SEGMENT REPORTING - Total Assets by Geographical Area (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Total assets	$ 3,955,321	$ 3,738,321
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total assets	3,270,464	3,090,311
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Total assets	$ 684,857	$ 648,010