Investments - Summary of Gross Investment Gains and Losses before Applicable Income Taxes (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Gain (Loss) on Securities [Line Items]
Gross investment gains	$ 1,600,000	$ 2,137,000	$ 20,606,000	$ 3,282,000
Gross investment losses	34,000	620,000	943,000	2,683,000
Net investment gains (losses)	1,566,157	1,517,310	19,663,270	598,971
Fixed Maturities [Member]
Gain (Loss) on Securities [Line Items]
Gross investment gains	14,000	12,000	372,000	12,000
Gross investment losses	2,000	1,000	320,000	45,000
Investments In Affiliates [Member]
Gain (Loss) on Securities [Line Items]
Gross investment gains			12,662,000
Equity Securities [Member]
Gain (Loss) on Securities [Line Items]
Gross investment gains	1,586,000	2,125,000	7,572,000	3,270,000
Gross investment losses	$ 32,000	$ 619,000	$ 623,000	$ 2,638,000