Investments (Components of Investment Income) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total investment income	$ 506,516,000	$ 661,459,000	$ 461,210,000
Investment expenses	1,086,000	1,027,000	1,162,000
Net investment income	505,430,000	660,432,000	460,048,000
Non-income producing [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Real estate investment	900,000	1,300,000	1,500,000
Debt securities [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total investment income	410,809,000	410,790,000	408,204,000
Mortgage loans [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total investment income	9,847,000	9,256,000	11,879,000
Policy loans [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total investment income	4,252,000	4,503,000	5,079,000
Derivative gains (losses) [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total investment income	68,616,000	225,899,000	27,147,000
Money market investments [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total investment income	401,000	252,000	936,000
Other investment income [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total investment income	$ 12,591,000	$ 10,759,000	$ 7,965,000