SHAREHOLDERS’ EQUITY AND SHARE-BASED COMPENSATION - Stock Repurchase Plan & Share-Based Compensation (Details) | May 15, 2018$ / sharesshares | Sep. 30, 2019USD ($)$ / sharesshares | Sep. 30, 2018USD ($)$ / sharesshares | Sep. 30, 2019USD ($)component$ / sharesshares | Sep. 30, 2018USD ($)$ / sharesshares | Dec. 31, 2018shares |
Share Repurchase Program | | | | | | |
Authorized amount (in dollars) | $ | | $ 104,000,000 | | $ 104,000,000 | | |
Capacity available to repurchase common stock under senior secured term loan (in dollars) | $ | | 443,000,000 | | 443,000,000 | | |
Share-Based Compensation | | | | | | |
Share-based compensation expense | $ | | 2,800,000 | $ 2,000,000 | 8,284,000 | $ 6,150,000 | |
Estimated unrecognized compensation costs (in dollars) | $ | | $ 11,700,000 | | $ 11,700,000 | | |
Weighted average remaining requisite service period for stock options over which unrecognized compensation costs would be recognized | | | | 1 year 7 months 13 days | | |
Outstanding (in shares) | | 1,494,491 | | 1,494,491 | | 1,440,566 |
Weighted average fair value of stock options granted and total intrinsic value of stock options exercised | | | | | | |
Weighted average grant date fair value of stock options granted per share (in usd per share) | $ / shares | | | | $ 0 | $ 16.27 | |
Intrinsic value of options exercised | $ | | | | $ 52,000 | $ 4,584,000 | |
Grant date fair value of stock options that vested | $ | | | | $ 3,014,000 | $ 1,598,000 | |
Employee and non-employee stock options | | | | | | |
Share-Based Compensation | | | | | | |
Stock options granted (in shares) | | | | 0 | 272,000 | |
Performance criteria achieved (in shares) | | | | 227,849 | | |
Weighted average exercise price of stock options granted (in usd per share) | $ / shares | | | | | $ 25.06 | |
Employee and non-employee stock options | Service-Based | | | | | | |
Share-Based Compensation | | | | | | |
Outstanding (in shares) | | 438,000 | | 438,000 | | |
Employee and non-employee stock options | Service-Based | Minimum | | | | | | |
Share-Based Compensation | | | | | | |
Vesting period | | | | 3 years | | |
Employee and non-employee stock options | Service-Based | Maximum | | | | | | |
Share-Based Compensation | | | | | | |
Vesting period | | | | 4 years | | |
Expiration term | | | | 10 years | | |
Employee and non-employee stock options | Market-Based | | | | | | |
Share-Based Compensation | | | | | | |
Outstanding (in shares) | | 584,000 | | 584,000 | | |
Number of components of an award | component | | | | 2 | | |
Allowable performance period before expiration date | | | | 3 years | | |
Employee and non-employee stock options | Market-Based | Minimum | | | | | | |
Share-Based Compensation | | | | | | |
Vesting period | | | | 3 years | | |
Expiration term | | | | 10 years | | |
Employee and non-employee stock options | Market-Based | Maximum | | | | | | |
Share-Based Compensation | | | | | | |
Vesting period | | | | 4 years | | |
Employee and non-employee stock options | Market-Based, ordinary performance | Minimum | | | | | | |
Share-Based Compensation | | | | | | |
Percentage of compounded annual gain of stock price over exercise price required for the award to vest | | | | 20.00% | | |
Employee and non-employee stock options | Market-Based, extraordinary performance | Minimum | | | | | | |
Share-Based Compensation | | | | | | |
Percentage of compounded annual gain of stock price over exercise price required for the award to vest | | | | 25.00% | | |
Employee and non-employee stock options | Performance-Based | | | | | | |
Share-Based Compensation | | | | | | |
Outstanding (in shares) | | 472,000 | | 472,000 | | |
Employee and non-employee stock options | Performance-Based | Minimum | | | | | | |
Share-Based Compensation | | | | | | |
Allowable performance period before expiration date | | | | 10 years | | |
Attainment above threshold performance levels, vesting percentage | | | | 50.00% | | |
Employee and non-employee stock options | Performance-Based | Maximum | | | | | | |
Share-Based Compensation | | | | | | |
Attainment above threshold performance levels, vesting percentage | | | | 200.00% | | |
Employee and non-employee stock options | Performance-Based, Vesting Period One | | | | | | |
Share-Based Compensation | | | | | | |
Vesting percentage | | | | 25.00% | | |
Employee and non-employee stock options | Performance-Based, Vesting Period Two | | | | | | |
Share-Based Compensation | | | | | | |
Vesting percentage | | | | 25.00% | | |
Employee and non-employee stock options | Performance-Based, Vesting Period Three | | | | | | |
Share-Based Compensation | | | | | | |
Vesting percentage | | | | 25.00% | | |
Employee and non-employee stock options | Performance-Based, Vesting Period Four | | | | | | |
Share-Based Compensation | | | | | | |
Vesting percentage | | | | 25.00% | | |
Restricted Stock And Restricted Stock Units (RSUs) | | | | | | |
Share-Based Compensation | | | | | | |
Restricted shares and restricted share units outstanding (in shares) | | 669,708 | | 669,708 | | 485,806 |
Restricted share units granted (in shares) | | | | 401,458 | | |
Restricted share units granted, weighted average grant date fair value (in usd per share) | $ / shares | | | | $ 24.61 | | |
Restricted Stock And Restricted Stock Units (RSUs) | Service-Based | | | | | | |
Share-Based Compensation | | | | | | |
Restricted shares and restricted share units outstanding (in shares) | | 520,000 | | 520,000 | | |
Restricted Stock And Restricted Stock Units (RSUs) | Service-Based | Minimum | | | | | | |
Share-Based Compensation | | | | | | |
Vesting period | | | | 2 years | | |
Restricted Stock And Restricted Stock Units (RSUs) | Service-Based | Maximum | | | | | | |
Share-Based Compensation | | | | | | |
Vesting period | | | | 4 years | | |
Restricted Stock And Restricted Stock Units (RSUs) | Performance-Based | | | | | | |
Share-Based Compensation | | | | | | |
Restricted shares and restricted share units outstanding (in shares) | | 150,000 | | 150,000 | | |
Restricted Stock And Restricted Stock Units (RSUs) | Performance-Based | Maximum | | | | | | |
Share-Based Compensation | | | | | | |
Attainment above threshold performance levels, vesting percentage | | | | 225.00% | | |
Restricted Stock And Restricted Stock Units (RSUs) | Performance-Based, Vesting Period One | | | | | | |
Share-Based Compensation | | | | | | |
Vesting percentage | | | | 33.00% | | |
Restricted Stock And Restricted Stock Units (RSUs) | Performance-Based, Vesting Period Two | | | | | | |
Share-Based Compensation | | | | | | |
Vesting percentage | | | | 33.00% | | |
Restricted Stock And Restricted Stock Units (RSUs) | Performance-Based, Vesting Period Three | | | | | | |
Share-Based Compensation | | | | | | |
Vesting percentage | | | | 33.00% | | |
Share Repurchase Program, Current | | | | | | |
Share Repurchase Program | | | | | | |
Number of shares of common stock authorized to be purchased (in shares) | 4,300,000 | | | | | |
Percentage of outstanding shares authorized to be repurchased | 25.00% | | | | | |
Minimum purchase price authorized (in usd per share) | $ / shares | $ 1 | | | | | |
Maximum purchase price authorized (in usd per share) | $ / shares | $ 500 | | | | | |
Period that shares may be repurchased, from the date of approval | 5 years | | | | | |
Remaining number of shares available for repurchase under the plan (in shares) | | 2,700,000 | | 2,700,000 | | |
Share Repurchase Programs | | | | | | |
Share Repurchase Program | | | | | | |
Number of shares of common stock purchased (in shares) | | 300,000 | 21,000 | 600,000 | 800,000 | |
Average purchase price per share (in usd per share) | $ / shares | | $ 20.24 | $ 30.93 | $ 21.03 | $ 27.48 | |
Black-Scholes | | | | | | |
Assumptions used to determine the fair value of options as of the grant date | | | | | | |
Expected dividend yield | | | | | 0.00% | |
Black-Scholes | Minimum | | | | | | |
Assumptions used to determine the fair value of options as of the grant date | | | | | | |
Risk-free interest rate (%) | | | | | 2.66% | |
Expected stock price volatility (%) | | | | | 70.31% | |
Expected option life (in years) | | | | | 6 years | |
Fair value | $ / shares | | | 16.17 | | $ 16.17 | |
Black-Scholes | Maximum | | | | | | |
Assumptions used to determine the fair value of options as of the grant date | | | | | | |
Risk-free interest rate (%) | | | | | 2.98% | |
Expected stock price volatility (%) | | | | | 71.86% | |
Expected option life (in years) | | | | | 6 years 3 months | |
Fair value | $ / shares | | | 19.06 | | $ 19.06 | |
Binomial | | | | | | |
Assumptions used to determine the fair value of options as of the grant date | | | | | | |
Expected dividend yield | | | | | 0.00% | |
Binomial | Minimum | | | | | | |
Assumptions used to determine the fair value of options as of the grant date | | | | | | |
Risk-free interest rate (%) | | | | | 1.64% | |
Expected stock price volatility (%) | | | | | 71.81% | |
Expected option life (in years) | | | | | 2 years 6 months 22 days | |
Fair value | $ / shares | | | 14.67 | | $ 14.67 | |
Binomial | Maximum | | | | | | |
Assumptions used to determine the fair value of options as of the grant date | | | | | | |
Risk-free interest rate (%) | | | | | 2.83% | |
Expected stock price volatility (%) | | | | | 71.86% | |
Expected option life (in years) | | | | | 4 years 3 months 26 days | |
Fair value | $ / shares | | | $ 18.28 | | $ 18.28 | |