EARNINGS PER SHARE - Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Basic, numerator:
Net income	$ 23,914	$ 29,404	$ 15,880	$ 1,902	$ (5,549)	$ 16,270	$ 24,376	$ 4,888	$ 71,100	$ 39,985	$ 67,262
Effect of unvested restricted stock unit awards										(22)	(150)
Adjusted net income									$ 71,100	$ 39,963	$ 67,112
Basic, denominator:
Weighted-average shares	25,427,449	25,470,094	25,463,559	25,390,377	25,490,393	25,527,982	25,554,286	25,570,415	25,410,232	25,535,529	25,679,736
Earnings per common share (in dollars per share)	$ 0.94	$ 1.15	$ 0.62	$ 0.07	$ (0.22)	$ 0.64	$ 0.95	$ 0.19	$ 2.80	$ 1.56	$ 2.61
Diluted, numerator:
Net income	$ 23,914	$ 29,404	$ 15,880	$ 1,902	$ (5,549)	$ 16,270	$ 24,376	$ 4,888	$ 71,100	$ 39,985	$ 67,262
Effect of unvested restricted stock unit awards										(21)	(145)
Adjusted net income									$ 71,100	$ 39,964	$ 67,117
Diluted, denominator:
Weighted-average shares	25,427,449	25,470,094	25,463,559	25,390,377	25,490,393	25,527,982	25,554,286	25,570,415	25,410,232	25,535,529	25,679,736
Effect of dilutive securities									1,012,291	914,526	1,019,095
Adjusted weighted-average shares and assumed conversions	26,734,287	26,592,457	26,217,957	26,246,800	25,490,393	26,416,595	26,431,592	26,512,349	26,422,523	26,450,055	26,698,831
Earnings per common share (in dollars per share)	$ 0.89	$ 1.11	$ 0.61	$ 0.07	$ (0.22)	$ 0.62	$ 0.92	$ 0.18	$ 2.69	$ 1.51	$ 2.51