Schedule II - Condensed Financial Information of Registrant (Condensed Statements of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues:
Net investment income	$ 475,633	$ 463,583	$ 459,830	$ 450,826	$ 438,262	$ 436,085	$ 418,176	$ 399,669	$ 1,849,872	$ 1,692,192	$ 1,531,667
Change in fair value of derivatives	95,391	103,794	39,099	(74,065)	69,338	(351,360)	(23,024)	(31,100)	164,219	(336,146)	504,825
Loss on extinguishment of debt									0	0	(12,502)
Total revenues	622,816	630,060	549,802	417,604	541,883	126,965	441,094	408,995	2,220,282	1,518,937	2,168,973
Expenses:
Change in fair value of embedded derivatives									543,465	(464,698)	32,321
Interest expense on notes and loan payable									28,248	28,849	36,370
Interest expense on subordinated debentures issued to subsidiary trusts									12,958	12,239	12,122
Other operating costs and expenses									102,231	96,218	81,584
Total benefits and expenses									2,090,035	1,181,623	1,972,909
Income tax expense									47,004	117,484	70,041
Net income	$ 120,796	$ (7,420)	$ 14,708	$ (44,841)	$ 33,776	$ 97,306	$ 82,845	$ 5,903	83,243	219,830	126,023
Parent Company [Member]
Revenues:
Net investment income									78	62	130
Dividends from subsidiary trusts									384	363	360
Investment advisory fees									75,706	65,957	58,044
Surplus note interest from subsidiary									4,080	4,080	4,080
Change in fair value of derivatives									(810)	(8,225)	(17,122)
Loss on extinguishment of debt									0	0	(12,502)
Total revenues									79,438	62,237	32,990
Expenses:
Change in fair value of embedded derivatives									0	(4,516)	(15,227)
Interest expense on notes and loan payable									28,248	28,849	36,370
Interest expense on subordinated debentures issued to subsidiary trusts									12,958	12,239	12,122
Other operating costs and expenses									8,551	8,195	7,928
Total benefits and expenses									49,757	44,767	41,193
Income (loss) before income taxes and equity in undistributed income of subsidiaries									29,681	17,470	(8,203)
Income tax expense									12,073	7,338	664
Income (loss) before equity in undistributed income of subsidiaries									17,608	10,132	(8,867)
Equity in undistributed income of subsidiaries									65,635	209,698	134,890
Net income									$ 83,243	$ 219,830	$ 126,023