Consolidated Statements of Stockholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated other comprehensive income (loss) [Member]	Unrealized losses on impaired held to maturity securities [Member]	Unrealized losses on impaired available for sale securities [Member]	Foreign currency translation adjustments [Member]	Benefit plan liability adjustment [Member]	Retained Earnings [Member]
Total stockholders’ equity at Dec. 31, 2008		$ 3,626	$ 36,680		$ (53,770)	$ 0	$ 0	$ 2,966	$ (14,554)	$ 1,011,265
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares exercised under stock option plan		0	0
Change in unrealized gains (losses) during period	82,686				85,409
Cumulative effect of change in accounting principal (see Note 1)						(507)				507
Amortization						43
Other-than-temporary Impairments						(2,287)
Other-than-temporary Impairments							(581)
Recoveries							19
Change in translation adjustments during period	(73)							(73)
Amortization of net prior service cost and net gain	1,095								1,095
Net earnings	45,484									45,484
Stockholder dividends										(1,269)
Total stockholders’ equity at Dec. 31, 2009	1,114,053	3,626	36,680	17,760	31,639	(2,751)	(562)	2,893	(13,459)	1,055,987
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares exercised under stock option plan		3	460
Change in unrealized gains (losses) during period	33,417				30,860
Cumulative effect of change in accounting principal (see Note 1)						0				0
Amortization						38
Other-than-temporary Impairments						0
Other-than-temporary Impairments							0
Recoveries							562
Change in translation adjustments during period	(308)							(308)
Amortization of net prior service cost and net gain	1,496								1,496
Net earnings	72,897									72,897
Stockholder dividends										(1,270)
Total stockholders’ equity at Dec. 31, 2010	1,218,791	3,629	37,140	50,408	62,499	(2,713)	0	2,585	(11,963)	1,127,614
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares exercised under stock option plan		6	627
Change in unrealized gains (losses) during period	10,955				6,617
Cumulative effect of change in accounting principal (see Note 1)						0				0
Amortization						33
Other-than-temporary Impairments						360
Other-than-temporary Impairments							(608)
Recoveries							0
Change in translation adjustments during period	(217)							(217)
Amortization of net prior service cost and net gain	(3,417)								(3,417)
Net earnings	55,627									55,627
Stockholder dividends										(1,273)
Total stockholders’ equity at Dec. 31, 2011	$ 1,276,785	$ 3,635	$ 37,767	$ 53,176	$ 69,116	$ (2,320)	$ (608)	$ 2,368	$ (15,380)	$ 1,182,207