CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 60,012	$ 41,477	$ 158,215	$ 107,498
Other comprehensive (loss) income, net of tax
Unrealized gain (loss) on debt securities arising during the period	(16,943)	5,434	(35,693)	27,861
Change in retirement obligation	438	401	1,259	1,082
Other comprehensive income (loss)	(16,505)	5,835	(34,434)	28,943
Comprehensive income	$ 43,507	$ 47,312	$ 123,781	$ 136,441