Schedule II - Condensed Financial Information of Registrant (Condensed Statements of Operations) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues:
Net investment income	$ 2,037,475	$ 2,182,078	$ 2,307,635
Change in fair value of derivatives	1,348,735	34,666	906,906
Loss on extinguishment of debt	0	(2,024)	(2,001)
Other revenue	15,670	0	0
Total revenues	3,689,471	2,424,649	3,464,345
Expenses:
Interest expense on notes payable	25,581	25,552	25,525
Interest expense on subordinated debentures issued to subsidiary trusts	5,324	5,557	15,764
Other operating costs and expenses	243,712	183,636	154,153
Total benefits and expenses	3,086,724	1,608,688	3,148,780
Income tax expense	128,755	144,501	69,475
Net income	473,992	671,460	246,090
Less: Preferred stock dividends	43,675	33,515	0
Net income available to common stockholders	430,317	637,945	246,090
Parent Company
Revenues:
Net investment income	114	1,115	1,755
Dividends from subsidiary trusts	159	167	469
Dividends from subsidiaries	250,000	0	0
Surplus note interest from subsidiary	4,080	4,080	4,080
Change in fair value of derivatives	0	62	(1,650)
Loss on extinguishment of debt	0	(2,024)	(2,001)
Other revenue	8,511	346	0
Total revenues	389,507	117,974	110,598
Expenses:
Interest expense on notes payable	25,581	25,552	25,525
Interest expense on subordinated debentures issued to subsidiary trusts	5,324	5,557	15,764
Other operating costs and expenses	72,435	46,686	28,357
Total benefits and expenses	103,340	77,795	69,646
Income before income taxes and equity in undistributed income of subsidiaries	286,167	40,179	40,952
Income tax expense	11,565	13,142	11,586
Income before equity in undistributed income of subsidiaries	274,602	27,037	29,366
Equity in undistributed income of subsidiaries	199,390	644,423	216,724
Net income	473,992	671,460	246,090
Less: Preferred stock dividends	43,675	33,515	0
Net income available to common stockholders	430,317	637,945	246,090
Investment Advisory Fees | Parent Company
Revenues:
Investment advisory fees	$ 126,643	$ 114,228	$ 107,945