Investments (Components of Investment Income) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total investment income	$ 461,210	$ 392,073	$ 403,763
Investment expenses	1,162	1,039	2,380
Net investment income	460,048	391,034	401,383
Non-income producing [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Real estate investment	1,500	1,600	3,200
Debt securities [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total investment income	408,204	400,431	363,483
Mortgage loans [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total investment income	11,879	12,123	9,191
Policy loans [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total investment income	5,079	5,143	5,352
Derivative gains (losses) [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total investment income	27,147	(33,335)	16,612
Money market investments [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total investment income	936	273	631
Other investment income [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total investment income	$ 7,965	$ 7,438	$ 8,494