v3.19.3.a.u2
STOCKHOLDERS' EQUITY - compensation expense (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2019
USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Recorded stock-based compensation expense $ 4.4
Unrecognized stock-based compensation expense 13.0
Board Of Directors 2019 [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Recorded stock-based compensation expense 0.5
2019 RSU awards  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Recorded stock-based compensation expense 3.5
Unrecognized stock-based compensation expense 7.0
2018 RSU awards  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Recorded stock-based compensation expense 3.1
Unrecognized stock-based compensation expense 3.0
2018 PSU awards  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Recorded stock-based compensation expense (5.8)
2017 RSU awards  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Recorded stock-based compensation expense 1.6
2017 RSU NEO awards  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Recorded stock-based compensation expense 1.4
2019 RSU executive  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Recorded stock-based compensation expense 0.1
Unrecognized stock-based compensation expense 1.6
2019 PSU executive  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Unrecognized stock-based compensation expense 1.4
Expected to Recognize 2020  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Recorded stock-based compensation expense 8.1
Expected to Recognize 2020 | 2019 RSU awards  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Recorded stock-based compensation expense 3.5
Expected to Recognize 2020 | 2018 RSU awards  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Recorded stock-based compensation expense 3.0
Expected to Recognize 2020 | 2019 RSU executive  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Recorded stock-based compensation expense 1.1
Expected to Recognize 2020 | 2019 PSU executive  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Recorded stock-based compensation expense 0.5
Expected To Recognize 2021  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Stock-based compensation expense expected to be recognized 4.3
Expected To Recognize 2021 | 2019 RSU awards  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Stock-based compensation expense expected to be recognized 3.5
Expected To Recognize 2021 | 2019 RSU executive  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Stock-based compensation expense expected to be recognized 0.3
Expected To Recognize 2021 | 2019 PSU executive  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Stock-based compensation expense expected to be recognized 0.5
Expected To Recognize 2022  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Stock-based compensation expense expected to be recognized 0.4
Expected To Recognize 2022 | 2019 RSU executive  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Stock-based compensation expense expected to be recognized 0.2
Expected To Recognize 2022 | 2019 PSU executive  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Stock-based compensation expense expected to be recognized 0.2
Expected To Recognize 2023  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Stock-based compensation expense expected to be recognized 0.1
Expected To Recognize 2023 | 2019 PSU executive  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Stock-based compensation expense expected to be recognized 0.1
Expected To Recognize 2024  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Stock-based compensation expense expected to be recognized 0.1
Expected To Recognize 2024 | 2019 PSU executive  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Stock-based compensation expense expected to be recognized $ 0.1