EARNINGS PER SHARE - Computation of basic and diluted earnings per share (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
3 Months Ended 12 Months Ended
Jun. 30, 2020
Mar. 31, 2020
Dec. 31, 2019
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2018
Numerator:                      
Net income $ 92,618 $ 103,722 $ 85,811 $ 98,146 $ 70,895 $ 88,300 $ 77,796 $ 85,703 $ 380,297 $ 322,694 $ 196,290
Denominator:                      
Weighted-average shares used in computing basic net income per share (in shares)                 65,427 71,435 77,179
Weighted-average shares used in computing diluted net income per share (in shares)                 65,514 71,602 78,331
Net income per share of common stock:                      
Basic (in dollars per share) $ 1.45 $ 1.60 $ 1.32 $ 1.44 $ 1.01 $ 1.25 $ 1.09 $ 1.16 $ 5.81 $ 4.52 $ 2.54
Diluted (in dollars per share) $ 1.45 $ 1.60 $ 1.32 $ 1.43 $ 1.01 $ 1.25 $ 1.09 $ 1.16 $ 5.80 $ 4.51 $ 2.51
Stock options                      
Denominator:                      
Dilutive potential common shares (in shares)                 30 87 1,074
Restricted stock units                      
Denominator:                      
Dilutive potential common shares (in shares)                 57 80 78