CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
NET INCOME	$ 46,109	$ 40,500	$ 138,337	$ 79,470
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX:
Unrealized (loss) gain on available-for-sale securities, net of tax of $1, $177, $10 and $97, respectively	(3)	(626)	(35)	342
Amortization of prior service cost and actuarial loss for retirement plan included in net periodic pension costs, net of tax of $334, $181, $1004 and $543, respectively	1,174	639	3,522	1,917
Change in cumulative foreign currency translation adjustment	(155)	1	(224)	(29)
TOTAL OTHER COMPREHENSIVE INCOME (LOSS)	1,016	14	3,263	2,230
COMPREHENSIVE INCOME	$ 47,125	$ 40,514	$ 141,600	$ 81,700