Condensed Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement of Comprehensive Income [Abstract]
Net earnings	$ 24,782	$ 24,322	$ 68,405	$ 67,309
Unrealized gains (losses) on securities:
Net unrealized holding gains (losses) arising during period	(1,833)	15,202	(36,065)	28,578
Net unrealized liquidity gains (losses)	(92)	(3)	66	134
Reclassification adjustment for net amounts included in net earnings	(261)	(1,175)	(2,657)	(3,873)
Amortization of net unrealized (gains) losses related to transferred securities	0	(1)	0	0
Net unrealized gains (losses) on securities	(2,186)	14,023	(38,656)	24,839
Foreign currency translation adjustments	(38)	22	555	307
Benefit plans:
Amortization of net prior service cost and net gain (loss)	373	(19)	1,127	429
Other comprehensive income	(1,851)	14,026	(36,974)	25,575
Comprehensive income	$ 22,931	$ 38,348	$ 31,431	$ 92,884