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Stock Options (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	May 07, 2015	May 07, 2009
Qualified Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value of options granted (in dollars per share)	$ 39.85	$ 38.77	$ 36.00
Stock option expense	$ 451	$ 482	$ 597
Total unrecognized compensation cost related to non-vested share-based compensation arrangements	$ 755
Period cost is expected to be recognized (years)	5 years
Granted (in shares)	12,150	9,500	10,750
Exercise of stock options (in shares)	28,100	41,205	54,945
Non Qualified Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option expense	$ 8	$ 22	$ 22
Total unrecognized compensation cost related to non-vested share-based compensation arrangements	$ 0
Period cost is expected to be recognized (years)	5 years
Granted (in shares)	0	0	0
Exercise of stock options (in shares)	34,900	26,800	45,400
Proceeds from stock options exercised	$ 1,480	$ 1,115	$ 1,032
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option expense	2,810	$ 1,946	$ 1,250
Total unrecognized compensation cost related to non-vested share-based compensation arrangements	$ 5,775
Period cost is expected to be recognized (years)	4 years
Weighted average remaining contractual life (years)	2 years 5 months 23 days	2 years 6 months 10 days	2 years 8 months 8 days
Restricted Stock Units (RSUs) \| Year One after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	25.00%
Award vesting period (years)	1 year
Restricted Stock Units (RSUs) \| Year Two after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	25.00%
Restricted Stock Units (RSUs) \| Year Three after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	25.00%
Restricted Stock Units (RSUs) \| Year Four after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	25.00%
2015 ISO Plan \| Qualified Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for options to be issued (in shares)				400,000
2015 ISO Plan \| Qualified Stock Options \| Year One after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (years)	1 year
2015 ISO Plan \| Qualified Stock Options \| Year One after Grant Date \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%
2015 ISO Plan \| Qualified Stock Options \| Year Two after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%
2015 ISO Plan \| Qualified Stock Options \| Year Three after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%
2015 ISO Plan \| Qualified Stock Options \| Year Four after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%
2015 ISO Plan \| Qualified Stock Options \| Year Five after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%
2009 Equity Incentive Plan \| Non Qualified Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for options to be issued (in shares)					500,000
2009 Equity Incentive Plan \| Non Qualified Options \| Year One after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (years)	1 year
2009 Equity Incentive Plan \| Non Qualified Options \| Year One after Grant Date \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%
2009 Equity Incentive Plan \| Non Qualified Options \| Year Two after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%
2009 Equity Incentive Plan \| Non Qualified Options \| Year Three after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%
2009 Equity Incentive Plan \| Non Qualified Options \| Year Four after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%
2009 Equity Incentive Plan \| Non Qualified Options \| Year Five after Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award	20.00%