Condensed Consolidated Statements of Stockholders' Equity (USD $) In Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Net Unrealized Investment Gain (Loss) [Member]	Accumulated Other-than-Temporary Impairment Held-To-Maturity [Member]	Accumulated Other Than Temporary Impairment Available For Sale [Member]	Accumulated Translation Adjustment [Member]	Accumulated Defined Benefit Plans Adjustment [Member]	Retained Earnings [Member]
Total stockholders’ equity at Dec. 31, 2009		$ 3,626	$ 36,680		$ 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	274
Change in unrealized gains during period, net of tax	49,093				48,435
Cumulative effect of change in accounting principal						0
Amortization						30
Other-than-temporary Impairments, non-credit, net of tax						(123)
Additional Credit Loss On Previously Impaired Securities						0
Change in shadow deferred policy acquistion costs						0	0
Other-than-temporary Impairments, non-credit, net of tax							0
Recoveries, net of tax							326
Change in translation adjustments during period	(139)							(139)
Amortization of net prior service cost and net gain	868								868
Net earnings	52,659									52,659
Stockholder dividends										(1,271)
Total stockholders’ equity at Sep. 30, 2010	1,215,115	3,629	36,954	67,157	80,074	(2,844)	(236)	2,754	(12,591)	1,107,375
Total stockholders’ equity at Dec. 31, 2010	1,218,791	3,629	37,140		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	901
Change in unrealized gains during period, net of tax	11,318				7,188
Cumulative effect of change in accounting principal						0
Amortization						163
Other-than-temporary Impairments, non-credit, net of tax						0
Additional Credit Loss On Previously Impaired Securities						0
Change in shadow deferred policy acquistion costs						184	(622)
Other-than-temporary Impairments, non-credit, net of tax							(1,117)
Recoveries, net of tax							0
Change in translation adjustments during period	(155)							(155)
Amortization of net prior service cost and net gain	819								819
Net earnings	51,265									51,265
Stockholder dividends										(1,271)
Total stockholders’ equity at Sep. 30, 2011	$ 1,277,396	$ 3,635	$ 38,041	$ 58,112	$ 69,687	$ (2,366)	$ (495)	$ 2,430	$ (11,144)	$ 1,177,608