CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement Of Income And Comprehensive Income [Abstract]
NET INCOME	$ 38,155	$ 31,474
OTHER COMPREHENSIVE INCOME, NET OF TAX:
Unrealized gain on available-for-sale securities, net of tax of $525 and $13, respectively	1,855	47
Amortization of prior service cost and actuarial loss for retirement plan included in net periodic pension costs, net of tax of $182 and $175, respectively	638	634
Change in cumulative foreign currency translation adjustment	(33)	33
TOTAL OTHER COMPREHENSIVE INCOME	2,460	714
COMPREHENSIVE INCOME	$ 40,615	$ 32,188