INCOME TAXES (Reconciliation of Provision for Income Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective tax rate reconciliation [Abstract]
Expected federal income tax provision at statutory rate									$ 59,643	$ 57,770	$ 47,832
State income taxes, net of federal benefit									10,312	4,776	3,638
Foreign income taxes, net effect									(315)	(3,540)	(31)
Increase (decrease) in valuation allowance									1,214	3,624	(103)
Tax rate changes									141	(7,340)	283
Research credits									(15,373)	(20,547)	(920)
Excess tax benefit									(14,227)	(7,010)	0
Tax reserves									1,870	12,646	(150)
Other adjustments									2,416	1,984	1,042
Income tax expense	$ 26,060	$ 14,247	$ 1,863	$ 3,511	$ 4,487	$ 20,990	$ 3,611	$ 13,275	$ 45,681	$ 42,363	$ 51,591