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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	[1],[2]	Sep. 30, 2017	Jun. 30, 2017	[1]	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net income	$ 19,249	$ 22,818	$ 10,814	$ 5,959	$ 32,813		$ 13,520	$ 47,187		$ 10,365	$ 58,840	$ 103,885	$ 48,070	$ 48,070
Adjustment for Basic EPS:
Earnings allocated to unvested shareholders											(690)	(1,638)		(734)
Adjusted net income											$ 58,150	$ 102,247		$ 47,336
Denominator:
Weighted average common shares outstanding – Basic											46,849,588	46,725,289	46,408,460	46,408,460
Effect of dilutive shares:
Common stock equivalents arising from stock options and ESPP											1,956	2,611		5,398
Restricted stock awards and units and performance units											45,222	77,294		122,122
Weighted average common shares outstanding – Diluted											46,896,766	46,805,194	46,535,980	46,535,980
Basic	$ 0.40	$ 0.48	$ 0.23	$ 0.13	$ 0.70		$ 0.28	$ 0.99		$ 0.22	$ 1.24	$ 2.19	$ 1.02	$ 1.02
Diluted	$ 0.40	$ 0.48	$ 0.23	$ 0.13	$ 0.69		$ 0.28	$ 0.99		$ 0.22	$ 1.24	$ 2.18	$ 1.02	$ 1.02

[1] Prior to the adoption of ASC 606 on January 1, 2018, the Company recorded as revenue the receipt of the semi-annual license fee payment of $45.0 million from SDC in the second and fourth quarters.

[2] The enactment of the Tax Cuts and Jobs Act in December 2017 resulted in a one-time charge of $11.5 million in the fourth quarter.