CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
Change in net unrealized gains (losses) on investments, income tax	$ 392,600	$ 400,848	$ 330,213
Reclassification adjustment for investment amounts included in net income, income tax	(3,076)	(14,671)	(5,335)
Change in net unrealized gains (losses) relating to other-than-temporary impaired investments for which a portion has been recognized in earnings, income tax	16,281	(13,205)	11,481
Change in accumulated (loss) gain - derivatives, income tax	2,609	2,382	4,441
Reclassification adjustment for derivative amounts included in net income, income tax	(381)	(138)	(614)
Change in postretirement benefits liability adjustment, income tax	$ (3,498)	$ (10,358)	$ (749)