Share-Based Compensation (Narrative) (Details)			12 Months Ended
	May 10, 2018 USD ($) $ / shares shares	May 11, 2017 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) qtr plan $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock-based compensation plans | plan			3
Common stock reserved for issuance pursuant to outstanding awards | shares			523,042	568,525
Shares granted, shares | shares			32,350
Weighted average grant date fair value, granted (in usd per share) | $ / shares			$ 18.67
Proceeds from exercise of stock options			$ 525,000	$ 378,000
Equity based compensation expense			936,000	895,000
Unrecognized compensation cost related to non-vested equity based compensation			$ 2,200,000
Unrecognized equity based compensation weighted average period (in years)			2 years 11 months 15 days
Tax benefit from the exercise of stock options and vesting of share based payments			$ 329,000	310,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)			4 years
Expiration of stock options from date of grant (in years)			7 years
Weighted average remaining contractual term (in years)			4 years
Aggregate intrinsic value for all options outstanding			$ 3,600,000
Weighted average remaining contractual term for exercisable options (in years)			3 years 2 months 19 days
Aggregate intrinsic value of exercisable options			$ 3,100,000
Aggregate intrinsic value of stock options exercised			1,000,000.0	782,000
Proceeds from exercise of stock options			525,000	378,000
Fair value of shares vested			616,000	443,000
Tax benefit from the exercise of stock options and vesting of share based payments			303,000	421,000
Excess tax benefit from the exercise of stock options			155,000	227,000
Stock Options And Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity based compensation expense			$ 675,000	$ 667,000
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for future issuance, shares | shares			174,469
Number of additional shares authorized for issuance | shares			150,000
Maximum contribution per plan year			$ 6,500
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%
Shares granted, shares | shares			16,403	18,404
Equity based compensation expense			$ 117,000	$ 121,000
Employee Stock Purchase Plan [Member] | Minimum [Member]
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 [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payroll deduction for employee stock purchase plan percentage			10.00%
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)			4 years
Restricted stock units to common stock ratio, shares entitled, shares | shares			1
Restricted Shares and Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted, shares | shares			32,350	32,200
Weighted average grant date fair value, granted (in usd per share) | $ / shares			$ 18.67	$ 16.77
Aggregate intrinsic value for all options outstanding			$ 995,000
Fair value of shares vested			$ 553,000	$ 453,000
Stock Incentive Plan [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for future issuance, shares | shares			259,789
Common stock reserved for issuance pursuant to outstanding awards | shares			559,453
Non Employee Director Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for future issuance, shares | shares			60,000
Common stock reserved for issuance pursuant to outstanding awards | shares			16,000
Number of shares granted for non-employee directors upon re-election, shares | shares			2,000
Number of quarterly installments in which awards will vest | qtr			4
Stock issued during period, shares | shares	8,000	8,000
Stock granted, value	$ 130,000	$ 167,000
Weighted average grant date fair value, granted (in usd per share) | $ / shares	$ 16.25	$ 20.90
Number of shares vested | shares			4,000
Aggregate intrinsic value for all options outstanding			$ 71,000
Non Employee Director Stock Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted, shares | shares		2,000
Stock Grant Plan For Non-Employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock issued during period, shares | shares			8,000	8,000
Equity based compensation expense			$ 144,000	$ 107,000