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, 2012		$ 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	(1,125)				(2,483)
Amortization						0
Other-than-temporary impairments, non-credit, net of tax						0
Additional credit loss on previously impaired securities						25
Other-than-temporary impairments, non-credit, net of tax							0
Change in shadow deferred policy acquisition costs						(17)	(133)
Recoveries, net of tax							263
Change in translation adjustments during period	590							590
Amortization of net prior service cost and net gain, net of tax	381								381
Net earnings	16,632									16,632
Stockholder dividends										0
Total stockholders’ equity at Mar. 31, 2013	1,406,938	3,635	37,767	75,412	89,489	(1,418)	(66)	3,179	(15,772)	1,290,124
Total stockholders’ equity at Dec. 31, 2013	1,447,948				46,693	(1,287)	(2)	3,241	(10,565)	1,368,466
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares exercised under stock option plan		0	0
Change in unrealized gains during period, net of tax	11,002				10,578
Amortization						57
Other-than-temporary impairments, non-credit, net of tax						0
Additional credit loss on previously impaired securities						0
Other-than-temporary impairments, non-credit, net of tax							0
Change in shadow deferred policy acquisition costs						(35)	(1)
Recoveries, net of tax							2
Change in translation adjustments during period	(511)							(511)
Amortization of net prior service cost and net gain, net of tax	(176)								(176)
Net earnings	19,826									19,826
Stockholder dividends										0
Total stockholders’ equity at Mar. 31, 2014	$ 1,477,688	$ 3,635	$ 37,767	$ 47,994	$ 57,271	$ (1,265)	$ (1)	$ 2,730	$ (10,741)	$ 1,388,292