Condensed 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 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, 2010		$ 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		4	622
Change in unrealized gains during period, net of tax	6				(1,886)
Cumulative effect of change in accounting principal						0
Amortization						217
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						(16)
Other-than-temporary Impairments, non-credit, net of tax							0
Recoveries, net of tax							0
Change in translation adjustments during period	(75)							(75)
Amortization of net prior service cost and net gain	290								290
Net earnings	18,211									18,211
Stockholder dividends										0
Total stockholders’ equity at Mar. 31, 2011	1,236,158	3,633	37,762	48,938	60,613	(2,512)	0	2,510	(11,673)	1,145,825
Total stockholders’ equity at Dec. 31, 2011	1,276,785	3,635	37,767		69,116	(2,320)	(608)	2,368	(15,380)	1,182,207
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares exercised under stock option plan		0	0
Change in unrealized gains during period, net of tax	7,752				6,713
Cumulative effect of change in accounting principal						0
Amortization						6
Other-than-temporary Impairments, non-credit, net of tax						(51)
Additional Credit Loss On Previously Impaired Securities						0
Change in shadow deferred policy acquistion costs						21	0
Other-than-temporary Impairments, non-credit, net of tax							0
Recoveries, net of tax							0
Change in translation adjustments during period	386							386
Amortization of net prior service cost and net gain	223								223
Net earnings	19,741									19,741
Stockholder dividends										0
Total stockholders’ equity at Mar. 31, 2012	$ 1,303,824	$ 3,635	$ 37,767	$ 60,474	$ 75,829	$ (2,344)	$ (608)	$ 2,754	$ (15,157)	$ 1,201,948