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Stockholders' Equity - Narrative (Details) - USD ($) |  |  |  |  |  |  | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Nov. 05, 2021 | Oct. 15, 2021 | Nov. 10, 2020 | Oct. 11, 2019 | Oct. 25, 2018 | Sep. 07, 2018 | Dec. 31, 2021 | Dec. 31, 2020 | Sep. 30, 2020 | Sep. 30, 2021 | Feb. 27, 2015
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Stock compensation expense |  |  |  |  |  |  | $ 179,000 | $ 222,000 |  |  |
Restricted Stock |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Stock compensation expense |  |  |  |  |  |  | 136,000 | 25,000 |  |  |
Unrecognized expense |  |  |  |  |  |  | 72,000 |  |  | $ 144,000 |
Weighted average fair value (in dollars per share) | $ 37.13 | $ 34.41 | $ 31.20 |  |  |  |  |  |  |  |
Options |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Stock compensation expense |  |  |  |  |  |  | 60,000 | $ 60,000 |  |  |
Unrecognized expense |  |  |  |  |  |  | $ 73,000 |  |  | $ 134,000 |
Unrecognized compensation cost, expected recognition period |  |  |  |  |  |  |  | 1 year |  |  |
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 | 2,224 | 2,500 | 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 |  |  |  |  |  |
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 | 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 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 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 |  |  |
2020 Option Grants | Options |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |
Grants in period, weighted average (in dollars per share) |  |  |  |  |  |  | $ 3.20 |  |  |  |

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