Share-Based Compensation And Share Repurchase Plans (Narrative) (Details) - USD ($)		3 Months Ended	12 Months Ended
	Nov. 07, 2017	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 10, 2020	Mar. 14, 2019	Sep. 30, 2017
Equity And Stock-Based Compensation [Line Items]
Unrecognized estimated compensation cost related to non-vested stock options granted			$ 1,100,000
Recognition period of unrecognized compensation cost			1 year 10 months 2 days
Stock Option [Member]
Equity And Stock-Based Compensation [Line Items]
Compensation expense			$ 458,000	$ 425,000	$ 310,000
Proceeds from stock option exercises			906,000	361,000	$ 574,000
Restricted Stock Units (RSUs) [Member]
Equity And Stock-Based Compensation [Line Items]
Compensation expense			1,000,000	$ 1,000,000
Unrecognized estimated compensation cost related to non-vested stock options granted			$ 1,300,000
Shares granted			59,258	97,600
Forfeiture of shares			25,000	6,410
2017 Stock Repurchase Plan [Member]
Equity And Stock-Based Compensation [Line Items]
Stock buy-back program period			2 years
$25 Million Stock Repurchase Program [Member]
Equity And Stock-Based Compensation [Line Items]
Repurchase program, amount authorized							$ 25,000,000
Class A [Member]
Equity And Stock-Based Compensation [Line Items]
Shares granted			219,408	126,840	169,762
2010 Stock Incentive Plan [Member]
Equity And Stock-Based Compensation [Line Items]
Additional shares authorized	947,460
Common Stock shares remaining for future issuances								302,540
Repurchase program, shares authorized								302,540
2010 Stock Incentive Plan [Member] | Class A Nonvoting Common Stock [Member]
Equity And Stock-Based Compensation [Line Items]
Common Stock authorized for issuance under 2010 Stock Incentive Plan			1,250,000
Common Stock shares remaining for future issuances			778,304
2010 Stock Incentive Plan [Member] | Class A [Member]
Equity And Stock-Based Compensation [Line Items]
Shares granted		0
2010 Stock Incentive Plan [Member] | Minimum [Member]
Equity And Stock-Based Compensation [Line Items]
Vesting period of stock options and RSU			0 years
2010 Stock Incentive Plan [Member] | Maximum [Member]
Equity And Stock-Based Compensation [Line Items]
Vesting period of stock options and RSU			4 years
Subsequent Event [Member] | 2017 Stock Repurchase Plan [Member]
Equity And Stock-Based Compensation [Line Items]
Repurchase program, amount authorized						$ 25,000,000
Subsequent Event [Member] | Class A [Member] | 2017 Stock Repurchase Plan [Member]
Equity And Stock-Based Compensation [Line Items]
Repurchase program, remaining amount authorized						$ 26,000,000