Consolidated Statements of Comprehensive Income (Loss) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net earnings	$ 105,588	$ 96,247	$ 92,558
Unrealized gains (losses) on securities:
Net unrealized holding gains (losses) arising during period	12,536	(42,218)	27,211
Net unrealized liquidity gains (losses)	26	333	1,307
Reclassification adjustment for net amounts included in net earnings	(5,000)	(3,061)	(4,504)
Amortization of net unrealized (gains) losses related to transferred securities	0	0	148
Net unrealized gains (losses) on securities	7,562	(44,946)	24,162
Foreign currency translation adjustments	(556)	652	221
Benefit plans:
Amortization of net prior service cost and net gain, net of tax	(3,300)	5,588	(773)
Other comprehensive income (loss)	3,706	(38,706)	23,610
Comprehensive income (loss)	$ 109,294	$ 57,541	$ 116,168