Investments - Summary of Gross Realized Gains and Losses from Investments before Applicable Income Taxes (Detail) - USD ($) |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2018 |
Sep. 30, 2017 |
Sep. 30, 2018 |
Sep. 30, 2017 |
|
| Gain (Loss) on Securities [Line Items] | ||||
| Gross realized gains | $ 2,981,000 | $ 600,000 | $ 6,262,000 | $ 4,280,000 |
| Gross realized losses | (483,000) | 39,000 | 2,200,000 | 72,000 |
| Net realized gains | 3,463,504 | 561,429 | 4,062,475 | 4,207,710 |
| Fixed Maturities [Member] | ||||
| Gain (Loss) on Securities [Line Items] | ||||
| Gross realized gains | 5,000 | 87,000 | 16,000 | 138,000 |
| Gross realized losses | 25,000 | 39,000 | 70,000 | 69,000 |
| Equity Securities [Member] | ||||
| Gain (Loss) on Securities [Line Items] | ||||
| Gross realized gains | 2,976,000 | $ 513,000 | 6,246,000 | 4,142,000 |
| Gross realized losses | $ (508,000) | $ 2,130,000 | $ 3,000 | |