RECENT ACCOUNTING PRONOUNCEMENTS Revenue Recognition - Effect on Statement of Consolidated Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues	$ 2,089,338	$ 1,788,028	$ 3,992,805	$ 3,525,011
Selling, general and administrative expenses	212,923	201,464	421,776	402,559
Earnings from continuing operations before income taxes	98,283	80,854	146,383	141,476
Provision for income taxes	54,764	29,459	68,932	51,545
Earnings from continuing operations	43,519	51,395	77,451	89,931
Net earnings	42,258	50,868	75,763	89,274
Comprehensive income	$ 4,861	$ 83,874	$ 55,864	$ 143,086
Earnings per common share - Basic
Continuing operations	$ 0.83	$ 0.97	$ 1.47	$ 1.70
Earnings per common share - Diluted
Continuing operations	$ 0.82	$ 0.97	$ 1.46	$ 1.69
Correction of prior period error		$ 5,000		$ 16,000
Service
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues	$ 1,072,324	865,841	$ 2,000,468	1,706,528
Cost of services	$ 906,048	729,578	$ 1,693,286	1,432,478
As Previously Reported | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues		1,793,214		3,541,377
Selling, general and administrative expenses		201,626		403,387
Earnings from continuing operations before income taxes		80,692		140,648
Provision for income taxes		29,349		51,026
Earnings from continuing operations		51,343		89,622
Net earnings		50,816		88,965
Comprehensive income		$ 83,822		$ 142,777
Earnings per common share - Basic
Continuing operations		$ 0.97		$ 1.69
Earnings per common share - Diluted
Continuing operations		$ 0.97		$ 1.68
As Previously Reported | Service | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues		$ 871,027		$ 1,722,894
Cost of services		734,764		1,448,844
New Revenue Standard Adjustment | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues		(5,186)		(16,366)
Selling, general and administrative expenses		(162)		(828)
Earnings from continuing operations before income taxes		162		828
Provision for income taxes		110		519
Earnings from continuing operations		52		309
Net earnings		52		309
Comprehensive income		$ 52		$ 309
Earnings per common share - Basic
Continuing operations		$ 0.00		$ 0.01
Earnings per common share - Diluted
Continuing operations		$ 0.00		$ 0.01
New Revenue Standard Adjustment | Service | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues				$ (16,366)
Cost of services		$ (5,186)		$ (16,366)