STOCKHOLDERS' EQUITY - Narrative (Detail) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2016
Limited Partners' Capital Account [Line Items]
Fair value of stock awards vested		$ 41,000		$ 5,892,000
Stock Options
Limited Partners' Capital Account [Line Items]
Stock-based compensation expense		0	$ 0	0	$ 0
Aggregate intrinsic value of options exercised		0		296,000
Restricted Stock, Restricted Stock Units And Performance Stock Units
Limited Partners' Capital Account [Line Items]
Stock-based compensation expense		1,898,000	1,858,000	5,175,000	5,084,000
Restricted Stock
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation expense		84,000		$ 84,000
Restricted Stock | Non Employee Director
Limited Partners' Capital Account [Line Items]
Options, vesting period				3 years
Restricted Stock Unit
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation expense		4,684,000		$ 4,684,000
Performance Stock Unit
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation expense		5,196,000		$ 5,196,000
Weighted average | Restricted Stock
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation, weighted average period				2 years 7 months 6 days
Weighted average | Restricted Stock Unit
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation, weighted average period				1 year 10 months 24 days
Weighted average | Performance Stock Unit
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation, weighted average period				1 year 9 months 18 days
2016 Plan
Limited Partners' Capital Account [Line Items]
Options granted, term				10 years
2016 Plan | Minimum
Limited Partners' Capital Account [Line Items]
Options, vesting period				1 year
2016 Plan | Maximum
Limited Partners' Capital Account [Line Items]
Options, vesting period				4 years
Amended and Restated 1997 Employee Stock Purchase Plan
Limited Partners' Capital Account [Line Items]
Stock-based compensation expense		$ 67,000	$ 40,000	$ 171,000	$ 134,000
Class A Common Stock | Subsequent Event
Limited Partners' Capital Account [Line Items]
Number of shares issued	2,703,000
Public offering price (in dollars per share)	$ 56.00
Net proceeds	$ 144,711,000
Class A Common Stock | 2016 Plan
Limited Partners' Capital Account [Line Items]
Common stock, authorized shares						2,250,000
Number of shares available for future grant		1,102,000		1,102,000
Class A Common Stock | 2006 Incentive Plan
Limited Partners' Capital Account [Line Items]
Common stock, additional authorized shares						2,723,000