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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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The risk-free interest rate assumption that is used in valuing an option on its own shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iv) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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