Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Consolidated Statements of Comprehensive Income (Loss)
Net income	$ 494,308	$ 496,049	$ 475,543
Unrealized holding gains (losses) on available for sale securities:
Unrealized holding gains (losses) arising during period	112,743	(861,470)	(90,350)
Tax effect	(19,458)	206,281	21,485
Reclassification adjustment for gains included in net income	(43)	(30)	(102)
Tax effect	10	7	24
Net of tax amount	93,252	(655,212)	(68,943)
Change in the retiree medical plan obligation:
Change in the retiree medical plan obligation during period	1,442	(1,110)	98
Tax effect	(356)	272	(23)
Reclassification adjustment for changes included in net income	285	143	174
Tax effect	(71)	(35)	(41)
Net of tax amount	1,300	(730)	208
Other comprehensive income (loss), net of tax	94,552	(655,942)	(68,735)
Comprehensive income (loss)	$ 588,860	$ (159,893)	$ 406,808