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Stockholders' Equity - Narrative (Details) - USD ($) |  |  |  |  |  |  |  | 3 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Nov. 10, 2020 | Oct. 11, 2019 | Feb. 11, 2019 | Oct. 25, 2018 | Sep. 07, 2018 | Sep. 05, 2018 | Dec. 31, 2016 | Dec. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2020 | Dec. 30, 2020 | Oct. 10, 2019 | Feb. 27, 2015
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares authorized to be repurchased (up to) |  |  |  |  |  |  |  |  |  |  |  | 7,000 |
Stock compensation expense |  |  |  |  |  |  |  | $ 222,000 | $ 193,000 |  |  |  |
Restricted Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Stock compensation expense |  |  |  |  |  |  |  | 25,000 | 26,000 |  |  |  |
Unrecognized expense |  |  |  |  |  |  |  | 159,000 |  | $ 0 |  |  |
Weighted average fair value (in dollars per share) | $ 31.20 |  |  |  |  |  |  |  |  |  |  |  |
Options |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Stock compensation expense |  |  |  |  |  |  |  | $ 60,000 | $ 82,000 |  |  |  |
Unrecognized expense |  |  |  |  |  |  |  |  |  | $ 376,000 | $ 316,000 |  |
Unrecognized compensation cost, expected recognition period |  |  |  |  |  |  |  | 1 year 5 months 19 days |  |  |  |  |
2015 Option Grants |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares authorized to be repurchased (up to) |  |  |  |  |  |  |  |  |  |  |  |  | 1,250,000
2015 Option Grants | Restricted Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Number of restricted shares awarded | 5,885 |  |  |  |  |  |  |  |  |  |  |  |
2015 Option Grants | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Award vesting period |  |  |  |  |  |  |  | 1 year |  |  |  |  |
2015 Option Grants | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Award vesting period |  |  |  |  |  |  |  | 6 years |  |  |  |  |
2020 Option Grants |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Granted (in shares) |  | 118,000 |  |  |  |  |  |  |  |  |  |  |
Shares issued (in dollars per share) |  | $ 33.96 |  |  |  |  |  |  |  |  |  |  |
Percentage of options |  |  |  |  |  |  |  |  |  | 25.00% |  |  |
Period following an executive's termination of employment for a number of reasons |  | 18 months |  |  |  |  |  |  |  |  |  |  |
Period following an executive's termination of employment without cause |  | 12 months |  |  |  |  |  |  |  |  |  |  |
2020 Option Grants | Tranche One |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of options |  | 25.00% |  |  |  |  |  |  |  |  |  |  |
Period of consecutive trading days |  | 20 days |  |  |  |  |  |  |  |  |  |  |
Amount per share (in dollars per share) |  | $ 35.00 |  |  |  |  |  |  |  |  |  |  |
2020 Option Grants | Tranche Two |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of options |  | 25.00% |  |  |  |  |  |  |  |  |  |  |
Period of consecutive trading days |  | 20 days |  |  |  |  |  |  |  |  |  |  |
Amount per share (in dollars per share) |  | $ 40.00 |  |  |  |  |  |  |  |  |  |  |
2020 Option Grants | Tranche Three |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of options |  | 25.00% |  |  |  |  |  |  |  |  |  |  |
Period of consecutive trading days |  | 20 days |  |  |  |  |  |  |  |  |  |  |
Amount per share (in dollars per share) |  | $ 45.00 |  |  |  |  |  |  |  |  |  |  |
2020 Option Grants | Tranche Four |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of options |  | 25.00% |  |  |  |  |  |  |  |  |  |  |
Period of consecutive trading days |  | 20 days |  |  |  |  |  |  |  |  |  |  |
Amount per share (in dollars per share) |  | $ 50.00 |  |  |  |  |  |  |  |  |  |  |
2020 Option Grants | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  |  |  |  |  |  |  |  | $ 35.00 |  |  |
2020 Option Grants | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  |  |  |  |  |  | $ 40.00 |  |  |  |  |
2019 Option Grants |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Shares issued (in dollars per share) |  |  |  | $ 33.34 |  |  |  |  |  |  |  |  |
Period following an executive's termination of employment for a number of reasons |  |  |  | 18 months |  |  |  |  |  |  |  |  |
Period following an executive's termination of employment without cause |  |  |  | 12 months |  |  |  |  |  |  |  |  |
Number of awards vesting (in shares) |  |  |  |  |  |  |  | 0 |  |  |  |  |
2019 Option Grants | Chief Financial Officer |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Granted (in shares) |  |  |  | 10,000 |  |  |  |  |  |  |  |  |
2019 Option Grants | Tranche One |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Period of consecutive trading days |  |  |  | 20 days |  |  |  |  |  |  |  |  |
Amount per share (in dollars per share) |  |  |  | $ 40.00 |  |  |  |  |  |  |  |  |
Number of awards vesting (in shares) |  |  |  | 3,333 |  |  |  |  |  |  |  |  |
2019 Option Grants | Tranche Two |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Period of consecutive trading days |  |  |  | 20 days |  |  |  |  |  |  |  |  |
Amount per share (in dollars per share) |  |  |  | $ 45.00 |  |  |  |  |  |  |  |  |
Number of awards vesting (in shares) |  |  |  | 3,333 |  |  |  |  |  |  |  |  |
2019 Option Grants | Tranche Three |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Period of consecutive trading days |  |  |  | 20 days |  |  |  |  |  |  |  |  |
Amount per share (in dollars per share) |  |  |  | $ 50.00 |  |  |  |  |  |  |  |  |
Number of awards vesting (in shares) |  |  |  | 3,334 |  |  |  |  |  |  |  |  |
2019 Option Grants | Options |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Grants in period, weighted average (in dollars per share) |  |  |  |  |  |  |  | $ 7.10 |  |  |  |  |
2019 Option Grants | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  |  |  |  |  |  | $ 40.00 |  |  |  |  |
2018 Option Grants |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Shares issued (in dollars per share) |  |  |  |  | $ 33.60 |  |  |  |  |  |  |  |
Percentage of options |  |  |  |  |  |  |  | 0.00% |  | 25.00% |  |  |
Period following an executive's termination of employment for a number of reasons |  |  |  |  | 18 months |  |  |  |  |  |  |  |
Period following an executive's termination of employment without cause |  |  |  |  | 12 months |  |  |  |  |  |  |  |
2018 Option Grants | Chief Financial Officer |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Granted (in shares) |  |  |  |  | 90,000 |  |  |  |  |  |  |  |
2018 Option Grants | Chief Executive Officer |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Granted (in shares) |  |  |  |  | 210,000 |  |  |  |  |  |  |  |
2018 Option Grants | Tranche One |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of options |  |  |  |  | 25.00% |  |  |  |  |  |  |  |
Period of consecutive trading days |  |  |  |  | 20 days |  |  |  |  |  |  |  |
Amount per share (in dollars per share) |  |  |  |  | $ 35.00 |  |  |  |  |  |  |  |
2018 Option Grants | Tranche One | Chief Executive Officer |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Period of consecutive trading days |  |  | 20 days |  |  |  |  |  |  |  |  |  |
Amount per share (in dollars per share) |  |  | $ 35.00 |  |  |  |  |  |  |  |  |  |
Number of shares expected to vest (in shares) |  |  | 26,250 |  |  |  |  |  |  |  |  |  |
2018 Option Grants | Tranche Two |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of options |  |  |  |  | 25.00% |  |  |  |  |  |  |  |
Period of consecutive trading days |  |  |  |  | 20 days |  |  |  |  |  |  |  |
Amount per share (in dollars per share) |  |  |  |  | $ 40.00 |  |  |  |  |  |  |  |
2018 Option Grants | Tranche Two | Chief Executive Officer |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Period of consecutive trading days |  |  | 20 days |  |  |  |  |  |  |  |  |  |
Amount per share (in dollars per share) |  |  | $ 40.00 |  |  |  |  |  |  |  |  |  |
Number of shares expected to vest (in shares) |  |  | 26,250 |  |  |  |  |  |  |  |  |  |
2018 Option Grants | Tranche Three |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of options |  |  |  |  | 25.00% |  |  |  |  |  |  |  |
Period of consecutive trading days |  |  |  |  | 20 days |  |  |  |  |  |  |  |
Amount per share (in dollars per share) |  |  |  |  | $ 45.00 |  |  |  |  |  |  |  |
2018 Option Grants | Tranche Four |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of options |  |  |  |  | 25.00% |  |  |  |  |  |  |  |
Period of consecutive trading days |  |  |  |  | 20 days |  |  |  |  |  |  |  |
Amount per share (in dollars per share) |  |  |  |  | $ 50.00 |  |  |  |  |  |  |  |
2018 Option Grants | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  |  |  |  |  |  |  |  | $ 35.00 |  |  |
2018 Option Grants | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  |  |  |  |  |  | $ 40.00 |  |  |  |  |
2016 Option Grants |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Shares issued (in dollars per share) |  |  |  |  |  |  | $ 27.15 |  |  |  |  |  |
Period following an executive's termination of employment for a number of reasons |  |  |  |  |  |  | 18 months |  |  |  |  |  |
Number of awards vesting (in shares) |  |  |  |  |  |  |  | 0 |  |  |  |  |
2016 Option Grants | Chief Executive Officer |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Granted (in shares) |  |  |  |  |  |  | 300,000 |  |  |  |  |  |
2016 Option Grants | Board of Directors Chairman |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Granted (in shares) |  |  |  |  |  |  | 225,000 |  |  |  |  |  |
Shares forfeited (in shares) |  |  |  |  |  | 187,500 |  |  |  |  |  |  |
2016 Option Grants | Tranche One |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of options |  |  |  |  |  |  | 25.00% |  |  |  |  |  |
Period of consecutive trading days |  |  |  |  |  |  | 20 days |  |  |  |  |  |
Amount per share (in dollars per share) |  |  |  |  |  |  | $ 60.00 |  |  |  |  |  |
2016 Option Grants | Tranche Two |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of options |  |  |  |  |  |  | 25.00% |  |  |  |  |  |
Period of consecutive trading days |  |  |  |  |  |  | 20 days |  |  |  |  |  |
Amount per share (in dollars per share) |  |  |  |  |  |  | $ 75.00 |  |  |  |  |  |
2016 Option Grants | Tranche Three |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of options |  |  |  |  |  |  | 25.00% |  |  |  |  |  |
Period of consecutive trading days |  |  |  |  |  |  | 20 days |  |  |  |  |  |
Amount per share (in dollars per share) |  |  |  |  |  |  | $ 90.00 |  |  |  |  |  |
2016 Option Grants | Tranche Four |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of options |  |  |  |  |  |  | 25.00% |  |  |  |  |  |
Period of consecutive trading days |  |  |  |  |  |  | 20 days |  |  |  |  |  |
Amount per share (in dollars per share) |  |  |  |  |  |  | $ 105.00 |  |  |  |  |  |
2016 Option Grants | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  |  |  |  |  |  | $ 60.00 |  |  |  |  |
2019 Modified Option Grants | Tranche One | Chief Executive Officer |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares expected to vest (in shares) |  |  | 26,250 |  |  |  |  |  |  |  |  |  |
2019 Modified Option Grants | Tranche Two | Chief Executive Officer |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares expected to vest (in shares) |  |  | 26,250 |  |  |  |  |  |  |  |  |  |
2019 Modified Option Grants | Options |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Grants in period, weighted average (in dollars per share) |  |  |  |  |  |  |  | 1.40 |  |  |  |  |
2019 Modified Option Grants | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  | $ 40.00 |  |  |  |  | 35.00 |  |  |  |  |
2020 Option Grants | Options |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Grants in period, weighted average (in dollars per share) |  |  |  |  |  |  |  | $ 3.20 |  |  |  |  |

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