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Stock Options - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	May 02, 2019	May 07, 2015	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option term (years)			10 years
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)			$ 38.33	$ 39.85	$ 38.77
Granted (in shares)			13,950	12,150	9,500
Stock option expense			$ 500	$ 500	$ 500
Total unrecognized compensation cost related to non-vested share-based compensation arrangements			$ 800
Period cost is expected to be recognized (years)			5 years
Exercise of stock options (in shares)			31,300	28,100	41,205
Non Qualified Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)			0	0	0
Stock option expense			$ 0	$ 10	$ 20
Total unrecognized compensation cost related to non-vested share-based compensation arrangements			$ 0
Exercise of stock options (in shares)			2,300	34,900	26,800
Proceeds from stock options exercised			$ 100	$ 1,500	$ 1,100
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option expense			3,700	$ 2,800	$ 1,900
Total unrecognized compensation cost related to non-vested share-based compensation arrangements			$ 6,200
Period cost is expected to be recognized (years)			4 years
Weighted average remaining contractual life (years)			1 year 11 months 12 days	2 years 5 months 23 days	2 years 6 months 10 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%	25.00%
Award vesting period (years)			3 years	1 year	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%	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%	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%	25.00%
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award			50.00%
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage of award			50.00%
Option term (years)			3 years
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%