ACQUISITIONS AND DIVESTITURES Pro Forma (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Business Acquisition [Line Items]
Revenues	$ 3,357,202	$ 3,467,362	$ 3,502,918	$ 3,142,585	$ 3,152,882	$ 3,316,665	$ 3,288,262	$ 2,994,267	$ 13,470,067	$ 12,752,076	$ 11,359,113
Business acquisition, pro forma revenue											12,010,326
Income from operations	187,728	203,337	200,382	156,971	155,113	176,355	182,476	168,706	748,418	682,650	675,320
Business acquisition, pro forma operating income											678,873
Net income	112,947	124,981	118,596	93,187	92,952	107,737	111,872	103,343	449,711	415,904	593,804
Business acquisition, pro forma net income											592,976
Phoenix
Business Acquisition [Line Items]
Business acquisition, pro forma revenue											692,836
Business acquisition, pro forma operating income											24,131
Business acquisition, pro forma net income											11,976
Eliminate personnel costs from purchased transportation and related services											(24,422)
Eliminate personnel costs from selling, general, and administrative services											(50,065)
Reclassify costs to personnel expenses											74,487
Contractual changes in compensation											(5,080)
Additional amortization expense on identifiable intangible assets											13,555
Rent expense for new lease agreements											280
Depreciation on acquired building											123
Incremental interest expense											(2,127)
Additional bonus paid by sellers											(1,400)
Third party advisory fees paid by sellers											(582)
Elimination of variable interest entities not acquired											215
Tax effect											(1,487)
T-Chek
Business Acquisition [Line Items]
Business divestiture, pro forma revenue											(41,623)
Business divestiture, pro forma operating income											(20,578)
Business divestiture, pro forma net income											$ (12,804)