SEGMENT REPORTING - Long-lived Assets by Geographic Areas (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Revenues from External Customers and Long-Lived Assets [Line Items]
Total assets	$ 4,354,299	$ 4,131,520
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total assets	3,629,056	3,447,811
Canada and other foreign
Revenues from External Customers and Long-Lived Assets [Line Items]
Total assets	$ 725,243	$ 683,709