NET INCOME PER COMMON SHARE - Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015
Numerator:
Net income	$ 26,428	$ 36,962	$ 43,440	$ 31,474	$ 19,249	$ 22,818	$ 10,814	$ 5,959	$ 138,304	$ 58,840	$ 103,885	$ 103,885
Adjustment for Basic EPS:
Earnings allocated to unvested shareholders									(1,106)	(690)		(1,638)
Adjusted net income									$ 137,198	$ 58,150		$ 102,247
Denominator:
Weighted average common shares outstanding – Basic									46,959,775	46,849,588	46,725,289	46,725,289
Effect of dilutive shares:
Common stock equivalents arising from stock options and ESPP									1,334	1,956		2,611
Restricted stock awards and units and performance units									34,353	45,222		77,294
Weighted average common shares outstanding – Diluted									46,995,462	46,896,766	46,805,194	46,805,194
Basic	$ 0.56	$ 0.78	$ 0.92	$ 0.66	$ 0.40	$ 0.48	$ 0.23	$ 0.13	$ 2.92	$ 1.24	$ 2.19	$ 2.19
Diluted	$ 0.56	$ 0.78	$ 0.92	$ 0.66	$ 0.40	$ 0.48	$ 0.23	$ 0.13	$ 2.92	$ 1.24	$ 2.18	$ 2.18