Consolidated Statements of Stockholders' Equity (USD $)	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, 2009		$ 3,626,000	$ 36,680,000		$ 31,639,000	$ (2,751,000)	$ (562,000)	$ 2,893,000	$ (13,459,000)	$ 1,055,987,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares exercised under stock option plan		3,000	460,000
Change in unrealized gains (losses) during period	33,417,000				30,717,000
Cumulative Effect on Retained Earnings, Net of Tax (Correction to Compensation Costs Associated With Stock Options [Member])
Amortization						38,000
Other-than-temporary Impairments						589,000
Additional Credit Loss On Previously Impaired Securities						0
Other-than-temporary Impairments							1,033,000
Change in shadow deferred policy acquisition costs						(387,000)	(530,000)
Recoveries							0
Change in translation adjustments during period	(308,000)							(308,000)
Amortization of net prior service cost and net gain	1,496,000								1,496,000
Net earnings	72,897,000									72,897,000
Stockholder dividends										(1,270,000)
Total stockholders’ equity at Dec. 31, 2010	1,218,791,000	3,629,000	37,140,000	50,408,000	62,356,000	(2,511,000)	(59,000)	2,585,000	(11,963,000)	1,127,614,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares exercised under stock option plan		6,000	627,000
Change in unrealized gains (losses) during period	10,955,000				6,761,000
Cumulative Effect on Retained Earnings, Net of Tax (Correction to Compensation Costs Associated With Stock Options [Member])	239,000
Amortization						33,000
Other-than-temporary Impairments						(38,000)
Additional Credit Loss On Previously Impaired Securities						106,000
Other-than-temporary Impairments							(1,118,000)
Change in shadow deferred policy acquisition costs						89,000	569,000
Recoveries
Change in translation adjustments during period	(217,000)							(217,000)
Amortization of net prior service cost and net gain	(3,417,000)								(3,417,000)
Net earnings	55,627,000									55,627,000
Stockholder dividends										(1,273,000)
Total stockholders’ equity at Dec. 31, 2011	1,276,785,000	3,635,000	37,767,000	53,176,000	69,117,000	(2,321,000)	(608,000)	2,368,000	(15,380,000)	1,182,207,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares exercised under stock option plan		0	0
Change in unrealized gains (losses) during period	27,211,000				22,855,000
Cumulative Effect on Retained Earnings, Net of Tax (Correction to Compensation Costs Associated With Stock Options [Member])	0
Amortization						393,000
Other-than-temporary Impairments						289,000
Additional Credit Loss On Previously Impaired Securities						411,000
Other-than-temporary Impairments							0
Change in shadow deferred policy acquisition costs						(198,000)	(424,000)
Recoveries							836,000
Change in translation adjustments during period	221,000							221,000
Amortization of net prior service cost and net gain	(773,000)								(773,000)
Net earnings	92,558,000									92,558,000
Stockholder dividends										(1,273,000)
Total stockholders’ equity at Dec. 31, 2012	$ 1,391,680,000	$ 3,635,000	$ 37,767,000	$ 76,786,000	$ 91,972,000	$ (1,426,000)	$ (196,000)	$ 2,589,000	$ (16,153,000)	$ 1,273,492,000