RECENT ACCOUNTING PRONOUNCEMENTS Revenue Recognition - Effect on Statement of Consolidated Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Services revenue	$ 928,144	$ 840,687
Total revenues	1,903,467	1,736,983
Cost of services	787,238	702,900
Selling, general and administrative expenses	208,624	201,095
Earnings from continuing operations before income taxes	48,100	60,622
Provision for income taxes	14,168	22,086
Earnings from continuing operations	33,932	38,536
Net earnings	$ 33,505	$ 38,406
Earnings per common share - Basic
Continuing operations	$ 0.65	$ 0.73
Earnings per common share - Diluted
Continuing operations	0.64	0.72
Net earnings	$ 0.63	$ 0.72
Correction of prior period error		$ 11,000
Accounting Standards Update 2014-09 \| As Previously Reported
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Services revenue		851,867
Total revenues		1,748,163
Cost of services		714,080
Selling, general and administrative expenses		201,761
Earnings from continuing operations before income taxes		59,956
Provision for income taxes		21,677
Earnings from continuing operations		38,279
Net earnings		$ 38,149
Earnings per common share - Basic
Continuing operations		$ 0.72
Earnings per common share - Diluted
Continuing operations		0.71
Net earnings		$ 0.71
Accounting Standards Update 2014-09 \| New Revenue Standard Adjustment
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Services revenue		$ (11,180)
Total revenues		(11,180)
Cost of services		(11,180)
Selling, general and administrative expenses		(666)
Earnings from continuing operations before income taxes		666
Provision for income taxes		409
Earnings from continuing operations		257
Net earnings		$ 257
Earnings per common share - Basic
Continuing operations		$ 0.01
Earnings per common share - Diluted
Continuing operations		0.01
Net earnings		$ 0.01

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