GOODWILL, TRADE NAMES, AND OTHER INTANGIBLE ASSETS - Acquired Intangible Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 78,572	$ 64,372
Accumulated Amortization	34,427	29,541
Net Carrying Amount	44,145	34,831
Trade names, indefinite-lived	5,900	5,900
Databases
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	30,530	30,530
Accumulated Amortization	17,612	15,322
Net Carrying Amount	12,918	15,208
Customer relationships
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	47,738	33,538
Accumulated Amortization	16,558	14,007
Net Carrying Amount	31,180	19,531
Non-compete agreements
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	304	304
Accumulated Amortization	257	212
Net Carrying Amount	$ 47	$ 92