Condensed Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Statement of Comprehensive Income [Abstract]
Net earnings	$ 29,183	$ 26,991	$ 49,009	$ 43,623
Unrealized gains (losses) on securities:
Net unrealized holding gains (losses) arising during period	10,892	(33,107)	21,894	(34,232)
Net unrealized liquidity gains (losses)	28	20	51	158
Reclassification adjustment for net amounts included in net earnings	(1,946)	(1,037)	(2,371)	(2,396)
Amortization of net unrealized (gains) losses related to transferred securities	0	0	0	0
Net unrealized gains (losses) on securities	8,974	(34,124)	19,574	(36,470)
Foreign currency translation adjustments	(122)	3	(633)	593
Benefit plans:
Amortization of net prior service cost and net gain (loss)	(175)	373	(351)	754
Other comprehensive income (loss)	8,677	(33,748)	18,590	(35,123)
Comprehensive income (loss)	$ 37,860	$ (6,757)	$ 67,599	$ 8,500