Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Comprehensive Income [Abstract]
Net earnings	$ 48,413	$ 33,696	$ 46,351	$ 73,894
Unrealized gains (losses) on securities:
Net unrealized holding gains (losses) arising during period	107,365	35,401	29,212	78,144
Net unrealized liquidity gains (losses)	0	1	1	2
Reclassification adjustment for net amounts included in net earnings	(1,367)	3,740	(1,968)	2,872
Net unrealized gains (losses) on securities	105,998	39,142	27,245	81,018
Foreign currency translation adjustments	(92)	(86)	(131)	467
Benefit plans:
Amortization of net prior service cost and net gain (loss)	(2,067)	(504)	(4,133)	(1,008)
Other comprehensive income (loss)	103,839	38,552	22,981	80,477
Comprehensive income (loss)	$ 152,252	$ 72,248	$ 69,332	$ 154,371