Condensed Financial Information of Parent Company - Summary of Condensed Statements of (Loss) Income and Comprehensive (Loss) Income (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Total revenues	$ 186,805,834	$ 199,904,180	$ 195,790,028	$ 189,328,278	$ 190,758,831	$ 185,716,027	$ 183,580,716	$ 178,970,963	$ 771,828,320	$ 739,026,537	$ 688,423,020
Expenses
Interest									2,302,082	1,593,437	1,657,647
Total expenses	143,395,401	140,726,106	135,753,645	156,583,268	130,442,303	114,386,379	128,005,914	114,433,458	820,065,169	726,912,075	647,094,613
Income (loss) before income tax expense (benefit) and equity in undistributed net (loss) income of subsidiaries									(48,236,849)	12,114,462	41,328,407
Income tax expense (benefit)									(15,476,509)	4,998,362	10,527,270
Net (loss) income	(14,998,763)	1,206,356	(789,855)	(18,178,078)	(2,778,644)	7,108,574	(2,318,648)	5,104,818	(32,760,340)	7,116,100	30,801,137
Statements of Comprehensive (Loss) Income
Net (loss) income	$ (14,998,763)	$ 1,206,356	$ (789,855)	$ (18,178,078)	$ (2,778,644)	$ 7,108,574	$ (2,318,648)	$ 5,104,818	(32,760,340)	7,116,100	30,801,137
Other comprehensive (loss) income, net of tax
Unrealized (loss) gain-subsidiaries									(7,019,532)	3,811,151	(1,386,391)
Comprehensive (loss) income									(39,385,469)	7,161,783	27,773,122
Parent Company [Member]
Revenues
Dividends from subsidiaries									11,000,000	13,000,000	13,000,000
Other									3,196,000	2,131,000	1,759,000
Total revenues									14,196,000	15,131,000	14,759,000
Expenses
Operating expenses									1,628,000	1,433,000	1,413,000
Interest									2,224,000	1,929,000	1,747,000
Total expenses									3,852,000	3,362,000	3,160,000
Income (loss) before income tax expense (benefit) and equity in undistributed net (loss) income of subsidiaries									10,344,000	11,769,000	11,599,000
Income tax expense (benefit)									411,000	(690,000)	(931,000)
Income before equity in undistributed net (loss) income of subsidiaries									9,933,000	12,459,000	12,530,000
Equity in undistributed net (loss) income of subsidiaries									(42,694,000)	(5,343,000)	18,271,000
Net (loss) income									(32,760,000)	7,116,000	30,801,000
Statements of Comprehensive (Loss) Income
Net (loss) income									(32,760,000)	7,116,000	30,801,000
Other comprehensive (loss) income, net of tax
Unrealized (loss) gain-subsidiaries									(6,625,000)	46,000	(3,028,000)
Other comprehensive (loss) income, net of tax									(6,625,000)	46,000	(3,028,000)
Comprehensive (loss) income									$ (39,385,000)	$ 7,162,000	$ 27,773,000