SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, NET INCOME PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net income	$ 60,360	$ 72,793	$ 63,248	$ 85,169	$ 133,153	$ 148,417
Denominator:
Denominator for basic net income per share - weighted-average outstanding shares (in shares)	37,524		36,310		36,998	36,273
Effect of dilutive securities:
Stock options and restricted stock awards (in shares)	210		317		258	324
Denominator for diluted net income per share — weighted average outstanding shares (in shares)	37,734		36,627		37,256	36,597
Net income per share - basic (in dollars per share)	$ 1.61		$ 1.74		$ 3.60	$ 4.09
Net income per share - diluted (in dollars per share)	$ 1.60		$ 1.73		$ 3.57	$ 4.06
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	70		99		83	120
Performance Based Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	79		90		79	90