CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement Of Income And Comprehensive Income [Abstract]
NET INCOME	$ 51,687	$ 38,155
OTHER COMPREHENSIVE INCOME, NET OF TAX:
Unrealized (loss) gain on available-for-sale securities, net of tax of $17 and $525, respectively	(58)	1,855
Amortization of prior service cost and actuarial loss for retirement plan included in net periodic pension costs, net of tax of $335 and $182, respectively	1,174	638
Change in cumulative foreign currency translation adjustment	(106)	(33)
TOTAL OTHER COMPREHENSIVE INCOME	1,010	2,460
COMPREHENSIVE INCOME	$ 52,697	$ 40,615