Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net earnings	$ 25,483	$ 26,286	$ 49,021	$ 43,545
Unrealized gains (losses) on securities:
Net unrealized holding gains (losses) arising during period	7,788	21,457	13,267	46,103
Net unrealized liquidity gains (losses)	(30)	9	13	18
Reclassification adjustment for net amounts included in net earnings	(1,068)	(113)	(1,758)	(573)
Net unrealized gains (losses) on securities	6,690	21,353	11,522	45,548
Foreign currency translation adjustments	(86)	(203)	(171)	(103)
Benefit plans:
Amortization of net prior service cost and net gain (loss)	(933)	(284)	(1,820)	(567)
Other comprehensive income (loss)	5,671	20,866	9,531	44,878
Comprehensive income (loss)	$ 31,154	$ 47,152	$ 58,552	$ 88,423