Segment Information - Summary of Total Assets by Operating Segments (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total assets	$ 28,597,566	$ 26,912,353	$ 26,386,764
Life
Segment Reporting Information [Line Items]
Total assets	6,825,120	6,263,366	6,101,458
Annuity
Segment Reporting Information [Line Items]
Total assets	13,808,302	12,900,650	12,345,215
Health
Segment Reporting Information [Line Items]
Total assets	511,440	527,525	468,947
Property & Casualty
Segment Reporting Information [Line Items]
Total assets	2,570,818	2,216,628	2,189,515
Corporate & Other
Segment Reporting Information [Line Items]
Total assets	$ 4,881,886	$ 5,004,184	$ 5,281,629