Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income	$ 231,092	$ 190,455	$ 317,369
Adjustments to reconcile net income to net cash provided by operating activities:
Losses allocated to participating policyholders	(1,024)	(1,267)	(1,041)
Amortization of premiums (accretion of discounts) on investments, net	2,209	(12,213)	(42,022)
Net realized (gains) losses on investments	(75,472)	(73,331)	(64,323)
Net proceeds (purchases) of trading securities	107,770	(277,510)	11,478
Interest credited to contractholders	606,790	577,548	571,860
Depreciation and amortization	74,987	139,735	76,461
Deferral of acquisition costs	(93,621)	(64,709)	(110,843)
Deferred income taxes	53,481	21,682	75,044
Contingent consideration	(209)	(17,600)	0
Amortization of low-income housing partnerships	372	4,563	21,713
Other, net	(1,366)	(3,072)	(4,984)
Changes in assets and liabilities:
Policy benefit liabilities	(231,952)	(273,507)	(151,096)
Reinsurance recoverable	10,340	8,738	(18,054)
Investment income due and accrued	(4,392)	(4,385)	(8,951)
Other, net	(23,705)	8,949	(12,273)
Net cash provided by operating activities	655,300	224,076	660,338
Proceeds from sales, maturities, and redemptions of investments:
Fixed maturities, available-for-sale	6,229,209	5,470,124	4,124,159
Mortgage loans on real estate	389,663	594,497	384,306
Limited partnership interests, other corporation interests, and other investments	10,742	6,833	7,555
Purchases of investments:
Fixed maturities, available-for-sale	(7,840,166)	(6,468,699)	(5,174,996)
Mortgage loans on real estate	(694,127)	(448,924)	(609,008)
Limited partnership interests, other corporation interests, and other investments	(5,766)	(1,527)	(2,983)
Net change in short-term investments	(39,677)	(2,238)	22,096
Policy loans, net	5,527	98,143	(11,169)
Acquisition payment	0	0	(28,356)
Purchases of furniture, equipment, and software	(44,644)	(78,778)	(35,537)
Net cash used in investing activities	(1,989,239)	(830,569)	(1,323,933)
Cash flows from financing activities:
Contract deposits	3,546,320	2,527,039	2,709,043
Contract withdrawals	(2,098,286)	(1,782,571)	(1,757,936)
Change in due to/from parent and affiliates	(21,719)	(22,359)	49,337
Dividends paid	(125,691)	(139,533)	(316,401)
Proceeds from issuance of common stock	19,750	60,803	0
Proceeds from financing element derivatives	0	0	5,516
Payments for and interest paid on financing element derivatives, net	(6,744)	(9,383)	(8,392)
Payment of contingent consideration	(14,400)	0	0
Net commercial paper borrowings	5,678	(5,218)	(401)
Change in book overdrafts	12,713	(1,651)	(12,052)
Income tax benefit of stock option exercises	277	953	165
Net cash provided by financing activities	1,317,898	628,080	668,879
Net (decrease) increase in cash	(16,041)	21,587	5,284
Cash, beginning of year	34,362	12,775	7,491
Cash, end of year	18,321	34,362	12,775
Net cash (paid) received during the year for:
Income taxes	(1,543)	(4,093)	46,453
Interest	(31,254)	(37,288)	(37,284)
Non-cash investing and financing transactions during the years:
Share-based compensation expense	(2,190)	(1,655)	(3,384)
Contingent consideration	$ 0	$ 0	$ (32,209)