Stock-Based Compensation (Narrative) (Details)			12 Months Ended
	May 11, 2017 USD ($) $ / shares shares	May 20, 2016 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) qtr plan $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 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			568,525	547,625
Shares granted, shares | shares			32,200
Weighted average grant date fair value, granted (in usd per share) | $ / shares			$ 16.77
Weighted average fair value on grant date | $ / shares			7.36	$ 9.88	$ 2.73
Weighted-Average Exercise Price Per Share, Granted (in usd per share) | $ / shares			$ 15.40
Proceeds from exercise of stock options			$ 378,000	$ 474,000	$ 458,000
Equity based compensation expense			895,000	863,000	511,000
Unrecognized compensation cost related to non-vested equity based compensation			$ 2,000,000.0
Unrecognized equity based compensation weighted average period (in years)			1 year 6 months 21 days
Tax benefit from the exercise of stock options and vesting of share based payments			$ 310,000	428,000	0
Excess tax benefit from the exercise of stock options			227,000
Accounting Standards Update 2016-09 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Tax benefit from the exercise of stock options and vesting of share based payments			421,000
Excess tax benefit from the exercise of stock options			$ 227,000
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 4 months 24 days
Aggregate intrinsic value for all options outstanding			$ 3,200,000
Weighted average remaining contractual term for exercisable options (in years)			3 years 9 months 18 days
Aggregate intrinsic value of stock options exercised			$ 782,000	720,000	182,000
Aggregate intrinsic value of exercisable options			2,100,000
Proceeds from exercise of stock options			378,000	474,000	458,000
Fair value of shares vested			443,000	495,000	$ 264,000
Stock Options And Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity based compensation expense			$ 667,000	$ 648,000
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			40,872
Shares granted, shares | shares			18,404	36,481	35,845
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%
Equity based compensation expense			$ 121,000	$ 79,000
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			32,200	10,700	18,250
Weighted average grant date fair value, granted (in usd per share) | $ / shares			$ 16.77	$ 26.40	$ 7.18
Aggregate intrinsic value for all options outstanding			$ 813,000
Fair value of shares vested			$ 453,000	$ 394,000	$ 129,000
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			327,839
Common stock reserved for issuance pursuant to outstanding awards | shares			602,737
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			68,000
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
Options granted to non-employee directors upon re-election | shares		16,000
Stock granted, value	$ 167,000	$ 136,000
Weighted average grant date fair value, granted (in usd per share) | $ / shares	$ 20.90	$ 16.97
Options granted in period, fair value		$ 139,000
Weighted average fair value on grant date | $ / shares		$ 8.71
Share issuances for compensation purposes, shares | shares	8,000	8,000
Stock Grant Plan For Non-Employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted for non-employee directors upon re-election, shares | shares			1,000
Share issuances for compensation purposes, shares | shares			8,000		4,000
Equity based compensation expense			$ 107,000	$ 136,000	$ 41,000
Weighted average grant date fair value (in usd per share) | $ / shares					$ 10.36