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STOCKHOLDERS' EQUITY - Narrative (Detail) $ / shares in Units, $ in Thousands |  | 12 Months Ended
--- | --- | ---
Jan. 25, 2019 USD ($) $ / shares shares | Dec. 31, 2018 USD ($) vote $ / shares shares | Dec. 31, 2017 USD ($) vote shares | Dec. 31, 2016 USD ($) $ / shares
Limited Partners' Capital Account [Line Items] |  |  |  |
Preferred stock authorized to issue (up to) (in shares) | shares |  | 944,000 |  |
Shares issued (in shares) | shares |  | 0 | 0 |
Expected dividend yield |  |  | 0.00% | 0.00%
Total fair value of other stock awards vested |  | $ 10,529 | $ 5,706 | $ 3,238
Stock Options |  |  |  |
Limited Partners' Capital Account [Line Items] |  |  |  |
Stock-based compensation expense |  | 473 | 644 | 605
Aggregate intrinsic value of stock options exercised |  | 1,916 | 4,664 | $ 22
Market-based Performance Stock Options |  |  |  |
Limited Partners' Capital Account [Line Items] |  |  |  |
Weighted average fair value of market-based performance (in dollars per share) | $ / shares |  |  |  | $ 6.70
Expected life |  |  |  | 7 years 4 months 24 days
Risk-free interest rate |  |  |  | 2.15%
Expected volatility (as a percent) |  |  |  | 43.10%
Expected dividend yield |  |  |  | 0.00%
Restricted Stock, Restricted Stock Units and Performance Stock Units |  |  |  |
Limited Partners' Capital Account [Line Items] |  |  |  |
Stock-based compensation expense |  | 7,821 | 5,652 | $ 2,673
Restricted Stock and Restricted Stock Unit |  |  |  |
Limited Partners' Capital Account [Line Items] |  |  |  |
Unrecognized stock-based compensation expense |  | 3,024 |  |
Restricted Stock, Restricted Stock Units and Performance Stock Units |  |  |  |
Limited Partners' Capital Account [Line Items] |  |  |  |
Tax provision (benefit) |  | $ (23) |  |
Income taxes associated with stock-based compensation expense |  |  | 117 | 0
Market-based Performance Stock Units |  |  |  |
Limited Partners' Capital Account [Line Items] |  |  |  |
Weighted average fair value of market-based performance (in dollars per share) | $ / shares |  | $ 26.02 |  |
Risk-free interest rate |  | 2.39% |  |
Expected volatility (as a percent) |  | 32.70% |  |
Expected dividend yield |  | 0.00% |  |
Amended and Restated 1997 Employee Stock Purchase Plan |  |  |  |
Limited Partners' Capital Account [Line Items] |  |  |  |
Stock-based compensation expense |  | $ 150 | $ 136 | $ 115
Non-Employee Director | Restricted Stock Awards |  |  |  |
Limited Partners' Capital Account [Line Items] |  |  |  |
Options vesting period |  | 3 years |  |
Maximum | Performance Stock Units |  |  |  |
Limited Partners' Capital Account [Line Items] |  |  |  |
Unrecognized stock-based compensation expense |  | $ 4,516 |  |
Weighted Average | Restricted Stock and Restricted Stock Unit |  |  |  |
Limited Partners' Capital Account [Line Items] |  |  |  |
Unrecognized stock-based compensation expense, weighted average period |  | 1 year 1 month 6 days |  |
Weighted Average | Performance Stock Units |  |  |  |
Limited Partners' Capital Account [Line Items] |  |  |  |
Unrecognized stock-based compensation expense, weighted average period |  | 1 year 3 months |  |
2016 Incentive Plan |  |  |  |
Limited Partners' Capital Account [Line Items] |  |  |  |
Options granted period |  | 10 years |  |
2016 Incentive Plan | Minimum |  |  |  |
Limited Partners' Capital Account [Line Items] |  |  |  |
Options vesting period |  | 1 year |  |
2016 Incentive Plan | Maximum |  |  |  |
Limited Partners' Capital Account [Line Items] |  |  |  |
Options vesting period |  | 4 years |  |
Class A Common Stock |  |  |  |
Limited Partners' Capital Account [Line Items] |  |  |  |
Vote for each share held (in votes per share) | vote |  | 1 |  |
Number of shares available for future grant (in shares) | shares |  | 117,000 |  |
Class A Common Stock | 2016 Incentive Plan |  |  |  |
Limited Partners' Capital Account [Line Items] |  |  |  |
Common stock, authorized shares (in shares) | shares |  |  | 2,250,000 |
Number of shares available for future grant (in shares) | shares |  | 1,615,000 |  |
Class B Common Stock |  |  |  |
Limited Partners' Capital Account [Line Items] |  |  |  |
Vote for each share held (in votes per share) | vote |  | 10 | 10 |
Subsequent Event | Class A Common Stock | Public Stock Offering |  |  |  |
Limited Partners' Capital Account [Line Items] |  |  |  |
Sale of stock, number of shares issued (in shares) | shares | 3,565,000 |  |  |
Sale of stock, price per share (in dollars per share) | $ / shares | $ 29.50 |  |  |
Sale of stock, net proceeds | $ 100,943 |  |  |

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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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