SCHEDULE IV-REINSURANCE (Details) - 10K (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
RLI Insurance Group Premiums earned
Direct amount	$ 781,640	$ 741,569	$ 679,124
Ceded to other companies	167,143	189,658	180,150
Assumed from other companies	72,878	78,891	77,597
Net amount	687,375	630,802	576,571
Percentage of amount assumed to net	10.60%	12.50%	13.50%
Casualty segment
RLI Insurance Group Premiums earned
Direct amount	466,821	425,105	362,724
Ceded to other companies	92,532	103,696	96,039
Assumed from other companies	7,816	2,613	1,012
Net amount	382,105	324,022	267,697
Percentage of amount assumed to net	2.00%	0.80%	0.40%
Property segment
RLI Insurance Group Premiums earned
Direct amount	200,709	203,424	203,072
Ceded to other companies	67,705	79,320	76,817
Assumed from other companies	64,772	76,037	76,147
Net amount	197,776	200,141	202,402
Percentage of amount assumed to net	32.80%	38.00%	37.60%
Surety segment
RLI Insurance Group Premiums earned
Direct amount	114,110	113,040	113,328
Ceded to other companies	6,906	6,642	7,294
Assumed from other companies	290	241	438
Net amount	$ 107,494	$ 106,639	$ 106,472
Percentage of amount assumed to net	0.30%	0.20%	0.40%