Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Net earnings	$ 28,858	$ 29,183	$ 50,184	$ 49,009
Unrealized gains (losses) on securities:
Net unrealized holding gains (losses) arising during period	(21,202)	10,892	(11,830)	21,894
Net unrealized liquidity gains (losses)	32	28	93	51
Reclassification adjustment for net amounts included in net earnings	(1,855)	(1,946)	(2,020)	(2,371)
Net unrealized gains (losses) on securities	(23,025)	8,974	(13,757)	19,574
Foreign currency translation adjustments	(53)	(122)	(12)	(633)
Benefit plans:
Amortization of net prior service cost and net gain (loss)	(304)	(175)	(607)	(351)
Other comprehensive income (loss)	(23,382)	8,677	(14,376)	18,590
Comprehensive income (loss)	$ 5,476	$ 37,860	$ 35,808	$ 67,599