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Common Stock and Options - Narrative (Details) - USD ($) |  |  | 1 Months Ended | 3 Months Ended | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Sep. 07, 2018 | Dec. 31, 2016 | Nov. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2016 | May 31, 2017 | Mar. 31, 2017 | Jan. 27, 2017 | Sep. 30, 2015 | Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of shares authorized to be repurchased (up to) (in shares) |  |  |  |  |  | 7,000,000 |  | 2,000,000 | 5,000,000 |  | 170,000 | 105,000
Total stock compensation expense |  |  |  |  | $ 2,613,000 | $ 1,653,000 | $ 924,000 |  |  |  |  |
Employee stock options granted (in shares) |  |  |  | 0 | 300,000 | 750,000 | 0 |  |  |  |  |
Restricted Shares |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Restricted shares of common stock awarded (in shares) |  |  |  |  | 5,000 | 0 | 0 |  |  |  |  |
Weighted average fair value (in dollars per share) |  |  |  |  | $ 31.95 | $ 0.00 | $ 0.00 |  |  |  |  |
Total stock compensation expense |  |  |  |  | $ 137,000 | $ 264,000 | $ 150,000 |  |  |  |  |
Unrecognized compensation costs |  |  |  |  | 172,000 | 149,000 |  |  |  |  |  |
Employee Stock Option |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Total stock compensation expense |  |  |  |  | 1,617,000 | 616,000 | $ 0 |  |  |  |  |
Unrecognized compensation costs |  |  |  |  | $ 2,174,000 | $ 2,030,000 |  |  |  |  |  |
Employee stock options granted (in shares) |  |  |  |  | 300,000 | 750,000 |  |  |  |  |  |
Number of shares available for issuance (in shares) |  |  |  | 0 | 675,000 | 750,000 | 0 |  |  |  |  |
2015 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of shares authorized to be repurchased (up to) (in shares) |  |  |  |  |  |  |  |  |  | 1,250,000 |  |
2015 Plan | Restricted Shares |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting period |  |  | 2 years 6 months |  |  |  |  |  |  |  |  |
Restricted shares of common stock awarded (in shares) |  |  | 5,000 |  |  |  |  |  |  |  |  |
Weighted average fair value (in dollars per share) |  |  | $ 31.95 |  |  |  |  |  |  |  |  |
2015 Plan | Employee Stock Option |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of shares available for issuance (in shares) |  |  |  |  | 557,500 |  |  |  |  |  |  |
2018 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Shares issued (in dollars per share) | $ 33.60 |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  |  |  | $ 33.80 |  |  |  |  |  |  |
2018 Plan | Employee Stock Option |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Weighted average grant date fair value (in dollars per share) |  |  |  |  | 7.40 |  |  |  |  |  |  |
2016 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Shares issued (in dollars per share) |  | $ 27.15 |  |  |  |  |  |  |  |  |  |
Period of consecutive trading days |  | 20 days |  |  |  |  |  |  |  |  |  |
Period following an executive's termination of employment without cause |  | 18 months |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  |  |  | $ 33.80 |  |  |  |  |  |  |
2016 Plan | Employee Stock Option |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Weighted average grant date fair value of option grant (in dollars per share) |  |  |  |  |  | $ 3.53 |  |  |  |  |  |
Minimum | 2015 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting period |  |  |  |  | 1 year |  |  |  |  |  |  |
Maximum | 2015 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Vesting period |  |  |  |  | 6 years |  |  |  |  |  |  |
Maximum | 2018 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  |  |  | $ 35.00 |  |  |  |  |  |  |
Maximum | 2016 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Share price (in dollars per share) |  |  |  |  | $ 60.00 |  |  |  |  |  |  |
Chief Executive Officer | 2018 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Employee stock options granted (in shares) | 210,000 |  |  |  |  |  |  |  |  |  |  |
Chief Executive Officer | 2016 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Employee stock options granted (in shares) |  | 300,000 |  |  |  |  |  |  |  |  |  |
Chief Financial Officer | 2018 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Employee stock options granted (in shares) | 90,000 |  |  |  |  |  |  |  |  |  |  |
Board of Directors Chairman | 2016 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Employee stock options granted (in shares) |  | 225,000 |  |  |  |  |  |  |  |  |  |
Shares forfeited (in shares) |  | 187,500 |  |  |  |  |  |  |  |  |  |
Unrecognized compensation expense |  |  |  |  | $ 783,000 |  |  |  |  |  |  |
Tranche One | 2018 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of option price to vest | 25.00% |  |  |  |  |  |  |  |  |  |  |
Period of consecutive trading days | 20 days |  |  |  |  |  |  |  |  |  |  |
Amount per share (in dollars per share) | $ 35.00 |  |  |  |  |  |  |  |  |  |  |
Tranche One | 2016 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of option price to vest |  | 25.00% |  |  |  |  |  |  |  |  |  |
Amount per share (in dollars per share) |  | $ 60.00 |  |  |  |  |  |  |  |  |  |
Tranche Two | 2018 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of option price to vest | 25.00% |  |  |  |  |  |  |  |  |  |  |
Period of consecutive trading days | 20 days |  |  |  |  |  |  |  |  |  |  |
Amount per share (in dollars per share) | $ 40.00 |  |  |  |  |  |  |  |  |  |  |
Tranche Two | 2016 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of option price to vest |  | 25.00% |  |  |  |  |  |  |  |  |  |
Amount per share (in dollars per share) |  | $ 75.00 |  |  |  |  |  |  |  |  |  |
Tranche Three | 2018 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of option price to vest | 25.00% |  |  |  |  |  |  |  |  |  |  |
Period of consecutive trading days | 20 days |  |  |  |  |  |  |  |  |  |  |
Amount per share (in dollars per share) | $ 45.00 |  |  |  |  |  |  |  |  |  |  |
Tranche Three | 2016 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of option price to vest |  | 25.00% |  |  |  |  |  |  |  |  |  |
Amount per share (in dollars per share) |  | $ 90.00 |  |  |  |  |  |  |  |  |  |
Tranche Four | 2018 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of option price to vest | 25.00% |  |  |  |  |  |  |  |  |  |  |
Period of consecutive trading days | 20 days |  |  |  |  |  |  |  |  |  |  |
Amount per share (in dollars per share) | $ 50.00 |  |  |  |  |  |  |  |  |  |  |
Tranche Four | 2016 Plan |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of option price to vest |  | 25.00% |  |  |  |  |  |  |  |  |  |
Amount per share (in dollars per share) |  | $ 105.00 |  |  |  |  |  |  |  |  |  |

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