Condensed Consolidated Statements of Comprehensive Earnings - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net earnings	$ 39,997	$ 28,860	$ 96,182	$ 79,927
Other comprehensive earnings
Unrealized gain (loss) on marketable securities, net of tax	(1,659)	1,337	2,283	10,419
Other comprehensive earnings (loss)	(1,659)	1,337	2,283	10,419
Comprehensive earnings	$ 38,338	$ 30,197	$ 98,465	$ 90,346