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]	Unrealized gains on non-impaired securities [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, 2011		$ 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	13,376				10,679
Amortization						15
Other-than-temporary impairments, non-credit, net of tax						92
Additional credit loss on previously impaired securities						0
Change in shadow deferred policy acquistion costs						30	0
Other-than-temporary impairments, non-credit, net of tax							0
Recoveries, net of tax							0
Change in translation adjustments during period	285							285
Amortization of net prior service cost and net gain, net of tax	448								448
Net earnings	42,987									42,987
Stockholder dividends										0
Total stockholders’ equity at Jun. 30, 2012	1,331,321	3,635	37,767	64,725	79,795	(2,183)	(608)	2,653	(14,932)	1,225,194
Total stockholders’ equity at Dec. 31, 2012	1,391,680	3,635	37,767		91,972	(1,426)	(196)	2,589	(16,153)	1,273,492
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares exercised under stock option plan		0	0
Change in unrealized gains during period, net of tax	(34,232)				(36,628)
Amortization						77
Other-than-temporary impairments, non-credit, net of tax						23
Additional credit loss on previously impaired securities						14
Change in shadow deferred policy acquistion costs						(77)	(123)
Other-than-temporary impairments, non-credit, net of tax							0
Recoveries, net of tax							244
Change in translation adjustments during period	593							593
Amortization of net prior service cost and net gain, net of tax	754								754
Net earnings	43,623									43,623
Stockholder dividends										0
Total stockholders’ equity at Jun. 30, 2013	$ 1,400,180	$ 3,635	$ 37,767	$ 41,663	$ 55,344	$ (1,389)	$ (75)	$ 3,182	$ (15,399)	$ 1,317,115