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Common Stock and Options - Narrative (Details) - USD ($) |  |  |  |  |  |  | 1 Months Ended | 12 Months Ended |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Nov. 10, 2020 | Oct. 11, 2019 | Feb. 11, 2019 | Oct. 25, 2018 | Sep. 07, 2018 | Dec. 31, 2016 | Nov. 30, 2017 | Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2019 | Oct. 15, 2019 | Oct. 10, 2019 | Oct. 03, 2018 | May 31, 2017 | Mar. 31, 2017 | Feb. 27, 2015
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares authorized to be repurchased (up to) |  |  |  |  |  |  |  |  |  |  | 7,000 | 7,000 |  | 2,000,000 | 5,000,000 |
Total stock-based compensation expense |  |  |  |  |  |  |  | $ 1,230,000 | $ 1,306,000 | $ 824,000 |  |  |  |  |  |
Employee stock options granted (in shares) |  |  |  |  |  |  |  | 0 | 118,000 | 10,000 |  |  |  |  |  |
Shares issued (in dollars per share) |  |  |  |  |  |  |  |  |  |  |  |  | $ 34.00 |  |  |
Period of consecutive trading days |  |  | 20 days |  |  |  |  |  |  |  |  |  |  |  |  |
Common shares available |  |  |  |  |  |  |  | 218,000 | 293,000 | 227,500 |  |  |  |  |  |
Restricted Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Award vesting period |  |  |  |  |  |  | 2 years 6 months |  |  |  |  |  |  |  |  |
Total stock-based compensation expense |  |  |  |  |  |  |  | $ 144,000 | $ 69,000 | $ 104,000 |  |  |  |  |  |
Number of restricted shares awarded | 5,885 |  |  |  |  |  | 5,000 | 5,885 |  |  |  |  |  |  |  |
Weighted average fair value (in dollars per share) | $ 31.20 |  |  |  |  |  | $ 31.95 | $ 31.20 |  |  |  |  |  |  |  |
Number of restricted shares vested |  |  |  |  |  |  |  | 0 | 5,666 | 1,667 |  |  |  |  |  |
Unrecognized expense |  |  |  |  |  |  |  | $ 40,000 | $ 0 |  |  |  |  |  |  |
Aggregate value of shares vested |  |  |  |  |  |  |  |  | 251,000 | $ 53,000 |  |  |  |  |  |
Options |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total stock-based compensation expense |  |  |  |  |  |  |  | 242,000 | 504,000 | 674,000 |  |  |  |  |  |
Unrecognized expense |  |  |  |  |  |  |  | 134,000 | $ 376,000 |  |  |  |  |  |  |
Unrecognized compensation cost, expected recognition period |  |  |  |  |  |  |  |  | 8 months 19 days |  |  |  |  |  |  |
Board of Directors Fees |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total stock-based compensation expense |  |  |  |  |  |  |  | $ 844,000,000 | $ 733,000,000 | $ 869,000,000 |  |  |  |  |  |
Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  | $ 35.00 |  |  |  |  |  |  |  |  |  |  |  |  |
2015 Option Grants |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares authorized to be repurchased (up to) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,250,000
2015 Option Grants | Options |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common shares available |  |  |  |  |  |  |  | 1,014,500 |  |  |  |  |  |  |  |
2015 Option Grants | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Award vesting period |  |  |  |  |  |  |  | 1 year |  |  |  |  |  |  |  |
2015 Option Grants | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Award vesting period |  |  |  |  |  |  |  | 6 years |  |  |  |  |  |  |  |
2020 Option Grants |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Employee stock options 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 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of awards vesting (in shares) |  |  |  |  |  |  |  | 0 |  |  |  |  |  |  |  |
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 | Options |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Grants in period, weighted average (in dollars per share) |  |  |  |  |  |  |  | $ 3.20 |  |  |  |  |  |  |  |
2020 Option Grants | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  |  |  |  |  |  | $ 40.00 | $ 35.00 |  |  |  |  |  |  |
2020 Option Grants | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  |  |  |  |  |  |  | $ 35.00 |  |  |  |  |  |  |
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 | 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 | Chief Financial Officer |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Employee stock options granted (in shares) |  |  |  | 10,000 |  |  |  |  |  |  |  |  |  |  |  |
2019 Option Grants | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  |  | 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 |  |  |  |  |  |  |  |  |  |  |
Number of awards vesting (in shares) |  |  |  |  |  |  |  | 0 |  |  |  |  |  |  |  |
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 | Chief Financial Officer |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Employee stock options granted (in shares) |  |  |  |  | 90,000 |  |  |  |  |  |  |  |  |  |  |
2018 Option Grants | Chief Executive Officer |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Employee stock options granted (in shares) |  |  |  |  | 210,000 |  |  |  |  |  |  |  |  |  |  |
2018 Option Grants | Chief Executive Officer | Tranche One |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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 | Chief Executive Officer | Tranche Two |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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 | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  |  |  |  |  |  |  | $ 35.00 |  |  |  |  |  |  |
2018 Option Grants | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
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 | 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 | Chief Executive Officer |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Employee stock options granted (in shares) |  |  |  |  |  | 300,000 |  |  |  |  |  |  |  |  |  |
2016 Option Grants | Board of Directors Chairman |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Employee stock options granted (in shares) |  |  |  |  |  | 225,000 |  |  |  |  |  |  |  |  |  |
2016 Option Grants | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  |  |  |  |  |  | $ 60.00 |  |  |  |  |  |  |  |
2019 Option Grants | Options |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Grants in period, weighted average (in dollars per share) |  |  |  |  |  |  |  | $ 1.40 |  |  |  |  |  |  |  |
2019 Option Grants | Chief Executive Officer | Tranche One |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares forfeited (in shares) |  |  | 26,250 |  |  |  |  |  |  |  |  |  |  |  |  |
2019 Option Grants | Chief Executive Officer | Tranche Two |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of consecutive trading days |  |  | 20 days |  |  |  |  |  |  |  |  |  |  |  |  |
Shares forfeited (in shares) |  |  | 26,250 |  |  |  |  |  |  |  |  |  |  |  |  |
2019 Option Grants | Maximum [Member] | Chief Executive Officer | Tranche Two |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class Of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  | $ 40.00 |  |  |  |  |  |  |  |  |  |  |  |  |

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