Consolidated Statement of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Income and Comprehensive Income [Abstract]
Net earnings	$ 458,343us-gaap_NetIncomeLoss	$ 407,197us-gaap_NetIncomeLoss	$ 391,240us-gaap_NetIncomeLoss
Investment gains (losses):
Investment gains (losses) during the period	175,219	(240,601)	135,746
Income tax charge (benefit)	62,055	(85,377)	46,779
Investments gains (losses), net of tax	113,164	(155,224)	88,967
Less reclassification adjustments to:
Net realized investment gain	(66,370)	(42,030)	(31,148)
Other-than-temporary impairment credit losses			(1,028)
Income tax expense	(23,230)	(14,711)	(10,542)
Total reclassifications included in net earnings, net of tax	(43,140)	(27,319)	(19,578)
Net unrealized investment gains (losses)	70,024	(182,543)	69,389
Foreign currency translation adjustment	(9,529)	6,078	(2,720)
Income tax charge (benefit)	4,132	155	(943)
Foreign currency translation adjustment, net of tax	(13,661)	5,923	(1,777)
Other comprehensive income (loss)	56,363	(176,620)	67,612
Comprehensive income	$ 514,706us-gaap_ComprehensiveIncomeNetOfTax	$ 230,577us-gaap_ComprehensiveIncomeNetOfTax	$ 458,852us-gaap_ComprehensiveIncomeNetOfTax

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