Segment Information - Summary of Financial Data by Segment (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Premiums earned
Net premiums earned	$ 177,283,816	$ 166,809,851	$ 521,454,835	$ 487,227,767
Net investment income	5,979,834	5,581,238	17,385,103	16,471,630
Realized investment gains	561,429	1,018,415	4,207,710	2,204,533
Equity in earnings of DFSC	403,647	357,956	1,023,212	698,658
Other	1,487,000	1,544,000	4,197,000	4,623,000
Total revenues	185,716,027	175,311,263	548,267,706	511,226,906
Underwriting income (loss):
SAP underwriting income (loss)	79,000	(2,160,000)	(19,146,000)	7,165,000
GAAP adjustments	644,000	788,000	6,423,000	5,795,000
GAAP underwriting income (loss)	723,000	(1,372,000)	(12,723,000)	12,960,000
Net investment income	5,979,834	5,581,238	17,385,103	16,471,630
Realized investment gains	561,429	1,018,415	4,207,710	2,204,533
Equity in earnings of DFSC	403,647	357,956	1,023,212	698,658
Other	844,000	844,000	1,947,000	2,157,000
Income before income tax expense	8,512,050	6,429,039	11,840,410	34,493,270
Commercial Lines [Member]
Premiums earned
Net premiums earned	80,724,000	75,571,000	236,437,000	218,405,000
Underwriting income (loss):
SAP underwriting income (loss)	8,998,000	3,701,000	12,670,000	14,118,000
Personal Lines [Member]
Premiums earned
Net premiums earned	96,560,000	91,239,000	285,018,000	268,823,000
Underwriting income (loss):
SAP underwriting income (loss)	$ (8,919,000)	$ (5,861,000)	$ (31,816,000)	$ (6,953,000)