Unaudited Selected Quarterly Financial Information (Schedule of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unaudited Selected Quarterly Financial Information [Abstract]
Total revenue	$ 97,375	$ 97,723	$ 93,475	$ 96,948	$ 97,254	$ 97,618	$ 91,052	$ 90,028	$ 385,521	$ 375,952	$ 372,402
Total expense	113,342	99,248	98,393	91,110	103,428	90,442	89,565	84,039	402,093	367,474	340,516
Income (loss) before tax	(15,967)	(1,525)	(4,918)	5,838	(6,174)	7,176	1,487	5,989	(16,572)	8,478	31,886
Income tax expense (benefit)	(5,338)	35	(1,568)	1,852	(2,512)	2,128	421	1,915	(5,019)	1,952	10,023
Net income (loss)	$ (10,629)	$ (1,560)	$ (3,350)	$ 3,986	$ (3,662)	$ 5,048	$ 1,066	$ 4,074	(11,553)	6,526	21,863
Net income (loss) attributable to Hallmark Financial Services, Inc.									$ (11,553)	$ 6,526	$ 21,863
Basic earnings (loss) per share:	$ (0.59)	$ (0.09)	$ (0.18)	$ 0.21	$ (0.20)	$ 0.27	$ 0.06	$ 0.21	$ (0.63)	$ 0.35	$ 1.14
Diluted earnings (loss) per share:	$ (0.59)	$ (0.09)	$ (0.18)	$ 0.21	$ (0.20)	$ 0.27	$ 0.06	$ 0.21	$ (0.63)	$ 0.34	$ 1.13