SEGMENT REPORTING - Summary of Financial Information by Segment (Details) - USD ($) $ 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
Segment Reporting Information [Line Items]
Revenues	$ 302,294	$ 297,264	$ 264,300	$ 277,939	$ 287,579	$ 269,482	$ 237,169	$ 250,843	$ 1,141,797	$ 1,045,073	$ 924,137
Net revenues	172,005	173,397	152,290	175,554	156,901	141,790	150,822	173,960	673,246	623,473	611,571
Consolidated gross margin	95,299	$ 96,639	$ 81,181	$ 105,497	81,682	$ 60,594	$ 77,348	$ 105,846	378,616	325,470	335,165
Consolidated operating profit									142,455	18,118	102,256
Consolidated expenditures for long-lived assets									14,612	14,033	8,717
Total gross loans receivable	665,828				571,531				665,828	571,531
U.S.
Segment Reporting Information [Line Items]
Revenues									913,506	853,141	737,729
Net revenues									521,401	504,530	470,238
Consolidated gross margin									302,952	284,828	267,215
Consolidated operating profit									99,152	1,117	51,459
Consolidated expenditures for long-lived assets									12,733	11,105	7,406
Total gross loans receivable	363,453				361,473				363,453	361,473
Canada
Segment Reporting Information [Line Items]
Revenues									228,291	191,932	186,408
Net revenues									151,845	118,943	141,333
Consolidated gross margin									75,664	40,642	67,950
Consolidated operating profit									43,303	17,001	50,797
Consolidated expenditures for long-lived assets									1,879	2,928	$ 1,311
Total gross loans receivable	$ 302,375				$ 210,058				$ 302,375	$ 210,058