Share-Based Compensation (Narrative) (Details)		3 Months Ended		9 Months Ended
	May 13, 2021 USD ($) $ / shares shares	Sep. 30, 2021 USD ($) qtr stock-based_complensation_plan shares	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) qtr stock-based_complensation_plan $ / shares shares	Sep. 30, 2020 USD ($) shares	Dec. 31, 2020 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock-based compensation plans | stock-based_complensation_plan		3		3
Common stock reserved for issuance pursuant to outstanding awards		340,200		340,200		419,100
Weighted average grant date fair value (in dollars per share) | $ / shares				$ 27.96
Number of shares vested				6,000
Aggregate fair value of outstanding restricted shares and restricted stock units | $		$ 2,500,000		$ 2,500,000
Aggregate fair value of restricted shares and restricted stock units | $				199,000	$ 179,000
Proceeds from exercise of stock options | $				$ 292,000	$ 322,000
Number of shares vested				0	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants, Forfeitures and Expirations in Period				0
Shares, Granted (in shares)				8,000
Unvested shares		69,604		69,604		68,454
Equity based compensation expense | $		$ 327,000	$ 305,000	$ 999,000	$ 863,000
Unrecognized compensation cost related to non-vested equity based compensation | $		$ 2,000,000.0		$ 2,000,000.0
Unrecognized equity based compensation weighted average period, years				2 years 3 months 14 days
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for future issuance (in shares)		127,126		127,126
Common stock reserved for issuance pursuant to outstanding awards		395,804		395,804
Vesting period, years				4 years
Expiration of stock options from date of grant				7 years
Weighted average remaining contractual term, years				3 years 3 months 29 days
Aggregate intrinsic value for all options outstanding | $		$ 6,600,000		$ 6,600,000
Weighted average remaining contractual term for exercisable options, years				2 years 4 months 9 days
Aggregate intrinsic value of exercisable options | $		4,800,000		$ 4,800,000
Aggregate intrinsic value of stock options exercised | $				2,300,000	2,100,000
Proceeds from exercise of stock options | $				292,000	322,000
Equity based compensation expense | $		118,000	115,000	$ 366,000	343,000
Restricted Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Granted (in shares)				8,000
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, years				4 years
Restricted stock units to common stock ratio, shares entitled, shares				1
Shares, Granted (in shares)				0
Equity based compensation expense | $		$ 120,000	102,000	$ 368,000	304,000
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for future issuance (in shares)		129,411		129,411
Maximum contribution per plan year | $				$ 6,500
Number of shares purchased under the plan		7,380		7,380
Equity based compensation expense | $		$ 33,000	31,000	$ 96,000	79,000
Employees can purchase stock at the percentage rate of the lower of the market price on the first or last day of the offering period (as a percent)				85.00%
Employee Stock Purchase Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payroll deduction for employee stock purchase plan percentage				1.00%
Employee Stock Purchase Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payroll deduction for employee stock purchase plan percentage				10.00%
Non Employee Director Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for future issuance (in shares)		36,000		36,000
Common stock reserved for issuance pursuant to outstanding awards		8,000		8,000
Number of shares granted for non-employee directors upon re-election, shares				2,000
Number of quarterly installments in which awards will vest | qtr		4		4
Stock issued during period, shares	8,000
Stock granted, value | $	$ 224,000
Weighted average grant date fair value (in dollars per share) | $ / shares	$ 27.96
Number of shares vested				2,000
Unvested shares		6,000		6,000
Aggregate fair value of the unvested shares based on the closing price of entity's common stock | $		$ 213,000		$ 213,000
Equity based compensation expense | $		$ 56,000	$ 57,000	$ 169,000	$ 137,000