Variable Interest Entity (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Investments [Abstract]
Debt maturities, held to maturity, at amortized cost	$ 6,387	$ 7,417
Equity securities, available for sale, at fair value	38,086	39,247
Total investments	386,388	330,763
Cash and short term investments	76,161	40,157	$ 45,926	$ 41,446
Premiums receivable, net	34,928	27,275
Deferred policy acquisition costs	13,522	13,610
Other assets	10,973	7,231
Total assets	634,307	503,631
LIABILITIES AND SHAREHOLDERS' EQUITY [Abstract]
Unpaid losses and LAE	91,673	78,330		$ 61,016
Unearned premiums	250,397	192,424
Accounts payable and accrued expenses	16,403	10,924
Debt	5,000	0
Total liabilities	392,825	311,052
Shareholders' equity [Abstract]
Common stock, $0.01 par value. Issued and outstanding 100 shares	138	136
Additional paid-in capital	131,203	127,302
Accumulated other comprehensive income [Abstract]
Unrealized net gains on investments, available for sale	4,838	7,718
Total accumulated other comprehensive income	4,838	7,718
Retained earnings	87,188	57,423
Total shareholders' equity	241,482	192,579
Total liabilities and shareholders' equity	$ 634,307	$ 503,631
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares issued (in shares)	13,773,130	13,632,414
Common stock, shares outstanding (in shares)	13,773,130	13,632,414
Variable Interest Entity (VIE) [Member]
Investments [Abstract]
Debt maturities, held to maturity, at amortized cost	$ 21,877	$ 0
Equity securities, available for sale, at fair value	1,350	0
Total investments	23,227	0
Cash and short term investments	13,492	0
Premiums receivable, net	326	0
Deferred policy acquisition costs	168	0
Deferred income taxes, net	665	0
Other assets	178	0
Total assets	38,056	0
LIABILITIES AND SHAREHOLDERS' EQUITY [Abstract]
Unpaid losses and LAE	112	0
Unearned premiums	1,072	0
Income taxes payable	110	0
Accounts payable and accrued expenses	249	0
Debt	5,000	0
Total liabilities	6,543	0
Shareholders' equity [Abstract]
Common stock, $0.01 par value. Issued and outstanding 100 shares	0	0
Additional paid-in capital	32,413	0
Accumulated other comprehensive income [Abstract]
Unrealized net gains on investments, available for sale	(234)	0
Total accumulated other comprehensive income	(234)	0
Retained earnings	(666)	0
Total shareholders' equity	31,513	0
Total liabilities and shareholders' equity	$ 38,056	$ 0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares issued (in shares)	100	100
Common stock, shares outstanding (in shares)	100	100