Deferred Policy Acquisition Costs - Deferred Policy Acquisition Costs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Beginning balance	$ 1,373,844	$ 1,294,443	$ 1,324,669
Additions	551,654	525,835	460,213
Amortization	(480,157)	(444,351)	(461,365)
Effect of change in unrealized gains on available-for-sale securities	51,920	(2,083)	(29,074)
Net change	123,417	79,401	(30,226)
Ending balance	1,497,261	1,373,844	1,294,443
Life
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Beginning balance	791,276	745,840	756,023
Additions	131,156	123,854	108,825
Amortization	(97,263)	(74,068)	(112,712)
Effect of change in unrealized gains on available-for-sale securities	13,964	(4,350)	(6,296)
Net change	47,857	45,436	(10,183)
Ending balance	839,133	791,276	745,840
Annuity
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Beginning balance	426,497	394,208	411,206
Additions	92,603	104,772	77,161
Amortization	(57,468)	(74,750)	(71,381)
Effect of change in unrealized gains on available-for-sale securities	37,956	2,267	(22,778)
Net change	73,091	32,289	(16,998)
Ending balance	499,588	426,497	394,208
Health
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Beginning balance	36,806	40,620	44,390
Additions	12,590	11,413	11,203
Amortization	(15,436)	(15,227)	(14,973)
Effect of change in unrealized gains on available-for-sale securities	0	0	0
Net change	(2,846)	(3,814)	(3,770)
Ending balance	33,960	36,806	40,620
Property & Casualty
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Beginning balance	119,265	113,775	113,050
Additions	315,305	285,796	263,024
Amortization	(309,990)	(280,306)	(262,299)
Effect of change in unrealized gains on available-for-sale securities	0	0	0
Net change	5,315	5,490	725
Ending balance	$ 124,580	$ 119,265	$ 113,775