Investments - Summary of Gross Realized Gains and Losses from Investments before Applicable Income Taxes (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Gain (Loss) on Investments [Line Items]
Gross realized gains	$ 2,549,000	$ 1,165,000
Gross realized losses		694,000
Net realized gains (losses)	2,548,975	470,941
Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Gross realized gains	5,000	1,165,000
Gross realized losses		255,000
Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Gross realized gains	$ 2,544,000
Gross realized losses		$ 439,000