ACQUISITION - Estimated fair values of acquired assets and liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Purchase Allocation
Goodwill	$ 299,075		$ 299,075		$ 300,337
Operating revenues	1,392,929	$ 948,973	2,728,003	$ 1,778,186
Operating income (loss)	137,346	$ 74,299	232,274	$ 106,490
MoLo Solutions, LLC
Purchase Allocation
Accounts receivable	134,622		134,622
Prepaid expenses	468		468
Property and equipment	2,309		2,309
Operating lease right-of use assets	844		844
Intangible assets	76,900		76,900
Other assets	170		170
Total identifiable assets acquired	215,313		215,313
Accounts payable	94,461		94,461
Accrued expenses and other current liabilities	2,973		2,973
Operating lease liabilities	983		983
Total liabilities	98,417		98,417
Total identifiable net assets	116,896		116,896
Goodwill	212,707		212,707
Net assets acquired	$ 329,603		$ 329,603