NET INCOME (LOSS) PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net income (loss)	$ 44,204	$ 34,177	$ 22,184	$ 22,130	$ 29,573	$ 23,201	$ 15,576	$ 16,721	$ 122,695	$ 85,071	$ (3,465)
Denominator:
Denominator for basic net income (loss) per share — weighted-average outstanding shares									33,200	32,167	31,950
Effect of dilutive securities:
Stock options and restricted stock (in shares)									359	269	0
Denominator for diluted net income (loss) per share — weighted-average outstanding shares									33,559	32,436	31,950
Net income (loss) per share — basic (in dollars per share)	$ 1.24	$ 1.05	$ 0.68	$ 0.69	$ 0.92	$ 0.72	$ 0.48	$ 0.52	$ 3.70	$ 2.64	$ (0.11)
Net income (loss) per share — diluted (in dollars per share)	$ 1.22	$ 1.04	$ 0.68	$ 0.68	$ 0.91	$ 0.72	$ 0.48	$ 0.52	$ 3.66	$ 2.62	$ (0.11)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)									59	60	56
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)									87	194
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)									58	59	55
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)									1	1	1