Consolidated Statements of Income and Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues:
Gross written premiums	$ 223,191	$ 188,478	$ 177,009
Ceded written premiums	(33,719)	(21,214)	(92,991)
Net written premiums	189,472	167,264	84,018
Change in unearned premiums	(13,419)	(33,448)	(9,696)
Net earned premiums	176,053	133,816	74,322
Net investment income	10,569	7,487	5,643
Net investment gains (losses):
Net realized investment gains, excluding other-than-temporary impairment losses	151	452	59
Other-than-temporary impairment losses	0	(276)	0
Net investment gains	151	176	59
Other income	3	136	572
Total revenues	186,776	141,615	80,596
Expenses:
Losses and loss adjustment expenses	103,680	70,961	42,238
Underwriting, acquisition and insurance expenses	44,146	28,551	2,809
Other expenses	429	2,567	1,992
Total expenses	148,255	102,079	47,039
Income before income taxes	38,521	39,536	33,557
Income tax expense (benefit)	13,620	13,369	11,284
Net income	24,901	26,167	22,273
Other comprehensive income (loss):
Unrealized gains (losses), net of taxes of $3,047 in 2017, $(344) in 2016, and $(841) in 2015	6,384	(640)	(1,563)
Total comprehensive income	$ 31,285	$ 25,527	$ 20,710
Common Stock [Member]
Earnings per share:
Earnings per share - basic (in dollars per share)	$ 1.19	$ 0.57	$ 0.00
Earnings per share - diluted (in dollars per share)	$ 1.16	$ 0.56	$ 0.00
Weighted-average common shares outstanding:
Basic weighted average shares outstanding (in shares)	20,992	20,841	0
Diluted weighed average shares outstanding (in shares)	21,498	21,073	0
Class A Common Stock [Member]
Earnings per share:
Earnings per share - basic (in dollars per share)	$ 0.00	$ 0.98	$ 1.53
Earnings per share - diluted (in dollars per share)	$ 0.00	$ 0.98	$ 1.53
Weighted-average common shares outstanding:
Basic weighted average shares outstanding (in shares)	0	13,844	13,796
Diluted weighed average shares outstanding (in shares)	0	13,844	13,796
Class B Common Stock [Member]
Earnings per share:
Earnings per share - basic (in dollars per share)	$ 0.00	$ 0.48	$ 0.84
Earnings per share - diluted (in dollars per share)	$ 0.00	$ 0.46	$ 0.81
Weighted-average common shares outstanding:
Basic weighted average shares outstanding (in shares)	0	1,574	1,413
Diluted weighed average shares outstanding (in shares)	0	1,644	1,452