Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net earnings	$ 92,312	$ 131,616	$ 116,758
Unrealized gains (losses) on securities:
Net unrealized holding gains (losses) arising during period	352,561	96,954	(56,818)
Net unrealized liquidity gains (losses)	6	3	2
Reclassification adjustment for net amounts included in net earnings	(4,485)	3,997	(2,718)
Net unrealized gains (losses) on securities	348,082	100,954	(59,534)
Foreign currency translation adjustments	15	524	1,354
Benefit plans:
Amortization of net prior service cost and net gain (loss)	(12,784)	(4,355)	11,298
Other comprehensive income (loss)	335,313	97,123	(46,882)
Comprehensive income (loss)	$ 427,625	$ 228,739	$ 69,876