Schedule II - Condensed Financial Information of Registrant - Condensed Statements of Financial Position (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
ASSETS
Equity securities	$ 1,530,228	$ 1,784,226
Mortgage loans on real estate, net of allowance	5,124,707	4,749,999
Other invested assets	50,087	80,165
Deferred policy acquisition costs	1,497,261	1,373,844	$ 1,294,443	$ 1,324,669
Separate account assets	918,369	969,764
Prepaid pension	57,117	0
Other assets	163,222	158,024
Total assets	26,912,353	26,386,764	$ 24,533,222
LIABILITIES
Policyholders’ account balances	12,461,833	12,060,045
Separate account liabilities	918,369	969,764
Other liabilities	452,985	477,855
Total liabilities	21,640,838	21,130,993
EQUITY
Common stock	30,832	30,832
Additional paid-in capital	20,694	19,193
Accumulated other comprehensive income (loss)	(99,738)	642,216
Retained earnings	5,413,952	4,656,134
Treasury stock, at cost	(108,492)	(101,616)
Total equity	5,257,248	5,246,759
Total liabilities and equity	26,912,353	26,386,764
Parent Company
ASSETS
Fixed maturity securities	9,660,562	9,093,442
Equity securities	6,252	4,976
Mortgage loans on real estate, net of allowance	4,772,085	4,533,620
Other invested assets	1,487,383	1,961,343
Investment in subsidiaries	3,121,901	3,090,883
Deferred policy acquisition costs	1,224,752	1,116,862
Separate account assets	918,369	969,764
Prepaid pension	57,117	0
Other assets	763,458	873,470
Total assets	22,011,879	21,644,360
LIABILITIES
Policy liabilities	4,373,398	4,207,467
Policyholders’ account balances	10,943,189	10,690,282
Separate account liabilities	918,369	969,764
Other liabilities	519,675	530,088
Total liabilities	16,754,631	16,397,601
EQUITY
Common stock	30,832	30,832
Additional paid-in capital	20,694	19,193
Accumulated other comprehensive income (loss)	(99,738)	642,216
Retained earnings	5,413,952	4,656,134
Treasury stock, at cost	(108,492)	(101,616)
Total equity	5,257,248	5,246,759
Total liabilities and equity	$ 22,011,879	$ 21,644,360