Schedule II Condensed Financial Information of Registrant - Condensed Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues
Net investment income													$ 365,064	$ 376,507	$ 373,630
Realized investment gains													153,340	(12,543)	(3,406)
Total revenues	$ 331,376	$ 334,418	$ 451,478	$ 313,213	$ 278,535	$ 311,318	$ 306,257	$ 295,489	$ 302,993	$ 289,817	$ 291,436	$ 287,304	1,430,485	1,191,599	1,171,550
Expenses
Interest expense													15,577	13,001	11,948
Total benefits, losses and expenses													1,194,036	1,172,062	1,082,863
Income tax benefit													52,006	1,194	(80,772)
Net income	$ 33,001	$ 25,454	$ 93,822	$ 32,166	$ (20,257)	$ 12,528	$ 5,917	$ 20,155	$ 125,329	$ 26,551	$ 2,261	$ 15,318	184,443	18,343	169,459
Parent company
Revenues
Net investment income													(135)	100	34
Realized investment gains													0	0	0
Total revenues													(135)	100	34
Expenses
Interest expense													14,272	11,892	11,835
Other													12,632	10,898	5,101
Total benefits, losses and expenses													26,904	22,790	16,936
Loss before income tax benefit and equity in net earnings of subsidiaries													(27,039)	(22,690)	(16,902)
Income tax benefit													(6,029)	(4,723)	(6,667)
Loss before equity in net earnings of subsidiaries													(21,010)	(17,967)	(10,235)
Equity in net earnings of subsidiaries													205,453	36,310	179,694
Net income													$ 184,443	$ 18,343	$ 169,459