BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Effect of Adoption of Topic 606) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement
Revenues	$ 632,775	$ 588,103	$ 551,587	$ 521,333	$ 504,931	$ 468,186	$ 445,647	$ 424,148	$ 2,293,798	$ 1,842,912	$ 1,450,448
Income from operations	84,745	80,565	72,882	64,658	78,270	64,560	54,237	48,697	302,850	245,764	172,946
Provision for income taxes	10,273	12,967	11,733	3,496	18,803	369	6,864	(16,519)	38,469	9,517	101,545
Net income	$ 74,524	$ 67,002	$ 58,777	$ 60,754	$ 59,965	$ 65,618	$ 50,255	$ 64,418	$ 261,057	240,256	$ 72,760
Balance Under Revenue Guidance in Effect Before Topic 606
Income Statement
Revenues										1,843,159
Income from operations										246,011
Provision for income taxes										9,572
Net income										240,448
Topic 606 | Adjustments
Income Statement
Revenues										(247)
Income from operations										(247)
Provision for income taxes										(55)
Net income										$ (192)