Fair Value of Financial Instruments - Carrying Amount and Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financial assets
Fair value of bonds held-to-maturity	$ 8,968,690	$ 8,130,084
Fixed maturity securities, bonds available-for-sale	6,725,085	6,215,563
Equity securities	1,700,960	1,530,228
Policy loans	379,657	376,254
Short-term investments	425,321	206,760
Separate account assets	1,073,891	918,369
Financial liabilities
Separate account liabilities	1,073,891	918,369
Carrying Amount
Financial assets
Fair value of bonds held-to-maturity	8,631,261	8,211,449
Fixed maturity securities, bonds available-for-sale	6,725,085	6,215,563
Equity securities	1,700,960	1,530,228
Equity-indexed options	256,005	148,006
Mortgage loans on real estate, net of allowance	5,097,017	5,124,707
Policy loans	379,657	376,254
Short-term investments	425,321	206,760
Separate account assets	1,073,891	918,369
Separately managed accounts	50,503	16,532
Total financial assets	24,339,700	22,747,868
Financial liabilities
Investment contracts	10,254,959	10,003,990
Embedded derivative liability for equity-indexed contracts	731,552	596,075
Notes payable	157,997	137,963
Separate account liabilities	1,073,891	918,369
Total financial liabilities	12,218,399	11,656,397
Fair Value
Financial assets
Fair value of bonds held-to-maturity	8,968,690	8,130,084
Fixed maturity securities, bonds available-for-sale	6,725,085	6,215,563
Equity securities	1,700,960	1,530,228
Equity-indexed options	256,005	148,006
Mortgage loans on real estate, net of allowance	5,309,005	5,049,468
Policy loans	379,657	376,254
Short-term investments	425,321	206,760
Separate account assets	1,073,891	918,369
Separately managed accounts	50,503	16,532
Total financial assets	24,889,117	22,591,264
Financial liabilities
Investment contracts	10,254,959	10,003,990
Embedded derivative liability for equity-indexed contracts	731,552	596,075
Notes payable	157,997	137,963
Separate account liabilities	1,073,891	918,369
Total financial liabilities	12,218,399	11,656,397
Fair Value, Inputs, Level 1, 2 and 3
Financial assets
Separate account assets	1,049,938	905,824
Financial liabilities
Separate account liabilities	$ 1,049,938	$ 905,824

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