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STOCK-BASED COMPENSATION - Narrative (Details) $ / shares in Units, shares in Thousands, $ in Thousands | 1 Months Ended | 3 Months Ended | 6 Months Ended
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Jun. 30, 2021 USD ($) tranche shares | Feb. 28, 2021 USD ($) $ / shares shares | Jun. 30, 2021 USD ($) tranche shares | Jun. 30, 2020 USD ($) | Jun. 30, 2021 USD ($) tranche shares | Jun. 30, 2020 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Aggregate intrinsic value, exercised |  |  |  |  | $ 17,970 |
Unrecognized compensation cost, options | $ 23,972 |  | $ 23,972 |  | 23,972 |
Unrecognized compensation cost | $ 54,755 |  | 54,755 |  | 54,755 |
Fair market value of share price (in usd per share) | $ / shares |  | $ 38.08 |  |  |  |
Payments for repurchase of stock options |  |  |  |  | 7,335 | $ 0
Compensation expense |  |  | $ 2,907 | $ 1,681 | 5,458 | $ 2,835
Options repurchased |  |  |  |  | 7,335 |
Common stock repurchased and retired |  |  |  |  | 868 |
Additional Paid-in Capital |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Options repurchased |  |  |  |  | 7,335 |
Common stock repurchased and retired |  |  |  |  | $ 868 |
Tender Offer |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Sale of stock, price per share (in usd per share) | $ / shares |  | $ 59.77 |  |  |  |
Payments for repurchase of stock options |  | $ 13,479 |  |  |  |
Compensation expense |  | $ 5,275 |  |  |  |
Options recycled back into option pool (in shares) | shares |  | 220 |  |  |  |
Common stock repurchased and retired (in shares) | shares |  | 23 |  |  |  |
Common stock repurchased and retired |  | $ 868 |  |  |  |
Tender Offer | Additional Paid-in Capital |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Options repurchased |  | $ 7,335 |  |  |  |
Stock options |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Unrecognized compensation cost, weighted-average period of recognition |  |  |  |  | 2 years |
Number of options available for grant (in shares) | shares | 114 |  | 114 |  | 114 |
Restricted Stock Units (RSUs) |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Equity instruments other than options, grants in period (in shares) | shares |  |  |  |  | 561 |
Unrecognized compensation cost, weighted-average period of recognition |  |  |  |  | 4 years |
Unrecognized compensation expense, excluding options | $ 30,783 |  | $ 30,783 |  | $ 30,783 |
Performance Shares |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Unrecognized compensation expense, excluding options | $ 100,543 |  | $ 100,543 |  | $ 100,543 |
Performance Shares | Minimum |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Unrecognized compensation cost, weighted-average period of recognition | 1 year |  |  |  |  |
Performance Shares | Maximum |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Unrecognized compensation cost, weighted-average period of recognition | 7 years |  |  |  |  |
Performance Shares | Founders |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Equity instruments other than options, grants in period (in shares) | shares | 1,800 |  |  |  |  |
Settlement period after vesting | 1 year |  |  |  |  |
Award vesting percentage | 25.00% |  |  |  |  |
Award service period | 10 years |  |  |  |  |
Number of tranches | tranche | 10 |  | 10 |  | 10 |
Compensation expense |  |  |  |  | $ 0 |
2011 Equity Incentive Plan |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Share-based compensation arrangement, number of shares authorized (in shares) | shares | 10,113 |  | 10,113 |  | 10,113 |
Vesting period |  |  |  |  | 4 years |
Share-based compensation, term of award |  |  |  |  | 10 years |
Incentive stock options, minimum exercise price, percent |  |  |  |  | 100.00% |
2011 Equity Incentive Plan | Principal Owner |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Incentive stock options, minimum exercise price, percent |  |  |  |  | 110.00% |

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