Deferred Policy Acquisition Costs - Deferred Policy Acquisition Costs (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Deferred Policy Acquisition Costs [Line Items]
Beginning balance	$ 1,497,261
Additions	136,151
Amortization	(129,520)
Effect of change in unrealized gains on available-for-sale debt securities	(38,893)
Net change	(32,262)
Ending balance	1,464,999
Life
Deferred Policy Acquisition Costs [Line Items]
Beginning balance	839,133
Additions	30,763
Amortization	(25,928)
Effect of change in unrealized gains on available-for-sale debt securities	(5,375)
Net change	(540)
Ending balance	838,593
Annuity
Deferred Policy Acquisition Costs [Line Items]
Beginning balance	499,588
Additions	25,077
Amortization	(22,057)
Effect of change in unrealized gains on available-for-sale debt securities	(33,518)
Net change	(30,498)
Ending balance	469,090
Health
Deferred Policy Acquisition Costs [Line Items]
Beginning balance	33,960
Additions	3,087
Amortization	(3,894)
Effect of change in unrealized gains on available-for-sale debt securities	0
Net change	(807)
Ending balance	33,153
Property & Casualty
Deferred Policy Acquisition Costs [Line Items]
Beginning balance	124,580
Additions	77,224
Amortization	(77,641)
Effect of change in unrealized gains on available-for-sale debt securities	0
Net change	(417)
Ending balance	$ 124,163