Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2010
Cash flows from operating activities:
Net income	$ 238,114	$ 202,237	[1]	$ 195,534	[1]
Adjustments to reconcile net income to net cash provided by operating activities:
Earnings allocated to participating policyholders	(580)	2,884		2,197
Amortization of premiums (accretion of discounts) on investments, net	(28,495)	(41,220)		(44,096)
Net realized (gains) losses on investments	(126,938)	(62,088)		26,665
Net proceeds (purchases) of trading securities	(220,646)	3,597		901
Interest credited to contractholders	515,356	525,347		514,002
Depreciation and amortization	82,595	48,094		44,540
Deferral of acquisition costs	(94,826)	(57,108)		(47,513)
Deferred income taxes	45,371	23,617		33,636
Other, net	(2,681)	(4,037)		(9,834)
Changes in assets and liabilities:
Policy benefit liabilities	(192,755)	(148,298)		135,731
Reinsurance receivable	(15,893)	1,131		4,594
Investment income due and accrued	(8,654)	(8,769)		(13,896)
Other assets	(98,042)	(8,176)		9,256
Other liabilities	31,380	45,515		(112,002)
Net cash provided by operating activities	123,306	522,726		739,715
Proceeds from sales, maturities and redemptions of investments:
Fixed maturities, available-for-sale	8,432,248	5,373,914		4,515,507
Mortgage loans on real estate	172,950	96,848		158,246
Limited partnership interests, other corporation interests and other investments	52,151	58,872		90,235
Purchases of investments:
Fixed maturities, available-for-sale	(9,407,969)	(6,405,522)		(5,355,943)
Mortgage loans on real estate	(524,396)	(899,234)		(331,843)
Limited partnership interests, other corporation interests and other investments	(5,577)	(7,874)		(19,528)
Net change in short-term investments	81,058	1,576,779		(919,023)
Net change in repurchase agreements		(936,762)		445,424
Policy loans, net	4,983	(41,408)		24,257
Purchases of furniture, equipment and software	(23,525)	(19,990)
Net cash used in investing activities	(1,218,077)	(1,204,377)		(1,392,668)
Cash flows from financing activities:
Contract deposits	2,881,112	2,544,213		2,234,984
Contract withdrawals	(1,636,066)	(1,716,544)		(1,570,767)
Change in due to/from parent and affiliates	37,598	87,743		(16,274)
Dividends paid	(184,401)	(206,353)		(160,917)
Net commercial paper borrowings	451	5,855		(5,932)
Change in book overdrafts	(609)	(31,963)		3,898
Income tax benefit of stock option exercises	480	1,817		1,459
Net cash provided by financing activities	1,098,565	684,768		486,451
Net increase (decrease) in cash	3,794	3,117		(166,502)
Cash, beginning of year	7,593	4,476		170,978
Cash, end of year	11,387	7,593		4,476
Net cash paid (received) during the year for:
Income taxes	(102,213)	(121,436)		33
Income tax payments withheld and remitted to taxing authorities	48,932	53,630		56,664
Interest	37,387	37,463		37,421
Non-cash investing and financing transactions during the years:
Share-based compensation expense	2,314	1,786		1,855
Fair value of assets acquired in settlement of fixed maturity investments	1,125	13,021
Real estate acquired in satisfaction of debt		$ 2,140

[1] As adjusted; See Note 1