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STOCKHOLDERS' EQUITY - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2016
Stock Options
Limited Partners' Capital Account [Line Items]
Stock-based compensation expense	$ 127	$ 158	$ 377	$ 505
Aggregate intrinsic value of options exercised	361		1,916
Unrecognized stock-based compensation expense	96		96
Restricted Stock, Restricted Stock Units, and Performance-Based Stock Units
Limited Partners' Capital Account [Line Items]
Stock-based compensation expense	2,007	1,684	$ 5,883	4,183
Restricted Stock Awards | 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]
Total fair value of other stock awards vested	207		$ 9,826
Unrecognized stock-based compensation expense	3,680		$ 3,680
Market-based Performance Stock Options
Limited Partners' Capital Account [Line Items]
Weighted average fair value (in dollars per share)			$ 26.02
Risk free interest rate			2.39%
Expected volatility			32.70%
Dividend yield			0.00%
Maximum | Performance-Based Stock Units
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation expense	5,766		$ 5,766
Weighted Average | Stock Options
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation expense, weighted average period			1 month
Weighted Average | Restricted Stock and Restricted Stock Unit
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation expense, weighted average period			1 year 4 months 4 days
Weighted Average | Performance-Based Stock Units
Limited Partners' Capital Account [Line Items]
Unrecognized stock-based compensation expense, weighted average period			1 year
2016 Plan
Limited Partners' Capital Account [Line Items]
Options granted period			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	$ 34	$ 31	$ 106	$ 96
Class A Common Stock | 2016 Plan
Limited Partners' Capital Account [Line Items]
Common stock, authorized shares (in shares)					2,250
Number of shares available for future grant (in shares)	1,615,000		1,615,000
Class A Common Stock | 2006 Incentive Plan
Limited Partners' Capital Account [Line Items]
Common stock, additional authorized shares (in shares)					2,723,000

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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Number of additional shares authorized for issuance under an established share-based compensation plan.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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