Condensed Consolidated Statements of Comprehensive Income (Loss) - 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	$ 10,825	$ 19,989	$ 57,176	$ 93,883
Unrealized gains (losses) on securities:
Net unrealized holding gains (losses) arising during period	24,357	15,586	53,569	93,730
Net unrealized liquidity gains (losses)	1	1	2	3
Reclassification adjustment for net amounts included in net earnings	(702)	1,380	(2,670)	4,252
Net unrealized gains (losses) on securities	23,656	16,967	50,901	97,985
Foreign currency translation adjustments	85	52	(46)	519
Benefit plans:
Amortization of net prior service cost and net gain (loss)	(2,066)	(504)	(6,199)	(1,512)
Other comprehensive income (loss)	21,675	16,515	44,656	96,992
Comprehensive income (loss)	$ 32,500	$ 36,504	$ 101,832	$ 190,875