted	219,408	126,840
Number of Stock Options, Exercised	(67,500)	(60,000)
Number of Stock Options, Forfeited	(25,000)	(4,960)
Number of Stock Options Outstanding, Ending balance	713,377	586,469	524,589
Weighted Average Exercise Price of Options Outstanding, Beginning price	$ 14.01	$ 12.50
Weighted Average Exercise Price of Options Outstanding, Granted	16.12	16.40
Weighted Average Exercise Price of Options Outstanding, Exercised	13.42	6.02
Weighted Average Exercise Price of Options Outstanding, Forfeited	13.42	12.08
Weighted Average Exercise Price of Options Outstanding, Ending price	$ 14.74	$ 14.01	$ 12.50
Weighted Average Remaining Years of Contractual Life	3 years 6 months 11 days	2 years 10 months 17 days	3 years 1 month 24 days
Aggregate Intrinsic Value, Beginning balance	$ 1,530,528	$ 3,054,325
Aggregate Intrinsic Value, Exercised	185,175	610,249
Aggregate Intrinsic Value, Ending balance	$ 1,993,628	$ 1,530,528	$ 3,054,325