Investments (Net Unrealized Gain (Loss) on Investments) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Investments, Debt and Equity Securities [Abstract]
Gross unrealized gains	$ 270,967	$ 212,588
Gross unrealized losses	(9,133)	(18,603)
Deferred policy acquisition costs and sales inducements	(122,799)	(92,160)
Deferred federal income tax expense	(48,685)	(35,675)
Adjustments for deferred expense, deferred policy acquisition and sales inducement cost	90,350	66,150
Net unrealized gains related to securities transferred to held to maturity	0	38
Net unrealized gains on investment securities	$ 90,350	$ 66,188