Investments (Details 9) (USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Major Categories Of Investment Income Net Of Expenses [Line Items]
Investment Revenue	$ 1,475,396,000	$ 1,311,289,000	$ 1,263,663,000
Investment Income, Investment Expense	(39,190,000)	(30,092,000)	(25,003,000)
Investment income, net of related expenses	1,436,206,000	1,281,197,000	1,238,660,000
Available-for-sale Securities [Member]
Major Categories Of Investment Income Net Of Expenses [Line Items]
Investment Revenue	868,682,000	757,726,000	715,817,000
Mortgage Loans on Real Estate [Member]
Major Categories Of Investment Income Net Of Expenses [Line Items]
Investment Revenue	96,901,000	55,931,000	51,186,000
Policy Loans [Member]
Major Categories Of Investment Income Net Of Expenses [Line Items]
Investment Revenue	62,855,000	66,621,000	72,743,000
Funds Withheld At Interest [Member]
Major Categories Of Investment Income Net Of Expenses [Line Items]
Investment Revenue	393,586,000	388,694,000	385,762,000
Short-term Investments [Member]
Major Categories Of Investment Income Net Of Expenses [Line Items]
Investment Revenue	4,173,000	2,378,000	4,968,000
Other Aggregated Investments [Member]
Major Categories Of Investment Income Net Of Expenses [Line Items]
Investment Revenue	$ 49,199,000	$ 39,939,000	$ 33,187,000