SCHEDULE IV-REINSURANCE (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
RLI Insurance Group Premiums earned
Direct amount	$ 797,180	$ 781,640	$ 741,569
Ceded to other companies	132,743	167,143	189,658
Assumed from other companies	35,724	72,878	78,891
Net amount	$ 700,161	$ 687,375	$ 630,802
Percentage of amount assumed to net	5.10%	10.60%	12.50%
Casualty segment
RLI Insurance Group Premiums earned
Direct amount	$ 484,435	$ 466,821	$ 425,105
Ceded to other companies	84,311	92,532	103,696
Assumed from other companies	12,124	7,816	2,613
Net amount	$ 412,248	$ 382,105	$ 324,022
Percentage of amount assumed to net	2.90%	2.00%	0.80%
Property segment
RLI Insurance Group Premiums earned
Direct amount	$ 190,678	$ 200,709	$ 203,424
Ceded to other companies	42,731	67,705	79,320
Assumed from other companies	22,977	64,772	76,037
Net amount	$ 170,924	$ 197,776	$ 200,141
Percentage of amount assumed to net	13.40%	32.80%	38.00%
Surety segment
RLI Insurance Group Premiums earned
Direct amount	$ 122,067	$ 114,110	$ 113,040
Ceded to other companies	5,701	6,906	6,642
Assumed from other companies	623	290	241
Net amount	$ 116,989	$ 107,494	$ 106,639
Percentage of amount assumed to net	0.50%	0.30%	0.20%