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Stockholders' Equity - Additional Information (Details)			3 Months Ended	9 Months Ended	12 Months Ended
Stockholders' Equity - Additional Information (Details)	Nov. 06, 2018 $ / shares shares	Jun. 17, 2015 shares	Dec. 31, 2016	Sep. 30, 2015 shares	Sep. 30, 2019 USD ($) $ / shares shares	Sep. 30, 2018 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2016 shares	Feb. 28, 2019	Oct. 23, 2018 $ / right $ / shares shares	Mar. 07, 2018 shares	Mar. 10, 2017 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense \| $					$ 16,600,000
Weighted average period for unrecognized compensation expense expected to be recognized					2 years 3 months 18 days
Purchase of common stock (in shares)					1,686,902	2,806,364	2,845,866	3,015,374
Recognized compensation expense \| $					$ 9,637,000	$ 8,950,000	$ 5,478,000
Total intrinsic value of options exercised \| $					$ 11,100,000	$ 1,400,000	$ 1,400,000
Weighted average fair value of options granted (in dollars per share) \| $ / shares					$ 5.07	$ 4.56	$ 4.28
Aggregate intrinsic value of options \| $					$ 4,900,000	$ 8,700,000
Preferred stock, par value per share (in dollars per share) \| $ / shares					$ 0.001	$ 0.001				$ 0.001
Percentage of common stock outstanding for acquiring person under right agreement									4.90%
Series B Junior Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of preferred share purchase right for each share of common stock (in shares)										1
Preferred stock, share conversion ratio										0.001000
Preferred stock, purchase price per right (in dollars per right) \| $ / right										35.00
Preferred stock, redemption price per right (in dollars per share) \| $ / shares										$ 0.0001
ID Checker \| Closing Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized compensation expense \| $					$ 0	$ 0	$ 1,200,000
Vesting service period of shares received		27 months
Common stock issued during acquisition (in shares)		712,790
ID Checker \| ID Checker earnout shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized compensation expense \| $					$ 0	$ 400,000	$ 400,000
Earnout shares issued (in shares)				137,306				81,182
Common stock trading period			10 days
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period for unrecognized compensation expense expected to be recognized					3 years
Unrecognized compensation expense \| $					$ 2,000,000.0
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period for unrecognized compensation expense expected to be recognized					2 years 3 months 18 days
Options outstanding (in shares)					2,352,487	2,580,176	2,357,021	2,046,169
Recognized compensation expense \| $					$ 6,800,000	$ 5,900,000	$ 4,000,000.0
Unrecognized compensation expense \| $					$ 12,200,000
Senior Executive Performance RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period for unrecognized compensation expense expected to be recognized					1 year 1 month 6 days
Options outstanding (in shares)					1,722,551
Recognized compensation expense \| $					$ 1,000,000.0	1,500,000
Unrecognized compensation expense \| $					600,000
Performance Options \| Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense \| $					$ 1,700,000
Weighted average period for unrecognized compensation expense expected to be recognized					2 years 1 month 6 days
Number of common stock reserved for future grants (in shares)	800,000
Recognized compensation expense \| $					$ 700,000
Exercise price per share (in dollars per share) \| $ / shares	$ 9.50
Vesting service period of shares received	3 years
2012 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)												9,500,000
Purchase of common stock (in shares)					1,171,708
Number of common stock reserved for future grants (in shares)					807,144
2012 Plan \| RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding (in shares)					1,890,879
2012 Plan \| Senior Executive Performance RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding (in shares)					1,722,551
Prior Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase of common stock (in shares)					298,015
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)											1,000,000
Number of common stock reserved for future grants (in shares)					799,086
Shares issued under the plan (in shares)					200,914
Recognized compensation expense \| $					$ 400,000
ESPP \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount rate from market price purchase date					0.15
ESPP \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount rate from market price offering date					15.00%
ESPP \| Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized compensation expense \| $					$ 700,000	$ 1,400,000	$ 1,000,000.0
Director Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock reserved for future grants (in shares)					391,701
Director Plan \| RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)												1,500,000
Purchase of common stock (in shares)					366,870