STOCKHOLDERS' EQUITY - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2016
Limited Partners' Capital Account [Line Items]
Reduction of goodwill	$ 2,618		$ 2,618
Stock Options
Limited Partners' Capital Account [Line Items]
Stock-based compensation expense	0	$ 127	0	$ 377
Aggregate intrinsic value of options exercised	7,741		19,475
Restricted Stock, Restricted Stock Units And Performance Stock Units
Limited Partners' Capital Account [Line Items]
Stock-based compensation expense	1,858	2,007	$ 5,084	5,883
Restricted Stock | Non Employee Director
Limited Partners' Capital Account [Line Items]
Options, vesting period			3 years
Restricted Stock and Restricted Stock Unit
Limited Partners' Capital Account [Line Items]
Fair value of stock awards vested	43		$ 7,764
Unrecognized stock-based compensation expense	3,852		3,852
Maximum | Performance Stock Unit
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation expense	6,009		$ 6,009
Weighted average | Restricted Stock and Restricted Stock Unit
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation, weighted average period			1 year 4 months 24 days
Weighted average | Performance Stock Unit
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation, weighted average period			10 months 24 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	$ 40	$ 34	$ 134	$ 106
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	1,399,000		1,399,000
Class A Common Stock | 2006 Incentive Plan
Limited Partners' Capital Account [Line Items]
Common stock, additional authorized shares					2,723,000
Public Stock Offering | Class A Common Stock
Limited Partners' Capital Account [Line Items]
Number of shares issued			3,565,000
Price per share (in dollars per share)	$ 29.50		$ 29.50
Sale of stock, net proceeds			$ 100,446
Unregistered Sale | Class A Common Stock
Limited Partners' Capital Account [Line Items]
Number of shares issued	59,000		59,000
Price per share (in dollars per share)	$ 44.15		$ 44.15
Sale of stock, net proceeds	$ 2,618		$ 2,618