STOCKHOLDERS' EQUITY - ADDITIONAL INFORMATION (Detail) - USD ($)		1 Months Ended	9 Months Ended	12 Months Ended
	Jun. 17, 2015	Jan. 31, 2016	Sep. 30, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Mar. 10, 2017	Mar. 09, 2017	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated average forfeiture rate				12.00%
Excess tax benefit on stock option exercises				$ 0	$ 0	$ 0
Unrecognized compensation expense				$ 10,700,000
Weighted average period for unrecognized compensation expense expected to be recognized (in years)				1 year 11 months 19 days
Purchase of common stock (in shares)			3,647,705	2,845,866	3,015,374	3,647,705			2,334,326
Recognized compensation expense				$ 5,478,000	$ 4,079,000	$ 3,367,000
Total intrinsic value of options exercised				$ 1,400,000	$ 3,300,000	$ 600,000
Weighted average fair value of options granted (in dollars per share)				$ 4.28	$ 3.29	$ 2.83
Aggregate intrinsic value of options				$ 15,600,000	$ 14,200,000
Percentage of earnout shares vest and eligible for resale					12.50%
Percentage of remaining earnout shares vest and eligible for resale					87.50%
Earnout Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized compensation expense				$ 412,000	$ 292,000	$ 47,000
Common stock trading period				10 days
IDchecker
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock issued during acquisition (in shares)	712,790
Earnout shares issued (in shares)		137,306	137,306		81,182
IDchecker | Closing Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized compensation expense				$ 1,200,000	$ 1,200,000	$ 300,000
Unrecognized compensation expense				$ 0
Common stock issued during acquisition (in shares)	712,790
Vesting period of shares received	27 months
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance units, threshold for partial vesting (in dollars per share)				$ 16.00
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period for unrecognized compensation expense expected to be recognized (in years)				2 years 6 months 26 days
Options outstanding (in shares)			802,917	2,357,021	2,046,169	802,917			1,101,303
Recognized compensation expense				$ 4,000,000	$ 2,700,000	$ 1,200,000
Unrecognized compensation expense				$ 9,300,000
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period for unrecognized compensation expense expected to be recognized (in years)				1 year 5 months 19 days
Recognized compensation expense				$ 1,000,000	$ 1,300,000	$ 2,200,000
Unrecognized compensation expense				$ 1,300,000
2012 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)							9,500,000	6,000,000
Purchase of common stock (in shares)				1,769,138
Number of common stock reserved for future grants (in shares)				2,464,202
2012 Plan | RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding (in shares)				1,803,165
2012 Plan | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding (in shares)				2,100,000
Recognized compensation expense				$ 400,000
Shares granted in period				2,400,000
Performance measurement period				25 days
Target stock price for full vesting (in dollars per share)				$ 20.00
Percent of RSUs converting into shares following performance shares				50.00%
RSUs converting into shares following performance period, conversion ratio				1
Performance units, percentage of RSUs vesting pending participants' continued employment				50.00%
Vesting pending participants' continued employment, required employment period				1 year
Average stock price, measurement period				20 days
RSUs aggregate fair value				$ 4,200,000
2012 Plan | Performance Shares | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance units, threshold for partial vesting (in dollars per share)				$ 16.00
Vesting percentage if stock price underperforms benchmark				25.00%
Vesting percentage if stock price exceeds benchmark				50.00%
2012 Plan | Performance Shares | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance units, threshold for partial vesting (in dollars per share)				$ 20.00
Vesting percentage if stock price underperforms benchmark				50.00%
Vesting percentage if stock price exceeds benchmark				100.00%
2012 Plan | Performance Shares | Chief Financial Officer | Former Chief Financial Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted in period				300,000
Prior Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase of common stock (in shares)				1,076,728
Director Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock reserved for future grants (in shares)				521,315
Director Plan | RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)							1,500,000	1,000,000
Purchase of common stock (in shares)				553,856